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  • Receiving DB update events in .NET from SQLite

    - by Dan Tao
    I've recently discovered the awesomeness of SQLite, specifically the .NET wrapper for SQLite at http://sqlite.phxsoftware.com/. Now, suppose I'm developing software that will be running on multiple machines on the same network. Nothing crazy, probably only 5 or 6 machines. And each of these instances of the software will be accessing an SQLite database stored in a file in a shared directory (is this a bad idea? If so, tell me!). Is there a way for each instance of the app to be notifiied if one instance updates the database file? One obvious way would be to use the FileSystemWatcher class, read the entire database into a DataSet, and then ... you know ... enumerate through the entire thing to see what's new ... but yeah, that seems pretty idiotic, actually. Is there such a thing as a provider of SQLite updates? Does this even make sense as a question? I'm also pretty much a newbie when it comes to ADO.NET, so I might be approaching the problem from the entirely wrong angle.

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  • Why would the VB.NET compiler think an interface isn't implemented when it is?

    - by Dan Tao
    I have this happen sometimes, particularly with the INotifyPropertyChanged interface in my experience but I have no idea if the problem is limited to that single interface (which would seem bizarre) or not. Let's say I have some code set up like this. There's an interface with a single event. A class implements that interface. It includes the event. Public Interface INotifyPropertyChanged Event PropertyChanged As PropertyChangedEventHandler End Interface Public Class Person Implements INotifyPropertyChanged Public Event PropertyChanged _ (ByVal sender As Object, ByVal e As PropertyChangedEventArgs) _ Implements INotifyPropertyChanged.PropertyChanged ' more code below ' End Class Every now and then, when I build my project, the compiler will suddenly start acting like the above code is broken. It will report that the Person class does not implement INotifyPropertyChanged because it doesn't have a PropertyChanged event; or it will say the PropertyChanged event can't implement INotifyPropertyChanged.PropertyChanged because their signatures don't match. This is weird enough as it is, but here's the weirdest part: if I just cut out the line starting with Event PropertyChanged and then paste it back in, the error goes away. The project builds. Does anybody have any clue what could be going on here?

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  • Custom View embed in Gallery crashes while key press

    - by tao
    Hi there, I'd like to find some stuff to replace the Tab component, so I'd make a custom View named StringView, which has the ability to display text, and to embed it into a Gallery. But it always crashes with error "NullPointerException at InputMethodManager". I have no idea about this, any help&tip&suggest are appreciate. Detail of my issue: First I'd created a class StringView extends View: public class StringView extends View { protected final Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG); protected String mString; protected int mAscent; // Constructor public StringView(Context context, String string) { super(context); mPaint.setARGB(255, 255, 60, 10); mPaint.setTextSize(30); //mPaint.setFakeBoldText(true); mString = string; setPadding(20,15,20,15); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); int w = this.getPaddingLeft(); int h = this.getPaddingTop() - mAscent; canvas.drawText(mString, w, h, mPaint); } public void setString(String str) { mString = str; this.requestLayout(); this.invalidate(); } public String getString() { return mString; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { setMeasuredDimension(measureWidth(widthMeasureSpec), measureHeight(heightMeasureSpec)); } /** * Determines the width of this view * @param measureSpec A measureSpec packed into an int * @return The width of the view, honoring constraints from measureSpec */ private int measureWidth(int measureSpec) { int result = 0; int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec); if (specMode == MeasureSpec.EXACTLY) { // We were told how big to be result = specSize; } else { // Measure the text result = (int) mPaint.measureText(mString) + getPaddingLeft() + getPaddingRight(); if (specMode == MeasureSpec.AT_MOST) { // Respect AT_MOST value if that was what is called for by measureSpec result = Math.min(result, specSize); } } return result; } /** * Determines the height of this view * @param measureSpec A measureSpec packed into an int * @return The height of the view, honoring constraints from measureSpec */ private int measureHeight(int measureSpec) { int result = 0; int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec); mAscent = (int) mPaint.ascent(); if (specMode == MeasureSpec.EXACTLY) { // We were told how big to be result = specSize; } else { // Measure the text (beware: ascent is a negative number) result = (int) (-mAscent + mPaint.descent()) + getPaddingTop() + getPaddingBottom(); if (specMode == MeasureSpec.AT_MOST) { // Respect AT_MOST value if that was what is called for by measureSpec result = Math.min(result, specSize); } } return result; } } Second I put it in to Gallery through Adapter Gallery gallery = (Gallery) findViewById(R.id.gallery); gallery.setAdapter(new ImageAdapter(this)); ImageAdapter: public class ImageAdapter extends BaseAdapter { int mGalleryItemBackground; private Context mContext; private View[] mImages = genSerielImageViews(); public ImageAdapter(Context c) { mContext = c; TypedArray a = obtainStyledAttributes(R.styleable.Gallery); mGalleryItemBackground = a.getResourceId( R.styleable.Gallery_android_galleryItemBackground, 0); a.recycle(); } private View[] genSerielImageViews() { if (true) { int N = 6; StringView[] views = new StringView[N]; for (int i=0; i<N; i++) { views[i] = new StringView(mContext, "ITEM #" + Integer.toString(i) ); } return views; } else { int N = 6; TextView[] views = new TextView[N]; for (int i=0; i<N; i++) { views[i] = new TextView( mContext ); views[i].setText("CCTV #" + Integer.toString(i) ); } return views; } } public int getCount() { return mImages.length; } public Object getItem(int position) { return position; } public long getItemId(int position) { return position; } public View getView(int position, View convertView, ViewGroup parent) { return mImages[position]; } } Then Compile&Run, press keypad RIGHT and I got a crash, It's turns out a weird InputMethodManager error: 03-18 07:22:33.568: ERROR/AndroidRuntime(958): Uncaught handler: thread main exiting due to uncaught exception 03-18 07:22:33.648: ERROR/AndroidRuntime(958): java.lang.NullPointerException 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.view.inputmethod.InputMethodManager.startInputInner(InputMethodManager.java:940) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.view.inputmethod.InputMethodManager.checkFocus(InputMethodManager.java:1114) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.view.ViewRoot.handleMessage(ViewRoot.java:1869) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.os.Handler.dispatchMessage(Handler.java:99) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.os.Looper.loop(Looper.java:123) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at android.app.ActivityThread.main(ActivityThread.java:4310) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at java.lang.reflect.Method.invokeNative(Native Method) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at java.lang.reflect.Method.invoke(Method.java:521) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 03-18 07:22:33.648: ERROR/AndroidRuntime(958): at dalvik.system.NativeStart.main(Native Method) Thanks.

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  • How is IObservable<double>.Average supposed to work?

    - by Dan Tao
    Update Looks like Jon Skeet was right (big surprise!) and the issue was with my assumption about the Average extension providing a continuous average (it doesn't). For the behavior I'm after, I wrote a simple ContinuousAverage extension method, the implementation of which I am including here for the benefit of others who may want something similar: public static class ObservableExtensions { private class ContinuousAverager { private double _mean; private long _count; public ContinuousAverager() { _mean = 0.0; _count = 0L; } // undecided whether this method needs to be made thread-safe or not // seems that ought to be the responsibility of the IObservable (?) public double Add(double value) { double delta = value - _mean; _mean += (delta / (double)(++_count)); return _mean; } } public static IObservable<double> ContinousAverage(this IObservable<double> source) { var averager = new ContinuousAverager(); return source.Select(x => averager.Add(x)); } } I'm thinking of going ahead and doing something like the above for the other obvious candidates as well -- so, ContinuousCount, ContinuousSum, ContinuousMin, ContinuousMax ... perhaps ContinuousVariance and ContinuousStandardDeviation as well? Any thoughts on that? Original Question I use Rx Extensions a little bit here and there, and feel I've got the basic ideas down. Now here's something odd: I was under the impression that if I wrote this: var ticks = Observable.FromEvent<QuoteEventArgs>(MarketDataProvider, "MarketTick"); var bids = ticks .Where(e => e.EventArgs.Quote.HasBid) .Select(e => e.EventArgs.Quote.Bid); var bidsSubscription = bids.Subscribe( b => Console.WriteLine("Bid: {0}", b) ); var avgOfBids = bids.Average(); var avgOfBidsSubscription = avgOfBids.Subscribe( b => Console.WriteLine("Avg Bid: {0}", b) ); I would get two IObservable<double> objects (bids and avgOfBids); one would basically be a stream of all the market bids from my MarketDataProvider, the other would be a stream of the average of these bids. So something like this: Bid Avg Bid 1 1 2 1.5 1 1.33 2 1.5 It seems that my avgOfBids object isn't doing anything. What am I missing? I think I've probably misunderstood what Average is actually supposed to do. (This also seems to be the case for all of the aggregate-like extension methods on IObservable<T> -- e.g., Max, Count, etc.)

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  • If I'm updating a DataRow, do I lock the entire DataTable or just the DataRow?

    - by Dan Tao
    Suppose I'm accessing a DataTable from multiple threads. If I want to access a particular row, I suspect I need to lock that operation (I could be mistaken about this, but at least I know this way I'm safe): // this is a strongly-typed table OrdersRow row = null; lock (orderTable.Rows.SyncRoot) { row = orderTable.FindByOrderId(myOrderId); } But then, if I want to update that row, should I lock the table (or rather, the table's Rows.SyncRoot object) again, or can I simply lock the row?

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  • What statistics can be maintained for a set of numerical data without iterating?

    - by Dan Tao
    Update Just for future reference, I'm going to list all of the statistics that I'm aware of that can be maintained in a rolling collection, recalculated as an O(1) operation on every addition/removal (this is really how I should've worded the question from the beginning): Obvious Count Sum Mean Max* Min* Median** Less Obvious Variance Standard Deviation Skewness Kurtosis Mode*** Weighted Average Weighted Moving Average**** OK, so to put it more accurately: these are not "all" of the statistics I'm aware of. They're just the ones that I can remember off the top of my head right now. *Can be recalculated in O(1) for additions only, or for additions and removals if the collection is sorted (but in this case, insertion is not O(1)). Removals potentially incur an O(n) recalculation for non-sorted collections. **Recalculated in O(1) for a sorted, indexed collection only. ***Requires a fairly complex data structure to recalculate in O(1). ****This can certainly be achieved in O(1) for additions and removals when the weights are assigned in a linearly descending fashion. In other scenarios, I'm not sure. Original Question Say I maintain a collection of numerical data -- let's say, just a bunch of numbers. For this data, there are loads of calculated values that might be of interest; one example would be the sum. To get the sum of all this data, I could... Option 1: Iterate through the collection, adding all the values: double sum = 0.0; for (int i = 0; i < values.Count; i++) sum += values[i]; Option 2: Maintain the sum, eliminating the need to ever iterate over the collection just to find the sum: void Add(double value) { values.Add(value); sum += value; } void Remove(double value) { values.Remove(value); sum -= value; } EDIT: To put this question in more relatable terms, let's compare the two options above to a (sort of) real-world situation: Suppose I start listing numbers out loud and ask you to keep them in your head. I start by saying, "11, 16, 13, 12." If you've just been remembering the numbers themselves and nothing more, and then I say, "What's the sum?", you'd have to think to yourself, "OK, what's 11 + 16 + 13 + 12?" before responding, "52." If, on the other hand, you had been keeping track of the sum yourself while I was listing the numbers (i.e., when I said, "11" you thought "11", when I said "16", you thought, "27," and so on), you could answer "52" right away. Then if I say, "OK, now forget the number 16," if you've been keeping track of the sum inside your head you can simply take 16 away from 52 and know that the new sum is 36, rather than taking 16 off the list and them summing up 11 + 13 + 12. So my question is, what other calculations, other than the obvious ones like sum and average, are like this? SECOND EDIT: As an arbitrary example of a statistic that (I'm almost certain) does require iteration -- and therefore cannot be maintained as simply as a sum or average -- consider if I asked you, "how many numbers in this collection are divisible by the min?" Let's say the numbers are 5, 15, 19, 20, 21, 25, and 30. The min of this set is 5, which divides into 5, 15, 20, 25, and 30 (but not 19 or 21), so the answer is 5. Now if I remove 5 from the collection and ask the same question, the answer is now 2, since only 15 and 30 are divisible by the new min of 15; but, as far as I can tell, you cannot know this without going through the collection again. So I think this gets to the heart of my question: if we can divide kinds of statistics into these categories, those that are maintainable (my own term, maybe there's a more official one somewhere) versus those that require iteration to compute any time a collection is changed, what are all the maintainable ones? What I am asking about is not strictly the same as an online algorithm (though I sincerely thank those of you who introduced me to that concept). An online algorithm can begin its work without having even seen all of the input data; the maintainable statistics I am seeking will certainly have seen all the data, they just don't need to reiterate through it over and over again whenever it changes.

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  • How can I add an Items-like property to my User Control?

    - by Dan Tao
    It's pretty straightforward to add simple properties to a User Control that will appear in the desired categories in the Windows Forms designer, e.g.: [Category("Appearance")] public Color BackColor { get { return _textBox.BackColor; } set { _textBox.BackColor = value; } } What if I want to expose a more complex property, such as a collection of items of a type I define? I'm thinking something along the lines of the ListView.Items property, or the DataGridView.Columns property -- where the user of the control can access this complex property via a more specialized pop-up form (as opposed to a simple TextBox or ComboBox). Even a simple nudge in the right direction would be much appreciated.

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  • Event on Item Marked as Read in Outlook - Delphi COM Add-in

    - by Tao
    I have a Delphi COM Add-in for Outlook (2000-2007) and am trying to find a way to register an event when an MailItem in Outlook is marked as read. I want to add an additional property to the item as/just after it is marked as read. Does anyone have any idea how to do this using the Outlook Object Model? I am also using Add-In-Express components to help get to additional properties events.

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  • Why might a System.String object not cache its hash code?

    - by Dan Tao
    A glance at the source code for string.GetHashCode using Reflector reveals the following (for mscorlib.dll version 4.0): public override unsafe int GetHashCode() { fixed (char* str = ((char*) this)) { char* chPtr = str; int num = 0x15051505; int num2 = num; int* numPtr = (int*) chPtr; for (int i = this.Length; i > 0; i -= 4) { num = (((num << 5) + num) + (num >> 0x1b)) ^ numPtr[0]; if (i <= 2) { break; } num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr[1]; numPtr += 2; } return (num + (num2 * 0x5d588b65)); } } Now, I realize that the implementation of GetHashCode is not specified and is implementation-dependent, so the question "is GetHashCode implemented in the form of X or Y?" is not really answerable. I'm just curious about a few things: If Reflector has disassembled the DLL correctly and this is the implementation of GetHashCode (in my environment), am I correct in interpreting this code to indicate that a string object, based on this particular implementation, would not cache its hash code? Assuming the answer is yes, why would this be? It seems to me that the memory cost would be minimal (one more 32-bit integer, a drop in the pond compared to the size of the string itself) whereas the savings would be significant, especially in cases where, e.g., strings are used as keys in a hashtable-based collection like a Dictionary<string, [...]>. And since the string class is immutable, it isn't like the value returned by GetHashCode will ever even change. What could I be missing? UPDATE: In response to Andras Zoltan's closing remark: There's also the point made in Tim's answer(+1 there). If he's right, and I think he is, then there's no guarantee that a string is actually immutable after construction, therefore to cache the result would be wrong. Whoa, whoa there! This is an interesting point to make (and yes it's very true), but I really doubt that this was taken into consideration in the implementation of GetHashCode. The statement "therefore to cache the result would be wrong" implies to me that the framework's attitude regarding strings is "Well, they're supposed to be immutable, but really if developers want to get sneaky they're mutable so we'll treat them as such." This is definitely not how the framework views strings. It fully relies on their immutability in so many ways (interning of string literals, assignment of all zero-length strings to string.Empty, etc.) that, basically, if you mutate a string, you're writing code whose behavior is entirely undefined and unpredictable. I guess my point is that for the author(s) of this implementation to worry, "What if this string instance is modified between calls, even though the class as it is publicly exposed is immutable?" would be like for someone planning a casual outdoor BBQ to think to him-/herself, "What if someone brings an atomic bomb to the party?" Look, if someone brings an atom bomb, party's over.

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  • Helpful advice on developing a professional MS Word add-on

    - by Dan Tao
    A few months back I put together a simple proof-of-concept piece of software for a small firm with an idea for a document editing tool. The company wanted this tool to be integrated into Microsoft Word, understandably, to maximize its accessibility to the average user. I essentially wrote the underlying library with all of the core functionality as a C# project, and then used VSTO to get it running inside of Word. It felt like a bit of a duct tape solution, really; but then, I have (practically) zero experience developing tools for integration with MS Office, and it was only a proof of concept anyway. Well, the firm was quite pleased with my work overall, and they're looking to move from "proof of concept" to the real deal. Fortunately, as I said, the core functionality is all there and will only need to be somewhat tweaked and enhanced. My main concern is figuring out how to put together an application that will integrate with MS Word in a clean and polished way, and which can be deployed easily in accordance with a regular user's expectations (i.e., simply running an install program and voila, it's there in Word). I seem to remember reading somewhere that nobody uses VSTO for real professional projects. Is this true? False? What are the alternatives? And what are the tips and gotchas that I should be aware of before getting started on this issue of MS Word integration?

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  • Group variables in a boxplot in R

    - by tao.hong
    I am trying to generate a boxplot whose data come from two scenarios. In the plot, I would like to group boxes by their names (So there will be two boxes per variable). I know ggplot would be a good choice. But I got errors which I could not figure out. Can anyone give me some suggestions? sensitivity_out1 structure(c(0.0522902104339716, 0.0521369824334004, 0.0520240345973737, 0.0519818337359876, 0.051935071418996, 0.0519089404325544, 0.000392698277338341, 0.000326135474295325, 0.000280863338343747, 0.000259631566041935, 0.000246594043996332, 0.000237923540393391, 0.00046732650331544, 0.000474448907808135, 0.000478287273678457, 0.000480194683464109, 0.000480631753078668, 0.000481760272726273, 0.000947965771207979, 0.000944821699830455, 0.000939631071343889, 0.000937186900570605, 0.000936007346568281, 0.000934756220144141, 0.00132442589501872, 0.00132658367774979, 0.00133334696220742, 0.00133622384928092, 0.0013381577476241, 0.00134005741746304, 0.0991622968751298, 0.100791399440082, 0.101946808417405, 0.102524244727408, 0.102920085260477, 0.103232984259916, 0.0305219507186844, 0.0304635269233494, 0.0304161055015213, 0.0303742106794513, 0.0303381888169022, 0.0302996157711171, 1.94268588634518e-05, 2.23991225564447e-05, 2.5756135487907e-05, 2.79997917298194e-05, 3.00753967077715e-05, 3.16270817369878e-05, 0.544701146678523, 0.542887331601984, 0.541632986366816, 0.541005610554556, 0.540617004208336, 0.540315690692195, 0.000453386694666078, 0.000448473414508756, 0.00044692043197248, 0.000444826296854332, 0.000445747996014684, 0.000444764303682453, 0.000127569551159321, 0.000128422491392669, 0.00012933662856487, 0.000129941842982939, 0.000129578971489026, 0.000131113075233758, 0.00684610571790029, 0.00686349387897349, 0.00687468164010565, 0.00687880720347743, 0.00688275579317197, 0.00687822247621936), .Dim = c(6L, 12L)) out2 structure(c(0.0189965816735366, 0.0189995096225103, 0.0190099362589894, 0.0190033523148514, 0.01900896721937, 0.0190099427513381, 0.00192043989797585, 0.00207303208721059, 0.00225931163225165, 0.0024049969048389, 0.00252310364086785, 0.00262940166568126, 0.00195164921633517, 0.00190079923515755, 0.00186139563778548, 0.00184188171395076, 0.00183248544676564, 0.00182492970673969, 1.83038731485927e-05, 1.98252671720347e-05, 2.14794764479231e-05, 2.30713122969332e-05, 2.4484220713564e-05, 2.55958833705284e-05, 0.0428066864455102, 0.0431686808647809, 0.0434411033615353, 0.0435883377765726, 0.0436690169266633, 0.0437340464360965, 0.145288252474567, 0.141488776430307, 0.138204532539654, 0.136281799717717, 0.134864952272761, 0.133738386148036, 0.0711728636959696, 0.072031388688795, 0.0727536853228245, 0.0731581966147734, 0.0734424337399303, 0.0736637270702609, 0.000605277151497094, 0.000617268349064968, 0.000632975679951382, 0.000643904422677427, 0.000653775268094148, 0.000662225067910141, 0.26735354610469, 0.267515415990146, 0.26753155165617, 0.267553498616325, 0.267532284594615, 0.267510330320289, 0.000334158771646756, 0.000319032383145857, 0.000306074699839994, 0.000299153278494114, 0.000293956197852583, 0.000290171804454218, 0.000645975219899115, 0.000637548672578787, 0.000632375486965757, 0.000629579821884212, 0.000624956458229123, 0.000622456283217054, 0.0645188290106884, 0.0651539609630352, 0.0656417364889907, 0.0658996698322889, 0.0660715073023965, 0.0662034341510152), .Dim = c(6L, 12L)) Melt data: group variable value 1 1 PLDKRT 0 2 1 PLDKRT 0 3 1 PLDKRT 0 4 1 PLDKRT 0 5 1 PLDKRT 0 6 1 PLDKRT 0 Code: #Data_source 1 sensitivity_1=rbind(sensitivity_out1,sensitivity_out2) sensitivity_1=data.frame(sensitivity_1) colnames(sensitivity_1)=main_l #variable names sensitivity_1$group=1 #Data_source 2 sensitivity_2=rbind(sensitivity_out1[3:4,],sensitivity_out2[3:4,]) sensitivity_2=data.frame(sensitivity_2) colnames(sensitivity_2)=main_l sensitivity_2$group=2 sensitivity_pool=rbind(sensitivity_1,sensitivity_2) sensitivity_pool_m=melt(sensitivity_pool,id.vars="group") ggplot(data = sensitivity_pool_m, aes(x = variable, y = value)) + geom_boxplot(aes( fill= group), width = 0.8) Error: "Error in unit(tic_pos.c, "mm") : 'x' and 'units' must have length > 0" Update Figure out the error. I should use geom_boxplot(aes( fill= factor(group)), width = 0.8) rather than fill= group

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  • Enable debugging in Design mode in VS

    - by Dan Tao
    Is there any way to enable debugging from within the Windows Forms Designer in Visual Studio (any version, up to and including 2010)? What I mean is, say I have some custom user control, and this control has certain validation that it performs when I set a particular property. I'd like to be able to set a breakpoint somewhere within that code, and step through it to see what happens when I set the property from the designer.

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  • UIWebView in multithread ViewController

    - by Tao
    I have a UIWebView in a viewcontroller, which has two methods as below. The question is if I pop out(tap back on navigation bar) this controller before the second thread is done, the app will crash after [super dealloc], because "Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread.". Any help would be really appreciated. -(void)viewDidAppear:(BOOL)animated { [super viewWillAppear:animated]; NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(load) object:nil]; [operationQueue addOperation:operation]; [operation release]; } -(void)load { [NSThread sleepForTimeInterval:5]; [self performSelectorOnMainThread:@selector(done) withObject:nil waitUntilDone:NO]; }

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  • For loop with a non-integer increment in VB.NET

    - by Dan Tao
    Can a VB.NET For loop be constructed that mimics this C# code? TimeSpan oneDay = TimeSpan.FromDays(1.0); for (DateTime d = startDate; d < endDate; d += oneDay) { // some code } Obviously you could do it without a For loop (i.e., with a While); I'm just curious if there's a certain syntax to construct a VB.NET For loop with a non-integer increment that I'm not aware of.

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  • How to analyse contents of binary serialization stream?

    - by Tao
    I'm using binary serialization (BinaryFormatter) as a temporary mechanism to store state information in a file for a relatively complex (game) object structure; the files are coming out much larger than I expect, and my data structure includes recursive references - so I'm wondering whether the BinaryFormatter is actually storing multiple copies of the same objects, or whether my basic "number of objects and values I should have" arithmentic is way off-base, or where else the excessive size is coming from. Searching on stack overflow I was able to find the specification for Microsoft's binary remoting format: http://msdn.microsoft.com/en-us/library/cc236844(PROT.10).aspx What I can't find is any existing viewer that enables you to "peek" into the contents of a binaryformatter output file - get object counts and total bytes for different object types in the file, etc; I feel like this must be my "google-fu" failing me (what little I have) - can anyone help? This must have been done before, right??

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  • How would you implement this "WorkerChain" functionality in .NET?

    - by Dan Tao
    Sorry for the vague question title -- not sure how to encapsulate what I'm asking below succinctly. (If someone with editing privileges can think of a more descriptive title, feel free to change it.) The behavior I need is this. I am envisioning a worker class that accepts a single delegate task in its constructor (for simplicity, I would make it immutable -- no more tasks can be added after instantiation). I'll call this task T. The class should have a simple method, something like GetToWork, that will exhibit this behavior: If the worker is not currently running T, then it will start doing so right now. If the worker is currently running T, then once it is finished, it will start T again immediately. GetToWork can be called any number of times while the worker is running T; the simple rule is that, during any execution of T, if GetToWork was called at least once, T will run again upon completion (and then if GetToWork is called while T is running that time, it will repeat itself again, etc.). Now, this is pretty straightforward with a boolean switch. But this class needs to be thread-safe, by which I mean, steps 1 and 2 above need to comprise atomic operations (at least I think they do). There is an added layer of complexity. I have need of a "worker chain" class that will consist of many of these workers linked together. As soon as the first worker completes, it essentially calls GetToWork on the worker after it; meanwhile, if its own GetToWork has been called, it restarts itself as well. Logically calling GetToWork on the chain is essentially the same as calling GetToWork on the first worker in the chain (I would fully intend that the chain's workers not be publicly accessible). One way to imagine how this hypothetical "worker chain" would behave is by comparing it to a team in a relay race. Suppose there are four runners, W1 through W4, and let the chain be called C. If I call C.StartWork(), what should happen is this: If W1 is at his starting point (i.e., doing nothing), he will start running towards W2. If W1 is already running towards W2 (i.e., executing his task), then once he reaches W2, he will signal to W2 to get started, immediately return to his starting point and, since StartWork has been called, start running towards W2 again. When W1 reaches W2's starting point, he'll immediately return to his own starting point. If W2 is just sitting around, he'll start running immediately towards W3. If W2 is already off running towards W3, then W2 will simply go again once he's reached W3 and returned to his starting point. The above is probably a little convoluted and written out poorly. But hopefully you get the basic idea. Obviously, these workers will be running on their own threads. Also, I guess it's possible this functionality already exists somewhere? If that's the case, definitely let me know!

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  • Is there a non-blocking version of MessageBox.Show (or something like it)?

    - by Dan Tao
    Often you just want to notify the user that something has occurred, but there's really no need for any input from them. In this common scenario, I sometimes see code like this: MessageBox.Show("Something has occurred", "Something", MessageBoxButtons.OK); This code, as we all know, causes a little pop-up window to appear with only an OK button. Now here's the thing: this code blocks (the UI thread). But in the vast majority of cases, it seems to me, if you only have an OK button, there's very little need to block. (Isn't the purpose of blocking typically to receive some input from the user? And if the user's only choice is "OK," in this typical case, isn't blocking pretty pointless?) Obviously I could just write my own little form that does basically exactly what MessageBox.Show does, except that it returns nothing (no DialogResult) and doesn't block. But I was just wondering if something like this exists already that I didn't know about.

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  • How can I get an IObservable<T> in Rx from a "non-standard" event?

    - by Dan Tao
    Here's what I mean. Suppose I'm working with an API that exposes events, but these events do not follow the standard EventHandler or EventHandler<TEventArgs> signature. One event might look like this, for instance: Public Event Update(ByVal sender As BaseSubscription, ByVal e As BaseEvent) Now, typically, if I want to get an IObservable<TEventArgs> from an event, I can just do this: Dim updates = Observable.FromEvent(Of UpdateEventArgs)( _ target:=updateSource, _ eventName:="Update" _ ) But this doesn't work, because the Update event is not an EventHandler<UpdateEventArgs> -- in fact, there is no UpdateEventArgs -- it's basically just its own thing. Obviously, I could define my own class deriving from EventArgs (i.e., UpdateEventArgs), write another class to wrap the object providing the Update event, give the wrapper class its own Update event that is an EventHandler<UpdateEventArgs>, and get an IObservable<UpdateEventArgs> from that. But that's an annoying amount of work. Is there some way to create an IObservable<[something]> from a "non-standard" event like this, or am I out of luck?

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  • Can I configure a strongly typed data set to use nullable values?

    - by Dan Tao
    If I have a strongly typed data table with a column for values of type Int32, and this column allows nulls, then I'll get an exception if I do this for a row where the value is null: int value = row.CustomValue; Instead I need to do this: if (!row.IsCustomValueNull()) { int value = row.CustomValue; // do something with this value } Ideally I would like to be able to do this: int? value = row.CustomValue; Of course I could always write my own method, something like GetCustomValueOrNull; but it'd be preferable if the property auto-generated for the column itself simply returned a nullable. Is this possible?

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  • What are the fastest-performing options for a read-only, unordered collection of unique strings?

    - by Dan Tao
    Disclaimer: I realize the totally obvious answer to this question is HashSet<string>. It is absurdly fast, it is unordered, and its values are unique. But I'm just wondering, because HashSet<T> is a mutable class, so it has Add, Remove, etc.; and so I am not sure if the underlying data structure that makes these operations possible makes certain performance sacrifices when it comes to read operations -- in particular, I'm concerned with Contains. Basically, I'm wondering what are the absolute fastest-performing data structures in existence that can supply a Contains method for objects of type string. Within or outside of the .NET framework itself. I'm interested in all kinds of answers, regardless of their limitations. For example I can imagine that some structure might be restricted to strings of a certain length, or may be optimized depending on the problem domain (e.g., range of possible input values), etc. If it exists, I want to hear about it. One last thing: I'm not restricting this to read-only data structures. Obviously any read-write data structure could be embedded inside a read-only wrapper. The only reason I even mentioned the word "read-only" is that I don't have any requirement for a data structure to allow adding, removing, etc. If it has those functions, though, I won't complain.

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  • Import a number of csv files and replace NA by Zeros

    - by tao.hong
    I know how to do this individually. However, I have more than 1000 files. I decided to use a for loop. However, it seems like I did not find the correct way to evaluate my variables. Here is my code setwd('C:/data') filenames=dir() #find file names for (i in filenames){ adt = substr(x = i, start = 1, stop = nchar(i)-4) name=paste("data_", adt, sep="") assign(name, read.csv(i,header=T,sep=",")) #read each file and assign a variable name starting with data_ to it func=paste('name[is.na(name)] <- 0',sep="") # here is the place I have problem. R will not consider name is a parameter whose values change in each iteration eval((text=func)) }

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  • Declaring an integer Range with step != 1 in Ruby

    - by Dan Tao
    Hey guys, I'm completely new to Ruby, so be gentle. Say I want to iterate over the range of even numbers from 2 to 100; how would I do that? Obviously I could do: (2..100).each do |x| if x % 2 == 0 # my code end end But, obviously (again), that would be pretty stupid. I know I could do something like: i = 2 while i <= 100 # my code i += 2 end I believe I could also write my own custom class that provides its own each method (?). I am almost sure that would be overkill, though. I'm interested in two things: Is it possible to do this with some variation of the standard Range syntax (i.e., (x..y).each)? Either way, what would be the most idiomatic "Ruby way" of accomplishing this (using a Range or otherwise)? Like I said, I'm new to the language; so any guidance you can offer on how to do things in a more typical Ruby style would be much appreciated.

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