Why my button can trigger the UI to scroll and my TimerTask inside the activity can't?
- by Spidey
Long Story Short: a method of my activity updates and scrolls the ListView through an ArrayAdapter like it should, but a method of an internal TimerTask for polling messages (which are displayed in the ListView) updates the ListView, but don't scroll it. Why?
Long Story:
I have a chat activity with this layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#fff"
>
<ListView android:id="@+id/messageList"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:stackFromBottom="true"
android:transcriptMode="alwaysScroll"
android:layout_weight="1"
android:fadeScrollbars="true"
/>
<LinearLayout
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
>
<EditText android:id="@+id/message"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
/>
<Button android:id="@+id/button_send"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Send"
android:onClick="sendMessage"
/>
</LinearLayout>
</LinearLayout>
The internal listView (with id messageList) is populated by an ArrayAdapter which inflates the XML below and replaces strings in it.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:clickable="false"
android:background="#fff"
android:paddingLeft="2dp"
android:paddingRight="2dp"
>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/date"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="16sp"
android:textColor="#00F"
android:typeface="monospace"
android:text="2010-10-12 12:12:03"
android:gravity="left"
/>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/sender"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textSize="16sp"
android:textColor="#f84"
android:text="spidey"
android:gravity="right"
android:textStyle="bold"
/>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/body"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textSize="14sp"
android:padding="1dp"
android:gravity="left"
android:layout_below="@id/date"
android:text="Mensagem muito legal 123 quatro cinco seis."
android:textColor="#000"
/>
</RelativeLayout>
The problem is: in the main layout, I have a EditText for the chat message, and a Button to send the message. I have declared the adapter in the activity scope:
public class ChatManager extends Activity{
private EditText et;
private ListView lv;
private Timestamp lastDate = null;
private long campaignId;
private ChatAdapter ca;
private List<ChatMessage> vetMsg = new ArrayList<ChatMessage>();
private Timer chatPollingTimer;
private static final int CHAT_POLLING_PERIOD = 10000;
...
}
So, inside sendMessage(View v), the notifyDataSetChanged() scrolls the ListView acordingly, so I can see the latest chat messages automatically:
public void sendMessage(View v) {
String msg = et.getText().toString();
if(msg.length() == 0){
return;
}
et.setText("");
String xml = ServerCom.sendAndGetChatMessages(campaignId, lastDate, msg);
Vector<ChatMessage> vetNew = Chat.parse(new InputSource(new StringReader(xml)));
//Pegando a última data
if(!vetNew.isEmpty()){
lastDate = vetNew.lastElement().getDateSent();
//Atualizando a tela
vetMsg.addAll(vetNew);
ca.notifyDataSetChanged();
}
}
But inside my TimerTask, I can't. The ListView IS UPDATED, but it just don't scroll automatically. What am I doing wrong?
private class chatPollingTask extends TimerTask {
@Override
public void run() {
String xml;
if(lastDate != null){
//Chama o Updater
xml = ServerCom.getChatMessages(campaignId, lastDate);
}else{
//Chama o init denovo
xml = ServerCom.getChatMessages(campaignId);
}
Vector<ChatMessage> vetNew = Chat.parse(new InputSource(new StringReader(xml)));
if(!(vetNew.isEmpty())){
//TODO: descobrir porque o chat não está rolando quando chegam novas mensagens
//Descobrir também como forçar o rolamento, enquanto o bug não for corrigido.
Log.d("CHAT", "New message(s) acquired!");
lastDate = vetNew.lastElement().getDateSent();
vetMsg.addAll(vetNew);
ca.notifyDataSetChanged();
}
}
}
How can I force the scroll to the bottom? I've tried using scrollTo using lv.getBottom()-lv.getHeight(), but didn't work. Is this a bug in the Android SDK?
Sorry for the MASSIVE amount of code, but I guess this way the question gets pretty clear.
