从 TimerTask 的运行方法更新 TextView 时出错

Question

I'm trying to test UI and Timer class possibilities. So I tried the following exercise:

=== TestTimerActivity.java ===

package com.tvt.TestTimer;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import java.util.Timer;
import java.util.TimerTask;


public class TestTimerActivity extends Activity {
    TextView _tv;
    Timer _t;
    int _count = 0;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        //

//        _tv = (TextView) getWindow().getDecorView().findViewById( R.id.TextViewTime );

        _tv = (TextView) findViewById( R.id.TextViewTime );

        UpdateTime(); // Completes OK

        _t = new Timer();

        _t.scheduleAtFixedRate( new TimerTask() {
            @Override
            public void run() {
                // TODO Auto-generated method stub
                _count++;
                UpdateTime(); // Fails
            }
        }, 1000, 1000 );
    }

    protected void UpdateTime() {
        _tv.setText( "" + _count );
    }
}

=== TestTimerActivity.java ===

=== main.xml ===

<?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"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:gravity="center_horizontal" android:layout_height="wrap_content" android:layout_gravity="center" android:text="@string/header" android:id="@+id/TestViewHeader" android:textStyle="bold"/>
<TextView android:layout_height="wrap_content" android:id="@+id/TextViewTime" android:layout_width="match_parent" android:layout_gravity="center_horizontal" android:gravity="center_horizontal" android:text="-"></TextView>
</LinearLayout>

=== main.xml ===

The very first UpdateTime call (from onCreate) completes OK but the same call from TimerTask::run() fails giving the message "TestTimer class has stopped unexpectedly".

Any idea? Where is my fault?

--
SY, TVT

Answer 1

Do that UpateTime() operation on the UI thread.

protected void UpdateTime() 
{
     runOnUiThread(new Runnable() 
     {
    public void run() 
    {
            _tv.setText( "" + _count );
        }
     });
}

Hopefully resolves your problem.

Answer 2

Updating the UI from a thread other than the UI/main thread will fail as Android does not allow it. Try using a Handler to post messages back to the UI thread.

Or maybe try using AsyncTask which presents a set of really simple callback methods to handle the worker and UI threads. But that might not be exactly what you need since you're trying to test out the TimerTask class.