Question

我在更改背景颜色时遇到问题。我想在活动开始后三秒钟更改它。我已经创建了一个计时器和一个处理程序+ runnable。当我想在三秒钟后更改一个特殊的EditText时它工作正常。但是当我添加行layout_interact.setBackgroundColor(Color.GREEN);并在虚拟设备中启动应用程序时，它会在启动包含计时器和处理程序的活动时崩溃。我还尝试在三秒钟后开始一项新活动，但结果却出现了同样的错误。这是我的代码：

public class ActivityInteractProcess extends Activity{
final Handler handler_interact=new Handler();//not defined as final variable. may cause problem
View layout_interact=(View) findViewById(R.id.layoutintprocess);

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.page_interact_process);


    //creating timer
    Timer timer_interact=new Timer();
    timer_interact.schedule(new TimerTask() {
          @Override
         public void run() {UpdateGUI();}
      }, 3000);
    }
   private void UpdateGUI() {
     handler_interact.post(runnable_interact);           
   }
    //creating runnable
   final Runnable runnable_interact = new Runnable() {
      public void run() {
      layout_interact.setBackgroundColor(Color.GREEN); //this is the line which makes the app Force close.
      }
   };
}

我还没有忘记将以下行添加到活动的xml布局中：

android:id="@+id/layoutintprocess"

以下是我在LogCat中遇到的错误：

AndroidRuntime(571): FATAL EXCEPTION: main
AndroidRuntime(571): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{aiLab.tests.autism/aiLab.tests.autism.ActivityInteractProcess}: java.lang.NullPointerException
AndroidRuntime(571):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1739)
AndroidRuntime(571):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
AndroidRuntime(571):    at android.app.ActivityThread.access$500(ActivityThread.java:122)  
AndroidRuntime(571):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
AndroidRuntime(571):    at android.os.Handler.dispatchMessage(Handler.java:99)
...

Answer 1

将您的代码更改为：

public class ActivityInteractProcess extends Activity{
final Handler handler_interact=new Handler();//not defined as final variable. may cause        problem
View layout_interact;

@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.page_interact_process);
layout_interact =(View) findViewById(R.id.layoutintprocess);


}


@Override
public void onWindowFocusChanged(boolean hasFocus) {
    super.onWindowFocusChanged(hasFocus);

    //creating timer
    Timer timer_interact=new Timer();
    timer_interact.schedule(new TimerTask() {
        @Override
        public void run() {UpdateGUI();}
    }, 3000);
}
private void UpdateGUI() {
    handler_interact.post(runnable_interact);
}
//creating runnable
final Runnable runnable_interact = new Runnable() {
    public void run() {
        layout_interact.setBackgroundColor(Color.GREEN);
    }
};
}

Answer 2

根据此article，您应使用 Handler 而不是 TaskTimer ，如下面的代码。

 private void updateGUI() {
    handler_interact.postDelayed(runnable_interact, 3000);
}

//creating runnable
final Runnable runnable_interact = new Runnable() {
    public void run() {
        layout_interact.setBackgroundColor(Color.GREEN); 
    }
};

Android - 在特定时间后更改背景颜色

2 个答案: