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更改AsyncTask中自定义视图的可见性

android-custom-view android-asynctask android

Lyte · 技术社区 · 11 年前

我正在寻找一个关于在AsyncTask中更改自定义视图可见性的解决方案。我已经阅读了以下内容:

How to handle visibility changes for a custom android view/widget

但这对我没有帮助,因为我不知道如何处理界面。我已经将其放在自定义视图类中,但在哪里注册侦听器?在我有AsyncTask的活动中?方法应该是什么 onSetVisibilityCalled() 那么呢?

我希望你能帮助我,我感谢你的帮助。

代码段:

public Class MyActivity extends Activity{

private ProgressBar myProgressBar;
private MyCustomView myCustomView;
private MyTask myTask;

@Override
protected void onCreate(Bundle savedInstanceState) {

super(savedInstanceState);
    setContentView(R.layout.my_activity_layout.xml);
myProgressBar = (ProgressBar) findViewById(R.id.myProgressBar);
myCustomView = (MyCustomView) findViewById(R.id.myCustomView);
myTask = new MyTask();
myTask.execute();
}


private class MyTask extends AsyncTask<Void, Void, Void>{
protected void onPreExecute(){
myProgressBar.setVisibility(View.VISIBLE);

// Here I would like to change the visibility of my Custom View to GONE
// myCustomView.setVisibility(View.GONE);
}

@Override
protected void doInBackground(Void... params){
//... do something
}

protected void onPostExecute(){
myProgressBar.setVisibility(View.GONE);
// Here I would like to change the visibility of my Custom View to VISIBLE
// myCustomView.setVisibility(View.VISIBLE);
}
}
}

如果取消注释myCustomView.setVisibility(View.GONE);在onPreExecute()-方法中,我得到以下错误:

04-02 16:04:47.016:E/AndroidRuntime(322):致命异常:主04-02 16:04:47.016:E/AndroidRuntime(322):java.lang.RuntimeException: 无法启动活动 ComponentInfo{com.example.test/com.example.test.MyActivity}: java.lang.NullPointerException 04-02 16:04:47.016: E/AndroidRuntime(322):位于 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295) 04-02 16:04:47.016:E/AndroidRuntime(322):在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349) 04-02 16:04:47.016:E/AndroidRuntime(322):在 android.app.ActivityThread.access$700(ActivityThread.java:159)04-02 16:04:47.016:E/AndroidRuntime(322):在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316) 04-02 16:04:47.016:E/AndroidRuntime(322):在 android.os.Handler.dispatchMessage(Handler.java:99)04-02 16:04:47.016:E/AndroidRuntime(322):在 android.os.Looper.lop(Looper.java:176)04-02 16:04:47.016: E/AndroidRuntime(322):位于 android.app.ActivityThread.main(ActivityThread.java:5419)04-02 16:04:47.016:E/AndroidRuntime(322):在 java.lang.reflect.Method.invokeNative(本机方法)04-02 16:04:47.016:E/AndroidRuntime(322):在 java.lang.reflect.Method.invoke(Method.java:525)04-02 16:04:47.016: E/AndroidRuntime(322):位于 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046) 04-02 16:04:47.016:E/AndroidRuntime(322):在 com.android.internal.os.ZygoteInit.main(ZygoteIndit.java:862)04-02 16:04:47.016:E/AndroidRuntime(322):在 dalvik.system.NativeStart.main(本地方法)04-02 16:04:47.016: E/AndroidRuntime(322):由java.lang.NullPointerException 04-02引起 16:04:47.016:E/AndroidRuntime(322):在 com.example.test.MyActivity$FetchLocationTask.onPreExecute(MyActivity.java:55) 04-02 16:04:47.016:E/AndroidRuntime(322):在 android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)04-02 16:04:47.016:E/AndroidRuntime(322):在 android.os.AsyncTask.execute(AsyncTask.java:534)04-02 16:04:47.016: E/AndroidRuntime(322):位于 com.example.test.MyActivity.onCreate(MyActivity.java:32)04-02 16:04:47.016:E/AndroidRuntime(322):在 android.app.Activity.performCreate(Activity.java:5372)04-02 16:04:47.016:E/AndroidRuntime(322):在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104) 04-02 16:04:47.016:E/AndroidRuntime(322):在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257) 04-02 16:04:47.016:E/AndroidRuntime(322):。。。还有11个

2 回复 | 直到 8 年前

Drew 11 年前

您的问题不在AsyncTask中。在您的 onCreate(Bundle) 你没有的方法 setContentView(int) .

假设ProgressBar和MyCustomView在 您的活动布局.xml 资源文件,应添加一行: setContentView(R.layout.your_activity_layout.xml) .

在呼叫后立即将其添加到 super(Bundle) 构造函数(您也忘了添加它):

@Override
protected void onCreate(Bundle savedInstanceState) {
    super(savedInstanceState);//you forgot that
    setContentView(R.layout.your_activity_layout.xml);//and that
    myProgressBar = (ProgressBar) findViewById(R.id.myProgressBar);
    myCustomView = (MyCustomView) findViewById(R.id.myCustomView);
    ...
}

现在你们两个 View s不应为空(如果它们存在于xml布局文件中),并且上面的代码应该有效。

sadegh saati 11 年前

您不需要以这种方式处理可见性。如果您只需要更改可见性,只需调用您的view.setVisibility,如果您希望在自定义视图中调用override setVisibility并首先调用super.setVisibilty,那么您需要这样做。