Changing visibility of custom view within an AsyncTask

StackOverflow https://stackoverflow.com/questions/22812345

Question

I am searching for a solution on changing the visibility of my custom view within an AsyncTask. I have read this:

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

But it doesn't help me since I don't get how to handle the Interface. I've put this in my Custom View Class, but where do I register the listener? In the Activity where I have my AsyncTask? And what should the method onSetVisibilityCalled() do then?

I hope you can help me and I appreciate your help.

Code snippet:

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);
}
}
}

If i uncomment myCustomView.setVisibility(View.GONE); in the onPreExecute()-Method I get following errors:

04-02 16:04:47.016: E/AndroidRuntime(322): FATAL EXCEPTION: main 04-02 16:04:47.016: E/AndroidRuntime(322): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.MyActivity}: java.lang.NullPointerException 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.ActivityThread.access$700(ActivityThread.java:159) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.os.Handler.dispatchMessage(Handler.java:99) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.os.Looper.loop(Looper.java:176) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.ActivityThread.main(ActivityThread.java:5419) 04-02 16:04:47.016: E/AndroidRuntime(322): at java.lang.reflect.Method.invokeNative(Native Method) 04-02 16:04:47.016: E/AndroidRuntime(322): at java.lang.reflect.Method.invoke(Method.java:525) 04-02 16:04:47.016: E/AndroidRuntime(322): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046) 04-02 16:04:47.016: E/AndroidRuntime(322): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862) 04-02 16:04:47.016: E/AndroidRuntime(322): at dalvik.system.NativeStart.main(Native Method) 04-02 16:04:47.016: E/AndroidRuntime(322): Caused by: java.lang.NullPointerException 04-02 16:04:47.016: E/AndroidRuntime(322): at com.example.test.MyActivity$FetchLocationTask.onPreExecute(MyActivity.java:55) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.os.AsyncTask.execute(AsyncTask.java:534) 04-02 16:04:47.016: E/AndroidRuntime(322): at com.example.test.MyActivity.onCreate(MyActivity.java:32) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.Activity.performCreate(Activity.java:5372) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104) 04-02 16:04:47.016: E/AndroidRuntime(322): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257) 04-02 16:04:47.016: E/AndroidRuntime(322): ... 11 more

Was it helpful?

Solution

Your problem is not in AsyncTask. In your onCreate(Bundle) method you did not setContentView(int).

Assuming that your ProgressBar and MyCustomView are defined in your_activity_layout.xml resource file, you should add a line: setContentView(R.layout.your_activity_layout.xml).

Add it just after the call to super(Bundle) constructor (you forgot to add it,too):

@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);
    ...
}

Now both of your Views should be not null (if they present in xml layout file), and the above code should work.

OTHER TIPS

you do not need to handle visibility in this way.if you just need to change visibility just call yourview.setVisibility and if you want to be informed if this called override setVisibility in your custom view and call super.setVisibilty at first then do want you need to do.

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