Can't create handler inside thread that has not called Looper.prepare() inside AsyncTask for ProgressDialog

问题

I don\'t understand why I\'m getting this error. I\'m using AsyncTask to run some processes in the background.

I have:

protected void onPreExecute() 
{
    connectionProgressDialog = new ProgressDialog(SetPreference.this);
    connectionProgressDialog.setCancelable(true);
    connectionProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
    connectionProgressDialog.setMessage(\"Connecting to site...\");
    connectionProgressDialog.show();

    downloadSpinnerProgressDialog = new ProgressDialog(SetPreference.this);
    downloadSpinnerProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
    downloadSpinnerProgressDialog.setMessage(\"Downloading wallpaper...\");
}

When I get into doInBackground() depending on a condition I:

[...]    
connectionProgressDialog.dismiss();
downloadSpinnerProgressDialog.show();
[...]

Whenever I try downloadSpinnerProgressDialog.show() I receive the error.

Any ideas guys?

回答1:

The method show() must be called from the User-Interface (UI) thread, while doInBackground() runs on different thread which is the main reason why AsyncTask was designed.

You have to call show() either in onProgressUpdate() or in onPostExecute().

For example:

class ExampleTask extends AsyncTask<String, String, String> {

    // Your onPreExecute method.

    @Override
    protected String doInBackground(String... params) {
        // Your code.
        if (condition_is_true) {
            this.publishProgress("Show the dialog");
        }
        return "Result";
    }

    @Override
    protected void onProgressUpdate(String... values) {
        super.onProgressUpdate(values);
        connectionProgressDialog.dismiss();
        downloadSpinnerProgressDialog.show();
    }
}

回答2:

I had a similar issue but from reading this question I figured I could run on UI thread:

YourActivity.this.runOnUiThread(new Runnable() {
    public void run() {
        alertDialog.show();
    }
});

Seems to do the trick for me.

回答3:

I had a hard time making this work too, the solution for me was to use both hyui and konstantin answers,

class ExampleTask extends AsyncTask<String, String, String> {

// Your onPreExecute method.

@Override
protected String doInBackground(String... params) {
    // Your code.
    if (condition_is_true) {
        this.publishProgress("Show the dialog");
    }
    return "Result";
}

@Override
protected void onProgressUpdate(String... values) {

    super.onProgressUpdate(values);
    YourActivity.this.runOnUiThread(new Runnable() {
       public void run() {
           alertDialog.show();
       }
     });
 }

}

回答4:

final Handler handler = new Handler() {
        @Override
        public void handleMessage(final Message msgs) {
        //write your code hear which give error
        }
        }

new Thread(new Runnable() {
    @Override
    public void run() {
    handler.sendEmptyMessage(1);
        //this will call handleMessage function and hendal all error
    }
    }).start();

来源：https://stackoverflow.com/questions/3614663/cant-create-handler-inside-thread-that-has-not-called-looper-prepare-inside-a

标签

java