CODEWITHSUNDEEP
androidmultithreadinghandler
fredley
fredley

Reputation: 33861

Android Handler problem

I'm sure I'm doing something stupid here, but the following code:

...

public void onClick(View v) {
  extractThread et = new extractThread();
  et.start();
}

...

private class extractThread extends Thread{

  public void run(){
    expensiveOperation();

    Message m = new Message();
    Bundle b = new Bundle();
    b.putString("message","result");
    m.setData(b);
    extractHandler.dispatchMessage(m);
    }
}

private Handler extractHandler = new Handler(){

  public void handleMessage(Message m){

    Bundle b = m.getData();
    String message = b.getString("message");

    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setMessage(message)
        .setCancelable(false)
        .setPositiveButton("OK", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.cancel();
              }
    });
    builder.create().show();
  }
};

is still getting 

01-07 11:55:02.791: ERROR/AndroidRuntime(18791): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

at the line builder.create().show();, despite the fact this is called inside a Handler in my main thread inside handleMessage. What am I doing wrong?

Upvotes: 0

Views: 2438

Answers (2)

dave.c
dave.c

Reputation: 10908

Is the code you posted within your Activity class?

I would also use

Message msg = Message.obtain();

rather than creating a new message. Also if you just want to pass a String then:

private static final int HANDLER_MESSAGE_RESULT = 0;
...
msg.what = HANDLER_MESSAGE_RESULT;
msg.obj = "result";

is more efficient than passing a Bundle. In your Handler you can then switch on the what which allows you to add new message types in the future. I think you should also be using:

extractHandler.sendMessage(m);

rather than 

extractHandler.dispatchMessage(m);

Not sure that any of that fixes your issue though!

Upvotes: 2

fredley
fredley

Reputation: 33861

Yes, it was something stupid. I should have used extractHandler.sendMessage(m); instead of extractHandler.dispatchMessage(m);

Upvotes: 1

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