java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare(); [duplicate]

Answer 1

I got this exception because I was trying to make a Toast popup from a background thread.
Toast needs an Activity to push to the user interface and threads don't have that.
So one workaround is to give the thread a link to the parent Activity and Toast to that.

Put this code in the thread where you want to send a Toast message:

parent.runOnUiThread(new Runnable() {
    public void run() {
        Toast.makeText(parent.getBaseContext(), "Hello", Toast.LENGTH_LONG).show();
    }
});

Keep a link to the parent Activity in the background thread that created this thread. Use parent variable in your thread class:

private static YourActivity parent;

When you create the thread, pass the parent Activity as a parameter through the constructor like this:

public YourBackgroundThread(YourActivity parent) {
    this.parent = parent;
}

Now the background thread can push Toast messages to the screen.