CODEWITHSUNDEEP
androidandroid-viewandroid-handler
dev
dev

Reputation: 11309

What is the difference between view.post() and view.getHandler().post() on Android?

Documentation about view.post() says:

Causes the Runnable to be added to the message queue. The runnable will be run on the user interface thread.

view.getHandler() returns the following:

A handler associated with the thread running the View.

I understand views can be created in a background thread, but they will always run on the UI thread. Which implies view.getHandler() should always return a handler associated with UI thread - essentially making view.getHandler().post() and view.post() posting to the same MessageQueue.

Why should I ever use view.getHandler().post() ?

Upvotes: 0

Views: 1460

Answers (1)

OneCricketeer
OneCricketeer

Reputation: 191738

There isn't much difference other than getHandler().post() can throw you to a NullPointerException since it can return null. 

/**
 * @return A handler associated with the thread running the View. This
 * handler can be used to pump events in the UI events queue.
 */
public Handler getHandler() {
    final AttachInfo attachInfo = mAttachInfo;
    if (attachInfo != null) {
        return attachInfo.mHandler;
    }
    return null;
}

Meanwhile, this simply redirects under the same conditions, but returns a boolean. 

/**
 * <p>Causes the Runnable to be added to the message queue.
 * The runnable will be run on the user interface thread.</p>
 *
 * @param action The Runnable that will be executed.
 *
 * @return Returns true if the Runnable was successfully placed in to the
 *         message queue.  Returns false on failure, usually because the
 *         looper processing the message queue is exiting.
 *
 * @see #postDelayed
 * @see #removeCallbacks
 */
public boolean post(Runnable action) {
    final AttachInfo attachInfo = mAttachInfo;
    if (attachInfo != null) {
        return attachInfo.mHandler.post(action);
    }

    // Postpone the runnable until we know on which thread it needs to run.
    // Assume that the runnable will be successfully placed after attach.
    getRunQueue().post(action);
    return true;
}

Upvotes: 3

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