Why Does Incorrect Use of Android's `runOnUiThread` Lead to Unresponsive UI?

Understanding runOnUiThread in Android

In Android development, the UI thread is responsible for handling user interactions and updating the user interface. To ensure that all UI operations are performed on the UI thread, the runOnUiThread method is commonly used.

In your provided code snippet, an attempt is made to update the UI within a separate thread using runOnUiThread. However, the current implementation is incorrect, leading to unresponsive behavior upon button click. Here's why:

Incorrect Usage of runOnUiThread

The runOnUiThread method accepts a Runnable instance as its argument. In your code, you're erroneously creating a new thread via Thread(Runnable) instead of implementing the runnable in the current activity. This results in creating a separate thread without a looper, which is essential for handling UI events.

Corrected Code

The corrected version of the runThread method is as follows:

private void runThread() {

    new Thread() {
        public void run() {
            while (i++ < 1000) {
                try {
                    runOnUiThread(new Runnable() {

                        @Override
                        public void run() {
                            btn.setText("#" + i);
                        }
                    });
                    Thread.sleep(300);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }.start();
}

In this corrected code, a new thread is created, but within that thread, runOnUiThread is invoked to update the UI elements on the UI thread. The Runnable instance passed to runOnUiThread contains the code that updates the button's text.

By using runOnUiThread correctly, you ensure that all UI-related operations occur on the main UI thread, preventing UI freezes and ensuring responsiveness.

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