Implementing a while loop in android

问题:

I can't understand the implementation of a while loop in android.

Whenever I implement a while loop inside the onCreate() bundle, (code shown below)

public void onCreate(Bundle icicle) {       
  super.onCreate(icicle);
  setContentView(R.layout.main);
  TextView=(TextView)findViewById(R.id.TextView);
  while (testByte == 0)
      updateAuto(); 
}

nothing boots up, and the program enters a "hanging" state after a while and I can't understand why. Testbyte is as follows:

byte testByte == 0;

and updateAuto() is supposed to update the code per 1 second and display inside the textView portion. I've been using setText inside updateAuto() as shown below and everything works fine, but once i implement the while loop all i see is a black screen and then an option to force close after a few seconds due to it "not responding".

TextView.setText(updateWords);

I've changed it to a button format (meaning i have to click on the button to update itself for now), but i want it to update itself instead of manually clicking it.

Am i implementing the while loop in a wrong way?

I've also tried calling the while loop in a seperate function but it still gives me the black screen of nothingness.

I've been reading something about a Handler service... what does it do? Can the Handler service update my TextView in a safer or memory efficient way?

Many thanks if anyone would give some pointers on what i should do on this.

回答1:

Brace yourself. And try to follow closely, this will be invaluable as a dev.

While loops really should only be implemented in a separate Thread. A separate thread is like a second process running in your app. The reason why it force closed is because you ran the loop in the UI thread, making the UI unable to do anything except for going through that loop. You have to place that loop into the second Thread so the UI Thread can be free to run. When threading, you can't update the GUI unless you are in the UI Thread. Here is how it would be done in this case.

First, you create a Runnable, which will contain the code that loops in it's run method. In that Runnable, you will have to make a second Runnable that posts to the UI thread. For example:

 TextView myTextView = (TextView) findViewById(R.id.myTextView); //grab your tv
 Runnable myRunnable = new Runnable() {
      @Override
      public void run() {
           while (testByte == 0) {
                Thread.sleep(1000); // Waits for 1 second (1000 milliseconds)
                String updateWords = updateAuto(); // make updateAuto() return a string
                myTextView.post(new Runnable() { 
                     @Override
                     public void run() {
                          myTextView.setText(updateWords);
                     });
           }
      }
 };

Next just create your thread using the Runnable and start it.

 Thread myThread = new Thread(myRunnable);
 myThread.start();

You should now see your app looping with no force closes.