问题
I'm busy with making an app for an android device. And now I'm testing with some things.
I want to change the background color limited times, lets say 5. Every time the background's changed, I want it to change again after 2-3 seconds.
If I am using the Thread class, it loads the whole template after the Thread has finished, you can't see the color changes, but they're running in the "background" (I can see that in LogCat).
I hope that there is a tutorial or an example that I can use.
Thanks!
回答1:
I recently learned how to do this. There is a good tutorial here: http://www.vogella.com/articles/AndroidPerformance/article.html#handler
It's a little tricky at first, you're executing on the main thread, you start a sub-thread, and post back to the main thread.
I made this small activity to flash buttons on and off to make sure I know what's going on:
public class HelloAndroidActivity extends Activity {
/** Called when the activity is first created. */
Button b1;
Button b2;
Handler myOffMainThreadHandler;
boolean showHideButtons = true;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
myOffMainThreadHandler = new Handler(); // the handler for the main thread
b1 = (Button) findViewById(R.id.button1);
b2 = (Button) findViewById(R.id.button2);
}
public void onClickButton1(View v){
Runnable runnableOffMain = new Runnable(){
@Override
public void run() { // this thread is not on the main
for(int i = 0; i < 21; i++){
goOverThereForAFew();
myOffMainThreadHandler.post(new Runnable(){ // this is on the main thread
public void run(){
if(showHideButtons){
b2.setVisibility(View.INVISIBLE);
b1.setVisibility(View.VISIBLE);
showHideButtons = false;
} else {
b2.setVisibility(View.VISIBLE);
b1.setVisibility(View.VISIBLE);
showHideButtons = true;
}
}
});
}
}
};
new Thread(runnableOffMain).start();
}
private void goOverThereForAFew() {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
回答2:
Use handlers in your UI thread:
Handler mHandler = new Handler();
Runnable codeToRun = new Runnable() {
@Override
public void run() {
LinearLayout llBackground = (LinearLayout) findViewById(R.id.background);
llBackground.setBackgroundColor(0x847839);
}
};
mHandler.postDelayed(codeToRun, 3000);
Handlers will run whatever code you'd like, on the UI thread, after a specified amount of time.
来源：https://stackoverflow.com/questions/10965291/update-ui-with-thread-sleep