android - 动态自动更改布局背景

Question

我有一个类似这样的布局。

xml

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/mylayout" > </RelativeLayout>

java - 然后您可以使用以下代码动态更改布局的背景

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        RelativeLayout relativeLayout = (RelativeLayout) findViewById(R.id.mylayout);
        int images[] = {R.drawable.image1, R.drawable.image2, R.drawable.image3, R.drawable.image4};

        relativeLayout.setBackgroundResource(images[getRandomNumber()]);
         private Timer myTimer;
         myTimer = new Timer();
         myTimer.schedule(new TimerTask() 
         {          
            @Override
            public void run() 
            {
                TimerMethod();
            }
         }, 0, 9000);
    }

private void TimerMethod()
           {
               new Handler().postDelayed(new Runnable() {

                @Override
                public void run() {

                    //TODO after 9 sec
                     relativeLayout.setBackgroundResource(images[getRandomNumber()]);
                }
            }, 9000);
        }
}

这是日志跟踪

01-04 01:08:15.307: E/AndroidRuntime(30200): FATAL EXCEPTION: Timer-0
01-04 01:08:15.307: E/AndroidRuntime(30200): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
01-04 01:08:15.307: E/AndroidRuntime(30200):    at android.os.Handler.<init>(Handler.java:121)
01-04 01:08:15.307: E/AndroidRuntime(30200):    at info.androidhive.slidingmenu.LoginActivity.TimerMethod(LoginActivity.java:55)
01-04 01:08:15.307: E/AndroidRuntime(30200):    at info.androidhive.slidingmenu.LoginActivity.access$0(LoginActivity.java:53)
01-04 01:08:15.307: E/AndroidRuntime(30200):    at info.androidhive.slidingmenu.LoginActivity$1.run(LoginActivity.java:48)
01-04 01:08:15.307: E/AndroidRuntime(30200):    at java.util.Timer$TimerImpl.run(Timer.java:284)

我想尝试的是在 Activity 时自动更改它。

Answer 1

onCreate() 仅在 Activity 首次打开时调用一次。离开后，onPause() 会被调用，稍后当您返回 Activity 时，onResume() 会被调用。

因此，要在每次导航到 Activity 时更改背景，请将代码从 onCreate() 更改为 onResume()。

public class MainActivity extends Activity {
RelativeLayout relativeLayout;
int images[];
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    relativeLayout = (RelativeLayout) findViewById(R.id.mylayout);
    images[]  = {R.drawable.image1, R.drawable.image2, R.drawable.image3, R.drawable.image4};     
}

protected void onResume()
{
    if(relativeLayout != null)
      relativeLayout.setBackgroundResource(images[getRandomNumber()]);

}

private int getRandomNumber() {
    //Note that general syntax is Random().nextInt(n)
    //It results in range 0-4
    //So it should be equal to number of images in images[] array
    return new Random().nextInt(4);
}}