随机更改android布局背景

Question

I coded an activity that when user press only a button, the background would change randomly. I put background images in drawable file,and created a array of these images in value. Here is what i have got now:

 final LinearLayout background = (LinearLayout)findViewById(R.id.back);
 Button button = (Button)findViewById(R.id.button1);
 Resources res = getResources();
 final TypedArray myImages = res.obtainTypedArray(R.array.image);


    button.setOnClickListener(
            new Button.OnClickListener(){

       public void onClick(View v) {
        // TODO Auto-generated method stub 

   Random r = new Random(myImages.length()); 
   int b = r.nextInt();
  background.setBackgroundResource(b);


       }
                });

and the array:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <array name="image">
     <item>@drawable/background</item>
     <item>@drawable/background_blue</item>
     <item>@drawable/background_pink</item>
     <item>@drawable/background_orange</item>
     </array>
</resources>

It seems nothing wrong, but every time I start the emulator to check out, it always show that the activity stopped

can any one tell me what is the problem of my code?? I will appreciate that!!!

TO:Ashok logcat show these error

E/AndroidRuntime(802): FATAL EXCEPTION: main                 E/AndroidRuntime(802):java.lang.ArrayIndexOutOfBoundsException:length=456;index=1647793160
 E/AndroidRuntime(802):     at android.content.res.TypedArray.getResourceId(TypedArray.java:570)
 E/AndroidRuntime(802):     at com.example.cathy.MainActivity$1.onClick(MainActivity.java:39)
 E/AndroidRuntime(802):     at android.view.View.performClick(View.java:4240)
 E/AndroidRuntime(802):     at android.view.View$PerformClick.run(View.java:17721)
 E/AndroidRuntime(802):     at android.os.Handler.handleCallback(Handler.java:730)
 E/AndroidRuntime(802):     at android.os.Handler.dispatchMessage(Handler.java:92)
 E/AndroidRuntime(802):     at android.os.Looper.loop(Looper.java:137)
 E/AndroidRuntime(802):     atandroid.app.ActivityThread.main(ActivityThread.java:5103)
 E/AndroidRuntime(802):     at java.lang.reflect.Method.invokeNative(Native Method)
 E/AndroidRuntime(802):     at java.lang.reflect.Method.invoke(Method.java:525)
 E/AndroidRuntime(802):         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)

 E/AndroidRuntime(802):     atcom.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)

E/AndroidRuntime(802): at dalvik.system.NativeStart.main(Native Method)

Answer 1

Try this

final LinearLayout background = (LinearLayout) findViewById(R.id.back);
Button button = (Button) findViewById(R.id.button1);
Resources res = getResources();
final TypedArray myImages = res.obtainTypedArray(R.array.image);
final Random random = new Random();

button.setOnClickListener(new Button.OnClickListener() {

    public void onClick(View v) {

        //Genrate a random index in the range
        int randomInt = random.nextInt(myImages.length());

        // Generate the drawableID from the randomInt
        int drawableID = myImages.getResourceId(randomInt, -1);
        background.setBackgroundResource(drawableID);
    }
});

Answer 2

The problem is how you are using setBackgroundResource() . It expects the integer value of the resource file, not the array index.

Take a look here for how to get the value out of a resource array: Getting String Array From Resources

edit: Apologies, missed the beginning of your code. Try something like this:

background.setBackgroundResource(myImages.getResourceId(b,-1));

You might want to add error checking to see what getResourceId() returns first though.