Null point exception in IMageSwitcher.setImageResource()

问题

I am doing an animation to show many images in ImageSwitcher but am stuck in setting images to ImageSwitcher.

This is the imageswitcher in my xml.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_margin="10dp"
        android:src="@drawable/logo" />

    <ImageSwitcher
        android:id="@+id/switcher"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </ImageSwitcher>

</LinearLayout>

and here is my code

setContentView(R.layout.main_screen);

    final int[] imgs = {R.drawable.m1,
        R.drawable.m2,
        R.drawable.m3,
        R.drawable.m4,
        R.drawable.m5,
        R.drawable.m6};

    imgswitcher = (ImageSwitcher) findViewById(R.id.switcher);
    imgswitcher.postDelayed(new Runnable() 
    {
        int index = 0;
        @Override
        public void run() 
        {
            imgswitcher.setImageResource(imgs[index]);
            if(index==(imgs.length-1))
                 index = 0;
            else
                 index++;
            imgswitcher.postDelayed(this, 1000);
        }
    }, 1000);

I am getting error on line "imgswitcher.setImageResource(imgs[index]);"

Error

11-13 15:08:34.574: E/AndroidRuntime(5258): FATAL EXCEPTION: main
11-13 15:08:34.574: E/AndroidRuntime(5258): java.lang.NullPointerException
11-13 15:08:34.574: E/AndroidRuntime(5258):     at android.widget.ImageSwitcher.setImageResource(ImageSwitcher.java:41)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at com.example.imageswitcher.MainActivity$1.run(MainActivity.java:33)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at android.os.Handler.handleCallback(Handler.java:587)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at android.os.Handler.dispatchMessage(Handler.java:92)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at android.os.Looper.loop(Looper.java:123)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at android.app.ActivityThread.main(ActivityThread.java:3683)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at java.lang.reflect.Method.invokeNative(Native Method)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at java.lang.reflect.Method.invoke(Method.java:507)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
11-13 15:08:34.574: E/AndroidRuntime(5258):     at dalvik.system.NativeStart.main(Native Method)

I even tried it without the Runnable just assigning a drawable to ImageSwitcher, but am facing the same issue. Any help would be appreciated.

回答1:

imgswitcher.setFactory(this);

is missing

Edit Further solution is given by question author:

public MyActivity implements ViewSwitcher.ViewFactory

@Override
public View makeView() {
    ImageView imageView = new ImageView(this);
    imageView.setBackgroundColor(0xFF000000);
    imageView.setScaleType(ImageView.ScaleType.CENTER);
    imageView.setLayoutParams(
        new ImageSwitcher.LayoutParams(
            LayoutParams.MATCH_PARENT,
            LayoutParams.WRAP_CONTENT));
    return imageView;
}

There are alternatives to setting a factory with setFactory. Read the ViewSwitcher docs.

回答2:

I hope it helps.

Override onViewCreated Method and put your ImageSwitcher inside it. i.e.

public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    mImageSwitcher.setImageResource(image[index]);

}

回答3:

that is because you need to call imageSwitcher.setFacotry on the imageSwitcher before any call to imageSwitcher.setImageResource , just use the code below :

 imageSwitcher.setFactory(new ViewFactory() {
       public View makeView() {
          ImageView myView = new ImageView(getApplicationContext());
          return myView;
       }
    }
//then you can call setImageResource
imageSwitcher.setImageResource(R.drawable.my_image);

来源：https://stackoverflow.com/questions/19950344/null-point-exception-in-imageswitcher-setimageresource

标签

android

drawable

android-image

imageswitcher