Android中ImageSwitcher報NullPointerException,但ImageSwitcher中有值.解決辦法如下

     昨天在測試獲取手機SD卡中所有圖片中報ImageSwitcher空指針錯誤,但是打印出來的ImageSwitcher 中有值,很奇怪,改了很久.總算找出原因了.下面是錯誤代碼:

11-22 01:57:00.753: ERROR/AndroidRuntime(309): FATAL EXCEPTION: main11-22 01:57:00.753: ERROR/AndroidRuntime(309): java.lang.NullPointerException11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.widget.ImageSwitcher.setImageURI(ImageSwitcher.java:48)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at com.covics.gallery.HelloTakePhotoActivity.onItemSelected(HelloTakePhotoActivity.java:113)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.widget.AdapterView.fireOnSelected(AdapterView.java:864)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.widget.AdapterView.access$200(AdapterView.java:42)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:830)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.os.Handler.handleCallback(Handler.java:587)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.os.Handler.dispatchMessage(Handler.java:92)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.os.Looper.loop(Looper.java:123)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at android.app.ActivityThread.main(ActivityThread.java:4627)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at java.lang.reflect.Method.invokeNative(Native Method)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at java.lang.reflect.Method.invoke(Method.java:521)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)11-22 01:57:00.753: ERROR/AndroidRuntime(309): at dalvik.system.NativeStart.main(Native Method) 

他報的錯誤代碼如下所示:

	@Override
	public void onItemSelected(AdapterView<?> arg0, View arg1, int position,
			long id) {
		String url = listImages.get(position);
		System.out.println("url---->"+url);
		System.out.println("mImageSwitcher---->"+mImageSwitcher);
		System.out.println("uri---->"+Uri.parse(url));
		
		mImageSwitcher.setImageURI(Uri.parse(url));
	}

報空指針的是

		mImageSwitcher.setImageURI(Uri.parse(url));
	

改了很久,都沒弄出來,後來整體的再走了一遍流程,才發現錯誤所在:原來忘了爲ImageSwitcher添加一個容器:

mImageSwitcher.setFactory(this);

悲劇啊,所以以後大家代碼要寫仔細些啊,要不改起來好無語啊...

等我把程序全部完成了,再發出來和大家一起分享.

最後提醒下,一定要爲ImageSwitcher添加一個View.可以是ViewFactory也可以調用addView二次.