尝试用资源填充ImageSwitcher
时,我不断收到NullPointerException错误。在WeakReference
期间,使用AsyncTask
中的onPreExecute()
调用它:
if (imageSwitcherReference != null) {
ImageSwitcher imageSwitcher = imageSwitcherReference.get();
if (imageSwitcher != null) {
imageSwitcher.setImageResource(R.drawable.receta_nofoto);
}
}
这是预堆栈跟踪:
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): java.lang.NullPointerException
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.widget.ImageSwitcher.setImageResource(ImageSwitcher.java:41)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at com.paravegetarianos.motores.DescargadorImagenes.onPreExecute(DescargadorImagenes.java:90)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.os.AsyncTask.execute(AsyncTask.java:391)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at com.paravegetarianos.FotosGaleria.seleccionarImagen(FotosGaleria.java:57)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at com.paravegetarianos.FotosGaleria.access$0(FotosGaleria.java:53)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at com.paravegetarianos.FotosGaleria$1.onItemSelected(FotosGaleria.java:43)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.widget.AdapterView.fireOnSelected(AdapterView.java:864)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.widget.AdapterView.access$200(AdapterView.java:42)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:830)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.os.Handler.handleCallback(Handler.java:587)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.os.Handler.dispatchMessage(Handler.java:92)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.os.Looper.loop(Looper.java:123)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at android.app.ActivityThread.main(ActivityThread.java:4627)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at java.lang.reflect.Method.invokeNative(Native Method)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at java.lang.reflect.Method.invoke(Method.java:521)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
02-21 16:13:10.639: ERROR/AndroidRuntime(4274): at dalvik.system.NativeStart.main(Native Method)
尝试使用我之前创建的BitmapDrawable设置Drawable时,它也变成NullPointerException。
if (imageSwitcherReference != null) {
ImageSwitcher imageSwitcher = imageSwitcherReference.get();
if (imageSwitcher != null) {
BitmapDrawable bm = new BitmapDrawable(result);
imageSwitcher.setImageDrawable(bm);
}
}
结果是在
onPostExecute()
步骤中捕获了位图。我调用AsyncTask的时刻是在构建Gallery的onItemSelectedListener()时: galeria.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
seleccionarImagen(arg2);
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
seleccionarImagen(0);
}
});
其中galeria是Gallery,而
seleccionarImagen(int)
获取图像索引并调用AsyncTask。这是post stacktrace(在注释错误行之后):
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): FATAL EXCEPTION: main
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): java.lang.NullPointerException
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at android.widget.ImageSwitcher.setImageDrawable(ImageSwitcher.java:55)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at com.paravegetarianos.motores.DescargadorImagenes.onPostExecute(DescargadorImagenes.java:66)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at com.paravegetarianos.motores.DescargadorImagenes.onPostExecute(DescargadorImagenes.java:1)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at android.os.AsyncTask.finish(AsyncTask.java:417)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at android.os.AsyncTask.access$300(AsyncTask.java:127)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at android.os.Handler.dispatchMessage(Handler.java:99)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at android.os.Looper.loop(Looper.java:123)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at android.app.ActivityThread.main(ActivityThread.java:4627)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at java.lang.reflect.Method.invokeNative(Native Method)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at java.lang.reflect.Method.invoke(Method.java:521)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
02-21 16:04:42.849: ERROR/AndroidRuntime(4201): at dalvik.system.NativeStart.main(Native Method)
您可以通过此代码找到任何(我敢打赌这将是一个非常愚蠢且明显的错误)问题吗?谢谢大家。
PS:错误行(66和90)是setImageDrawable和setImageResource的调用位置。如果您认为需要更多代码,请告诉我,我将其附加。
最佳答案
您需要通过设置ImageSwitcher
或两次调用ViewFactory
将视图添加到addView
中。 docs for ViewSwitcher中的更多信息。
例如,查看问题中的最后一个堆栈跟踪,NPE发生在ImageSwitcher.java的第55行,即:
public void setImageDrawable(Drawable drawable)
{
ImageView image = (ImageView)this.getNextView();
image.setImageDrawable(drawable); // <--- line 55
showNext();
}
image
为null,因为尚未设置视图。关于android - ImageSwitcher中的setImageDrawable和setImageResource时发生NullPointerException,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/5067677/