contextthemewrapper不能转换为活动

Question

在我的小应用程序中,我有一个PageAdapter-> Fragment-> ListView-> ImageView.在onImageClick上我希望在另一个片段(Fragment3)中显示我的图像,但是当我在Fragment3中加载图像时会得到一个例外

public class Fragment3 extends DialogFragment {
ImageLoader imageLoader;
...
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    view = (ViewGroup) inflater.inflate(R.layout.fragment3_layout, container, false);
    imageView = (ImageView) view.findViewById(R.id.imageViewFrag3);
    detail = (TextView) view.findViewById(R.id.textViewFrag3);
    imageUrl = getArguments().getString("URL");
    imageView.setTag(imageUrl); 
    activity=this;      
    imageLoader = new ImageLoader(activity.getActivity().getApplicationContext());      
    imageLoader.DisplayImage(imageUrl, (Activity) activity.getActivity(), imageView);       
    return view;
}
...
}

和创建异常的代码.当我创建一个片段并添加ListView时,所有传递确定,但是当我创建另一个片段(子)并想要加载Photo时它失败了.

代码,如何创建子片段,没有PageAdapter

holder.imgViewImage = (ImageView) vi.findViewById(R.id.imageView01);
        holder.imgViewImage.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {                   
                android.support.v4.app.FragmentTransaction ft = activity.getFragmentManager().beginTransaction();                   
                Fragment3 newFragment = Fragment3.newInstance();                    
                Bundle bundle=new Bundle();
                bundle.putString("URL", holder.imgViewImage.getTag().toString());
                newFragment.setArguments(bundle);
                newFragment.show( ft, "dialog");
                Log.i("!!!", "Click on image");                 
            }
        })

这是Photo Loader Thread,

class PhotosLoader extends Thread {
    public void run() {
        try {
            while(true)
            {
                if(photosQueue.photosToLoad.size()==0)
                    synchronized(photosQueue.photosToLoad){
                        photosQueue.photosToLoad.wait();
                    }
                if(photosQueue.photosToLoad.size()!=0)
                {
                    PhotoToLoad photoToLoad;
                    synchronized(photosQueue.photosToLoad){
                        photoToLoad=photosQueue.photosToLoad.pop();
                    }
                    Bitmap bmp=getBitmap(photoToLoad.url);
                    cache.put(photoToLoad.url, bmp);
                    if(((String)photoToLoad.imageView.getTag()).equals(photoToLoad.url)){
                        BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad.imageView);            
                        //Exception contextthemewrapper cannot be cast to activity !!!
                        Activity a= (Activity)(photoToLoad.imageView.getContext());
                        a.runOnUiThread(bd);
                    }
                }
                if(Thread.interrupted())
                    break;
            }
        } catch (InterruptedException e) {
        }
    }
}

和例外

02-09 08:22:57.510: E/AndroidRuntime(1449): FATAL EXCEPTION: Thread-114
02-09 08:22:57.510: E/AndroidRuntime(1449): java.lang.ClassCastException: android.view.ContextThemeWrapper cannot be cast to android.app.Activity
02-09 08:22:57.510: E/AndroidRuntime(1449):     at com.example.ids.ImageLoader$PhotosLoader.run(ImageLoader.java:171)

Answer 1

我有类似的情况.可能是相关问题> 从自定义按钮访问活动

我用这个片段解决了我的问题.

private static Activity scanForActivity(Context cont) {
    if (cont == null)
        return null;
    else if (cont instanceof Activity)
        return (Activity)cont;
    else if (cont instanceof ContextWrapper)
        return scanForActivity(((ContextWrapper)cont).getBaseContext());

    return null;
}

Answer 2

Activity a= (Activity)(photoToLoad.imageView.getContext());

你不能假设一个Context可以被铸造成一个Activity.因此,异常:您正在尝试蒙上了Context那其实是一个ContextThemeWrapper到Activity.

你可以替换

Activity a= (Activity)(photoToLoad.imageView.getContext());
a.runOnUiThread(bd);

用例如

photoToLoad.imageView.post(bd);

发布一个Runnable到UI线程消息队列,类似于Activity runOnUiThread().

Answer 3

据我所知，如果一个View显示在Dialog中，它的上下文（从view.getContext()访问）实际上是一个ThemeContextWrapper实例，它可能不是一个Activity。要从 Dialog 获取 Activity，可以使用 getOwnerActivity()，它返回 Dialog 所属的 Activity。