android - 异步加载图像后，如何在 Recyclerview 中将项目 View 高度更改为图像高度？

Question

我的应用程序需要在列表回收 View 中按顺序显示大量图像，每个项目 View 都是一个 ImageView ，并且项目 View 的高度应该正好等于显示图像的高度，并且需要从网络加载图像。加载图片后似乎无法更改itemview的高度，出现NullPoint异常。有没有人遇到同样的问题？

这是代码:

recyclerView = (RecyclerView) findViewById(R.id.recycleView);
recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
recyclerView.setItemAnimator(new DefaultItemAnimator());
RecycleviewAdapter mRecycleviewAdapter = new RecycleviewAdapter(chData,chName,this);
recyclerView.setAdapter(mRecycleviewAdapter);

public class RecycleviewAdapter extends RecyclerView.Adapter<RecycleviewAdapter.MangaImageItemHolder> {

ChJs chJsonData;
String chName;
Context mContext;
int[] screenSize;
public RecycleviewAdapter(ChJs chJsonData, String chName, Context context){
    this.chJsonData = chJsonData;
    this.mContext = context;
    this.chName = chName;
    screenSize = Commons.getScreenSize(context);
}

@Override
public int getItemCount() {
    if(chJsonData!=null)
        return chJsonData.countOfPages();
    return 0;
}

@Override
public MangaImageItemHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    ImageView  mImageView = new ImageView(mContext);
    RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.MATCH_PARENT,
            RelativeLayout.LayoutParams.WRAP_CONTENT);
    mImageView.setLayoutParams(params);
    return new MangaImageItemHolder(mImageView, this);
}

@Override
public void onBindViewHolder(final MangaImageItemHolder holder, int position) {


    String imageName = ImangaFileManager.imageName(chName,
            String.valueOf(position));
    final String localImagePath = ImangaFileManager.localImagePath(MangaReader.website,
            MangaReader.mangaName, imageName, mContext);

    ExecutorService executorService = MangaReader.Executor4Local();

    executorService.execute(new Runnable() {

        @Override
        public void run() {
            BitmapFactory.Options op = new BitmapFactory.Options();
            op.inPreferredConfig = Bitmap.Config.RGB_565;
            final Bitmap bm = BitmapFactory.decodeFile(localImagePath, op);

            ((SherlockActivity)mContext).runOnUiThread(new Runnable() {
                @Override
                public void run() {

                    int height =  screenSize[0]*bm.getHeight()/bm.getWidth();
                    RecyclerView.LayoutParams params = new RecyclerView.LayoutParams(RecyclerView.LayoutParams.MATCH_PARENT,height);
                    holder.itemView.setLayoutParams(params);
                    holder.mImageView.setImageBitmap(bm);

                }
            });

        }
    });

}

public static class MangaImageItemHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    private ImageView mImageView;

    public MangaImageItemHolder(View itemView, RecycleviewAdapter adapter) {
        super(itemView);
        itemView.setOnClickListener(this);
        mImageView = (ImageView) itemView;
    }

    @Override
    public void onClick(View v) {
    }


}
}

LogCat:

 java.lang.NullPointerException
        at android.support.v7.widget.RecyclerView.findMinMaxChildLayoutPositions(RecyclerView.java:2537)
        at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:2324)
        at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:2709)
        at android.view.View.layout(View.java:14339)
        at android.view.ViewGroup.layout(ViewGroup.java:4612)
        at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1141)
        at android.view.View.layout(View.java:14339)
        at android.view.ViewGroup.layout(ViewGroup.java:4612)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:507)
        at android.view.View.layout(View.java:14339)
        at android.view.ViewGroup.layout(ViewGroup.java:4612)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:507)
        at android.view.View.layout(View.java:14339)
        at android.view.ViewGroup.layout(ViewGroup.java:4612)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:507)
        at android.view.View.layout(View.java:14339)
        at android.view.ViewGroup.layout(ViewGroup.java:4612)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2276)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2040)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1222)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5000)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:776)
        at android.view.Choreographer.doCallbacks(Choreographer.java:579)
        at android.view.Choreographer.doFrame(Choreographer.java:548)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:762)
        at android.os.Handler.handleCallback(Handler.java:800)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:194)
        at android.app.ActivityThread.main(ActivityThread.java:5463)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:854)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:621)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

您可以通过在适配器中应用元素的屏幕比例高度来实现。返回值的函数:

    public static int containerHeight(MainActivity ba) {

      DisplayMetrics dm = new DisplayMetrics();
      ba.getWindowManager().getDefaultDisplay().getMetrics(dm);

      //get predefined value
      double ratio = Static.PIC_RATIO_VALUE; //ex 4.0

      return (int) (dm.heightPixels / ratio); 
  }

在你的适配器(onBindViewHolder 模块)中你需要有类似的东西:

        //set height in proportion to screen size
        int proportionalHeight UIUtil.containerHeight((MainActivity)mCntx);
        TableRow.LayoutParams params = new TableRow.LayoutParams(TableRow.LayoutParams.MATCH_PARENT, proportionalHeight); // (width, height)
        holder.container.setLayoutParams(params);

holder.container 是您要应用高度逻辑的元素的根布局。

查看此 blog post ，您可以在其中获得有关如何实现此目标的更多详细信息。