Question

我想要创建的是一个水平滚动图库。我有一个RecyclerView（支持22.0.0）。我遇到的问题是，当我滚动到最后然后向后滚动时，通常会丢失一个图像，有时会丢失两个图像。奇怪的是，当我不停地来回扫动时，可能会丢失不同的图像。这是项目的布局：

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="160dp">

<ImageView
    android:id="@+id/product_variation_image"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:scaleType="centerCrop"
    android:layout_gravity="center"/>

这是Adaper：

public class TestAdapter extends RecyclerView.Adapter<TestAdapter.ViewHolder> {
private String[] mDataset;

public static class ViewHolder extends RecyclerView.ViewHolder {

    public ImageView mImageView;
    public ViewHolder(View v) {
        super(v);
        mImageView = (ImageView) v.findViewById(R.id.product_variation_image);
    }
}

public TestAdapter(String[] myDataset) {
    mDataset = myDataset;
}

@Override
public TestAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                               int viewType) {
    // create a new view
    View v = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.variaton_list_item, parent, false);
    ViewHolder vh = new ViewHolder(v);
    return vh;
}

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

    holder.mImageView.setImageDrawable(null);
    String url = mDataset[position];
    Log.i("TEST", "position = " + position);
    ((MainActivity)MainActivity.getInstance()).imageDownloader.download(url, holder.mImageView);
}

@Override
public int getItemCount() {
    return mDataset.length;
}

下载方法从URL获取图像，或者如果已经缓存，则从内存中获取图像。这适用于所有其他布局，例如ListView或GridView。以下是我用于在片段中设置它的代码：

    final LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
    layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
    mRecyclerView.setLayoutManager(layoutManager);

这是在onCreateView方法中。当我获取网址时，我填充它们并使用以下方式设置适配器：

  myDataset[i] = imageURL; // for each image       
  mAdapter = new TestAdapter(myDataset);
  mRecyclerView.setAdapter(mAdapter);

有趣的是适配器中onBindViewHolder方法中的行，我记录位置。我发现没有显示图像的单元格是没有调用此方法。就像它出于某种原因跳过那个单元格一样。更奇怪的是，如果我按住一个单元格并继续从左向右滑动，如果一个单元格离开屏幕然后重新进入，则其图像不再被调用onBindViewHolder方法。

Answer 1

我认为不重要的一个类是造成这个问题的一个类。我不知道原因是什么，但它存在于我用于从BitmapFun示例中获得的回收的自定义ImageView类中。

    public class RecyclingImageView extends ImageView {

    public RecyclingImageView(Context context) {
        super(context);
    }

    public RecyclingImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    /**
     * @see android.widget.ImageView#onAttachedToWindow()
     */
    @Override
    protected void onAttachedToWindow() {}

    /**
     * @see android.widget.ImageView#onDetachedFromWindow()
     */
    @Override
    protected void onDetachedFromWindow() {
        // This has been detached from Window, so clear the drawable

        setImageDrawable(null); 

        super.onDetachedFromWindow();
    }

    /**
     * @see android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)
     */
    @Override
    public void setImageDrawable(Drawable drawable) {
        // Keep hold of previous Drawable
        final Drawable previousDrawable = getDrawable();

        // Call super to set new Drawable
        super.setImageDrawable(drawable);

        // Notify new Drawable that it is being displayed
        notifyDrawable(drawable, true);

        // Notify old Drawable so it is no longer being displayed
        notifyDrawable(previousDrawable, false);
    }

    /**
     * Notifies the drawable that it's displayed state has changed.
     *
     * @param drawable
     * @param isDisplayed
     */
    private static void notifyDrawable(Drawable drawable, final boolean isDisplayed) {
        if (drawable instanceof RecyclingBitmapDrawable) {
            // The drawable is a CountingBitmapDrawable, so notify it
            ((RecyclingBitmapDrawable) drawable).setIsDisplayed(isDisplayed);
        } else if (drawable instanceof LayerDrawable) {
            // The drawable is a LayerDrawable, so recurse on each layer
            LayerDrawable layerDrawable = (LayerDrawable) drawable;
            for (int i = 0, z = layerDrawable.getNumberOfLayers(); i < z; i++) {
                notifyDrawable(layerDrawable.getDrawable(i), isDisplayed);
            }
        }
    }

}

当我用普通的ImageView替换它时，我不再遇到问题。

Answer 2

可以测试一下吗？您可以使用此库从URL加载图像吗？ http://square.github.io/picasso/它缓存所有内容，并以异步方式处理所有内容。

使用类似......

的东西

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

    Picasso.with(mImageView.getContext()).cancelRequest(holder.mImageView);

    String url = mDataset[position];
    Picasso.with(mImageView.getContext()).load(url).placeholder(R.drawable.placeholder).into(holder.mImageView);

}

...并查看它是否仍然不显示某些图像。如果确实如此，那么至少你会100％确定问题不在你的下载机制中（我认为可能是这样）。

如果您使用Android Studio，则只需添加相关性compile 'com.squareup.picasso:picasso:2.5.2'，否则您可以添加您在上述链接中找到的库。

值得一试......

Answer 3

我们可以通过扩展LinearLayoutManager和ImageView解决问题。

<强> 1。创建PrecachingLinearLayoutManager

public class PrecachingLinearLayoutManager extends LinearLayoutManager {

    private static final int DEFAULT_EXTRA_LAYOUT_SPACE = 600;

    private int extraLayoutSpace = -1;

    @SuppressWarnings("unused")
    private Context mContext;

    public PrecachingLinearLayoutManager(Context context) {
        super(context);
        this.mContext = context;
    }

    public PrecachingLinearLayoutManager(Context context, int extraLayoutSpace) {
        super(context);
        this.mContext = context;
        this.extraLayoutSpace = extraLayoutSpace;
    }

    public PrecachingLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
        this.mContext = context;
    }

    public void setExtraLayoutSpace(int extraLayoutSpace) {
        this.extraLayoutSpace = extraLayoutSpace;
    }

    @Override
    protected int getExtraLayoutSpace(RecyclerView.State state) {
        if (extraLayoutSpace > 0) {
            return (extraLayoutSpace);
        }
        return (DEFAULT_EXTRA_LAYOUT_SPACE);
    }
}

<强> 2。使用PrecachingLinearLayoutManager替换LinearLayoutManager

    DisplayMetrics displayMetrics = new DisplayMetrics();
    getActivity().getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
    PrecachingLinearLayoutManager layout = new PrecachingLinearLayoutManager(getActivity());
    layout.setExtraLayoutSpace(displayMetrics.heightPixels);
    recyclerview.setLayoutManager(layout);

第3。创建一个RecycleImageView

private Object tag = null;

@Override
protected void onAttachedToWindow() {
    Object tag = getTag();
    if (tag == null || !tag.equals(this.tag)) {
        // Will cause displayed bitmap wrapper to 
        // be 'free-able'
        setImageDrawable(null);
        this.tag = null;
        super.onDetachedFromWindow();
    }
    super.onAttachedToWindow();
}

@Override
protected void onDetachedFromWindow() {
    Object tag = getTag();
    if (tag != null) {
        this.tag = tag;
    } else {
        // Will cause displayed bitmap wrapper to 
        // be 'free-able'
        setImageDrawable(null);
        this.tag = null;
        super.onDetachedFromWindow();
    }
}

<强> 4。使用RecycleImageView替换ImageView

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:extends="http://schemas.android.com/apk/res/com.yourdomain.yourpackage"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/viewgroup"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<com.yourdomain.yourpackage.RecycleImageView
    android:id="@+id/photo"
    android:layout_width="40dp"
    android:layout_height="40dp"
    extends:delayable="true"
    android:contentDescription="@string/nothing"
    android:src="@drawable/photo_placeholder" >
</com.yourdomain.yourpackage.RecycleImageView>
</LinearLayout>

RecyclerView消失的图像

3 个答案: