RecyclerView 延迟加载（通用图像加载器）

Question

使用Android Universal Image Loader 和 RecyclerView 异步加载图像，我遇到了和其他人一样的错误，图像混淆了；直到它们全部加载并被缓存。

适配器代码：

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.DialogInterface;
import android.graphics.Bitmap;
import android.media.Image;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.ImageView;
import android.widget.TextView;

import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.assist.FailReason;
import com.nostra13.universalimageloader.core.listener.ImageLoadingListener;
import com.nostra13.universalimageloader.core.listener.SimpleImageLoadingListener;
import com.nostra13.universalimageloader.utils.MemoryCacheUtils;

import java.net.URI;
import java.net.URISyntaxException;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import romina.theftest.connectivity.ImgDownloader;

/**
 * Created by romin on 18/1/2016.
 */
public class ProductRecyclerViewAdapter extends RecyclerView.Adapter {
    private List<Product> mValues;
    private Context mContext;
    private View.OnClickListener mListener;
    // Allows to remember the last item shown on screen
    private int lastPosition = -1;
    private final String OLD_DOMAIN = "";
    private final String NEW_DOMAIN = "";

    public ProductRecyclerViewAdapter(Context mContext, View.OnClickListener mListener) {
        this.mContext = mContext;
        this.mListener = mListener;
    }

    public ProductRecyclerViewAdapter(List<Product> mValues, Context mContext, View.OnClickListener mListener) {
        this(mContext, mListener);
        this.mListener = mListener;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.product_list_item, parent, false);

        Log.d(ProductRecyclerViewAdapter.class.getSimpleName(), "onCreateViewHolder");
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        ViewHolder actualViewHolder = (ViewHolder) holder;
        actualViewHolder.mItem = mValues.get(position);
        actualViewHolder.mIdView.setText("" + mValues.get(position).getName());
        Log.d(ProductRecyclerViewAdapter.class.getSimpleName(), "onBindViewHolder pos " + position);

        ImageLoader imageLoader = ImageLoader.getInstance(); // Get singleton instance
        final String finalImgURL = mValues.get(position).getImgURL().toString().replaceAll(OLD_DOMAIN, NEW_DOMAIN);
            imageLoader.displayImage(finalImgURL, actualViewHolder.mImgView);

        setAnimation(actualViewHolder.mContentView, position);
    }

    public void setDataSet(List<Product> newValues) {
        mValues = newValues;
        notifyDataSetChanged();
    }


    @Override
    public int getItemCount() {
        return mValues == null ? 0 : mValues.size();
    }

    /**
     * Here is the key method to apply the animation
     */
    private void setAnimation(View viewToAnimate, int position) {
        // If the bound view wasn't previously displayed on screen, it's animated
        if (position > lastPosition) {
            Animation animation = AnimationUtils.loadAnimation(mContext, android.R.anim.slide_in_left);
            viewToAnimate.startAnimation(animation);
            lastPosition = position;
        }
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public final View mView;
        public final TextView mIdView;
        public final ImageView mImgView;
        public final TextView mContentView;
        public Product mItem;

        public ViewHolder(View view) {
            super(view);
            mView = view;
            mIdView = (TextView) view.findViewById(R.id.product_quantity_title);
            mContentView = (TextView) view.findViewById(R.id.product_quantity_title);
            mImgView = (ImageView) view.findViewById(R.id.product_quantity_image);

            mView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (null != mListener) {
                        mListener.onClick(v);
                    }
                }
            });
        }

        @Override
        public String toString() {
            return super.toString() + " '" + mContentView.getText() + "'";
        }
    }
}

我知道它必须在 onBindViewHolder 中，因为它被要求更新每个视图，但我没有正确更新 ImageView。

它与库无关。在不缓存图像的情况下进行延迟加载时也会发生相同的行为。错误是因为我不知道如何更新onBindViewHolder中的ImageView。

谢谢！

Answer 1

您需要确保只在 App 中初始化一次 ImageLoader。 创建一个类并使用 Application 扩展它，然后放入 AndroidManifest.xml 中，如下所示：

<application
        android:name=".App"
.../>

应用类

public class App extends Application {

    @Override
    public void onCreate() {
        super.onCreate();

        // UNIVERSAL IMAGE LOADER SETUP
        DisplayImageOptions defaultOptions = new DisplayImageOptions.Builder()
                .resetViewBeforeLoading(true)
                .cacheOnDisk(true)
                .cacheInMemory(true)
                .imageScaleType(ImageScaleType.EXACTLY)
                .displayer(new FadeInBitmapDisplayer(300))
                .build();

        ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(getApplicationContext())
                .defaultDisplayImageOptions(defaultOptions)
                .memoryCache(new WeakMemoryCache())
                .diskCacheSize(100 * 1024 * 1024)
                .build();

        ImageLoader.getInstance().init(config);
        // END - UNIVERSAL IMAGE LOADER SETUP
    }
}

对于你想知道的onBindViewHolder：

@Override
public void onBindViewHolder(final CategoryHolder holder, final int i) {

    holder.categoryImage.setImageBitmap(null);

    if (mRow.get(i).getImage() != null && !mRow.get(i).getImage().equals("")) {
        final File image = DiskCacheUtils.findInCache(mRow.get(i).getImage(), imageLoader.getDiskCache());
        if (image!= null && image.exists()) {
            Picasso.with(getActivity()).load(image).fit().centerCrop().into(holder.categoryImage);
        } else {
            imageLoader.loadImage(mRow.get(i).getImage(), new ImageLoadingListener() {
                @Override
                public void onLoadingStarted(String s, View view) {
                    holder.categoryImage.setImageBitmap(null);
                }

                @Override
                public void onLoadingFailed(String s, View view, FailReason failReason) {

                }

                @Override
                public void onLoadingComplete(String s, View view, final Bitmap bitmap) {
                    Picasso.with(getActivity()).load(s).fit().centerCrop().into(holder.categoryImage);

                }

                @Override
                public void onLoadingCancelled(String s, View view) {

                }
            });
        }
    }else {
        holder.categoryImage.setImageBitmap(null);
    }

    holder.categoryName.setText(mRow.get(i).getName().toUpperCase());

}

Answer 2

我认为错误是由于图像加载器的多个实例造成的：

ImageLoader imageLoader = ImageLoader.getInstance(); 

尝试为适配器创建一个相同的实例。用其他类变量声明它。您通过在onBindViewHolder() 中调用它来创建图像加载器的多个实例。