Question

我的listview工作得非常好。当我快速向上或向下滚动时，它每次显示相同的3-4张图片，然后慢慢变成右图像。

检索我认为需要修复的位图的代码

public Bitmap retrieveBitmap(String url) throws Exception {
        InputStream inputStream = null;
        try {
            inputStream = this.retrieveStream(url);
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inSampleSize = 8;
            final Bitmap bitmap = BitmapFactory.decodeStream(inputStream, null, options);
            return bitmap;
        } finally {
            try {
                if (inputStream != null) {
                    inputStream.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

在我添加选项样本大小之前，它一直在我滚动时崩溃，我只是将其复制到另一个堆栈问题但不确定它究竟是做什么，除了以某种方式减小大小。

适配器类

package com.example.jdmb;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MoviesAdapter extends ArrayAdapter<Movies> {
    private ArrayList<Movies> movieData;
    private Activity context;

    public MoviesAdapter(Context context, int resource,
            ArrayList<Movies> objects) {
        super(context, resource, objects);
        this.context = (Activity) context;
        this.movieData = objects;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = convertView;
        ViewHolder holder;
        if (view == null) {
            LayoutInflater vi = (LayoutInflater) context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            view = vi.inflate(R.layout.list_row, parent, false);
            holder = new ViewHolder();
            holder.id = (TextView) view.findViewById(R.id.movieId);
            holder.title = (TextView) view.findViewById(R.id.movieTitle);
            holder.vote_avg = (TextView) view.findViewById(R.id.movieAvg);
            holder.backdrop_path = (ImageView) view
                    .findViewById(R.id.movieBackdrop);
            holder.release_date = (TextView) view
                    .findViewById(R.id.movieRelease);
            holder.original_title = (TextView) view
                    .findViewById(R.id.movieTitle2);
            holder.vote_count = (TextView) view.findViewById(R.id.movieCount);
            holder.adult = (TextView) view.findViewById(R.id.movieAdult);
            holder.poster = (ImageView) view.findViewById(R.id.moviePoster);
            holder.popularity = (TextView) view
                    .findViewById(R.id.moviePopularity);
            view.setTag(holder);

        } else {
            holder = (ViewHolder) view.getTag();

        }
        Movies movie = movieData.get(position);

        if (movie != null) {
            // check to see if each individual textview is null.
            // if not, assign some text!

            holder.id.setText("id: " + movie.getId());
            holder.title.setText("title: " + movie.getTitle());
            holder.vote_avg.setText("vote_avg: " + movie.getVote_average());
            DownloadBitmap.downloadBitmap(holder.backdrop_path,
                    movie.getBackdrop_path());
            holder.release_date.setText("release_date: "
                    + movie.getRelease_date());
            holder.original_title.setText("original_title: "
                    + movie.getOriginal_title());
            holder.vote_count.setText("vote_count: " + movie.getVote_count());
            holder.adult.setText("adult: " + movie.isAdult());
            DownloadBitmap
                    .downloadBitmap(holder.poster, movie.getPoster_path());
            holder.popularity.setText("popularity: " + movie.getPopularity());

        }
        return view;

    }

    private static class ViewHolder {
        TextView id;
        TextView title;
        TextView vote_avg;
        ImageView backdrop_path;
        TextView release_date;
        TextView original_title;
        TextView vote_count;
        TextView adult;
        ImageView poster;
        TextView popularity;
    }
}

下载课程

package com.example.jdmb;

import java.io.InputStream;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.os.AsyncTask;
import android.widget.ImageView;

public class DownloadBitmap {
    static Bitmap image;

    public static void downloadBitmap(final ImageView imageView,
            final String url) {

        new AsyncTask<Bitmap, Void, Bitmap>() {

            @Override
            protected Bitmap doInBackground(Bitmap... params) {
                HttpRetriever retriever = new HttpRetriever();
                try {                   
                    image = retriever.retrieveBitmap(url);
                } catch (Exception e) {
                }
                return image;

            }

            @Override
            protected void onPostExecute(Bitmap result) {
                super.onPostExecute(result);
                if (imageView != null) {

                    imageView.setImageBitmap(result);
                }
            }

        }.execute();

    }
}

我的代码的哪一部分让我在滚动时看到相同的照片，我认为它与回收图像有关，但不知道如何通过它。

Answer 1

回收的ImageView会显示您告诉它的最后一个位图。您需要设置holder.backdrop_path＆amp;在返回视图之前或在AsyncTask的onPreExecute之前将holder.poster发送到通用资源。

像这样：

package com.example.jdmb;

import java.io.InputStream;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.widget.ImageView;

public class DownloadBitmap {
    static Bitmap image;

    public static void downloadBitmap(final ImageView imageView,
            final String url) {

        new AsyncTask<Bitmap, Void, Bitmap>() {

            protected void onPreExecute(){
                //This could also be an internal resource instead of null
                imageView.setImageBitmap(null);
            }

            @Override
            protected Bitmap doInBackground(Bitmap... params) {
                HttpRetriever retriever = new HttpRetriever();
                InputStream is = retriever.retrieveStream(url);
                image = BitmapFactory.decodeStream(is);
                return image;

            }

            @Override
            protected void onPostExecute(Bitmap result) {
                super.onPostExecute(result);
                imageView.setImageBitmap(result);

            }

        }.execute();

    }
}

我会建议一种更强大的方法来完成这项任务。此解决方案将要求您使用Volley Library，并且大多数代码都可以在Google IO source中找到。如果有帮助的话，Here是一个涵盖相同主题的视频。

下载Volley并将其添加到您的构建路径中。我们将使用Volley ImageLoader的Google IO超类。

*
 * Copyright 2012 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.android.apps.iosched.util;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.TransitionDrawable;
import android.net.http.AndroidHttpClient;
import android.os.Build;
import android.os.Environment;
import android.support.v4.app.FragmentActivity;
import android.widget.ImageView;

import com.android.volley.Cache;
import com.android.volley.Network;
import com.android.volley.RequestQueue;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.BasicNetwork;
import com.android.volley.toolbox.DiskBasedCache;
import com.android.volley.toolbox.HttpClientStack;
import com.android.volley.toolbox.HurlStack;

import java.io.File;
import java.util.ArrayList;

/**
 * A class that wraps up remote image loading requests using the Volley library combined with a
 * memory cache. An single instance of this class should be created once when your Activity or
 * Fragment is created, then use {@link #get(String, android.widget.ImageView)} or one of
 * the variations to queue the image to be fetched and loaded from the network. Loading images
 * in a {@link android.widget.ListView} or {@link android.widget.GridView} is also supported but
 * you must store the {@link com.android.volley.Request} in your ViewHolder type class and pass it
 * into loadImage to ensure the request is canceled as views are recycled.
 */
public class ImageLoader extends com.android.volley.toolbox.ImageLoader {
    private static final ColorDrawable transparentDrawable = new ColorDrawable(
            android.R.color.transparent);
    private static final int HALF_FADE_IN_TIME = UIUtils.ANIMATION_FADE_IN_TIME / 2;
    private static final String CACHE_DIR = "images";

    private Resources mResources;
    private ArrayList<Drawable> mPlaceHolderDrawables;
    private boolean mFadeInImage = true;
    private int mMaxImageHeight = 0;
    private int mMaxImageWidth = 0;

    /**
     * Creates an ImageLoader with Bitmap memory cache. No default placeholder image will be shown
     * while the image is being fetched and loaded.
     */
    public ImageLoader(FragmentActivity activity) {
        super(newRequestQueue(activity),
                BitmapCache.getInstance(activity.getSupportFragmentManager()));
        mResources = activity.getResources();
    }

    /**
     * Creates an ImageLoader with Bitmap memory cache and a default placeholder image while the
     * image is being fetched and loaded.
     */
    public ImageLoader(FragmentActivity activity, int defaultPlaceHolderResId) {
        super(newRequestQueue(activity),
                BitmapCache.getInstance(activity.getSupportFragmentManager()));
        mResources = activity.getResources();
        mPlaceHolderDrawables = new ArrayList<Drawable>(1);
        mPlaceHolderDrawables.add(defaultPlaceHolderResId == -1 ?
                null : mResources.getDrawable(defaultPlaceHolderResId));
    }

    /**
     * Creates an ImageLoader with Bitmap memory cache and a list of default placeholder drawables.
     */
    public ImageLoader(FragmentActivity activity, ArrayList<Drawable> placeHolderDrawables) {
        super(newRequestQueue(activity),
                BitmapCache.getInstance(activity.getSupportFragmentManager()));
        mResources = activity.getResources();
        mPlaceHolderDrawables = placeHolderDrawables;
    }

    /**
     * Starts processing requests on the {@link RequestQueue}.
     */
    public void startProcessingQueue() {
        getRequestQueue().start();
    }

    /**
     * Stops processing requests on the {@link RequestQueue}.
     */
    public void stopProcessingQueue() {
        getRequestQueue().stop();
    }

    public ImageLoader setFadeInImage(boolean fadeInImage) {
        mFadeInImage = fadeInImage;
        return this;
    }

    public ImageLoader setMaxImageSize(int maxImageWidth, int maxImageHeight) {
        mMaxImageWidth = maxImageWidth;
        mMaxImageHeight = maxImageHeight;
        return this;
    }

    public ImageLoader setMaxImageSize(int maxImageSize) {
        return setMaxImageSize(maxImageSize, maxImageSize);
    }

    public ImageContainer get(String requestUrl, ImageView imageView) {
        return get(requestUrl, imageView, 0);
    }

    public ImageContainer get(String requestUrl, ImageView imageView, int placeHolderIndex) {
        return get(requestUrl, imageView, mPlaceHolderDrawables.get(placeHolderIndex),
                mMaxImageWidth, mMaxImageHeight);
    }

    public ImageContainer get(String requestUrl, ImageView imageView, Drawable placeHolder) {
        return get(requestUrl, imageView, placeHolder, mMaxImageWidth, mMaxImageHeight);
    }

    public ImageContainer get(String requestUrl, ImageView imageView, Drawable placeHolder,
            int maxWidth, int maxHeight) {

        // Find any old image load request pending on this ImageView (in case this view was
        // recycled)
        ImageContainer imageContainer = imageView.getTag() != null &&
                imageView.getTag() instanceof ImageContainer ?
                (ImageContainer) imageView.getTag() : null;

        // Find image url from prior request
        String recycledImageUrl = imageContainer != null ? imageContainer.getRequestUrl() : null;

        // If the new requestUrl is null or the new requestUrl is different to the previous
        // recycled requestUrl
        if (requestUrl == null || !requestUrl.equals(recycledImageUrl)) {
            if (imageContainer != null) {
                // Cancel previous image request
                imageContainer.cancelRequest();
                imageView.setTag(null);
            }
            if (requestUrl != null) {
                // Queue new request to fetch image
                imageContainer = get(requestUrl,
                        getImageListener(mResources, imageView, placeHolder, mFadeInImage),
                        maxWidth, maxHeight);
                // Store request in ImageView tag
                imageView.setTag(imageContainer);
            } else {
                imageView.setImageDrawable(placeHolder);
                imageView.setTag(null);
            }
        }

        return imageContainer;
    }

    private static ImageListener getImageListener(final Resources resources,
            final ImageView imageView, final Drawable placeHolder, final boolean fadeInImage) {
        return new ImageListener() {
            @Override
            public void onResponse(ImageContainer response, boolean isImmediate) {
                imageView.setTag(null);
                if (response.getBitmap() != null) {
                    setImageBitmap(imageView, response.getBitmap(), resources,
                            fadeInImage && !isImmediate);
                } else {
                    imageView.setImageDrawable(placeHolder);
                }
            }

            @Override
            public void onErrorResponse(VolleyError volleyError) {
            }
        };
    }

    private static RequestQueue newRequestQueue(Context context) {

        // On HC+ use HurlStack which is based on HttpURLConnection. Otherwise fall back on
        // AndroidHttpClient (based on Apache DefaultHttpClient) which should no longer be used
        // on newer platform versions where HttpURLConnection is simply better.
        Network network = new BasicNetwork(
                UIUtils.hasHoneycomb() ?
                        new HurlStack() :
                        new HttpClientStack(AndroidHttpClient.newInstance(
                                NetUtils.getUserAgent(context))));

        Cache cache = new DiskBasedCache(getDiskCacheDir(context, CACHE_DIR));
        RequestQueue queue = new RequestQueue(cache, network);
        queue.start();
        return queue;
    }

    /**
     * Sets a {@link android.graphics.Bitmap} to an {@link android.widget.ImageView} using a
     * fade-in animation. If there is a {@link android.graphics.drawable.Drawable} already set on
     * the ImageView then use that as the image to fade from. Otherwise fade in from a transparent
     * Drawable.
     */
    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1)
    private static void setImageBitmap(final ImageView imageView, final Bitmap bitmap,
            Resources resources, boolean fadeIn) {

        // If we're fading in and on HC MR1+
        if (fadeIn && UIUtils.hasHoneycombMR1()) {
            // Use ViewPropertyAnimator to run a simple fade in + fade out animation to update the
            // ImageView
            imageView.animate()
                    .scaleY(0.95f)
                    .scaleX(0.95f)
                    .alpha(0f)
                    .setDuration(imageView.getDrawable() == null ? 0 : HALF_FADE_IN_TIME)
                    .setListener(new AnimatorListenerAdapter() {
                        @Override
                        public void onAnimationEnd(Animator animation) {
                            imageView.setImageBitmap(bitmap);
                            imageView.animate()
                                    .alpha(1f)
                                    .scaleY(1f)
                                    .scaleX(1f)
                                    .setDuration(HALF_FADE_IN_TIME)
                                    .setListener(null);
                        }
                    });
        } else if (fadeIn) {
            // Otherwise use a TransitionDrawable to fade in
            Drawable initialDrawable;
            if (imageView.getDrawable() != null) {
                initialDrawable = imageView.getDrawable();
            } else {
                initialDrawable = transparentDrawable;
            }
            BitmapDrawable bitmapDrawable = new BitmapDrawable(resources, bitmap);
            // Use TransitionDrawable to fade in
            final TransitionDrawable td =
                    new TransitionDrawable(new Drawable[] {
                            initialDrawable,
                            bitmapDrawable
                    });
            imageView.setImageDrawable(td);
            td.startTransition(UIUtils.ANIMATION_FADE_IN_TIME);
        } else {
            // No fade in, just set bitmap directly
            imageView.setImageBitmap(bitmap);
        }
    }

    /**
     * Get a usable cache directory (external if available, internal otherwise).
     *
     * @param context The context to use
     * @param uniqueName A unique directory name to append to the cache dir
     * @return The cache dir
     */
    public static File getDiskCacheDir(Context context, String uniqueName) {
        // Check if media is mounted or storage is built-in, if so, try and use external cache dir
        // otherwise use internal cache dir

        // TODO: getCacheDir() should be moved to a background thread as it attempts to create the
        // directory if it does not exist (no disk access should happen on the main/UI thread).
        final String cachePath =
                Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
                        !Environment.isExternalStorageRemovable()
                        ? getExternalCacheDir(context).getPath()
                        : context.getCacheDir().getPath();

        return new File(cachePath + File.separator + uniqueName);
    }

    /**
     * Get the external app cache directory.
     *
     * @param context The context to use
     * @return The external cache dir
     */
    private static File getExternalCacheDir(Context context) {
        // TODO: This needs to be moved to a background thread to ensure no disk access on the
        // main/UI thread as unfortunately getExternalCacheDir() calls mkdirs() for us (even
        // though the Volley library will later try and call mkdirs() as well from a background
        // thread).
        return context.getExternalCacheDir();
    }

    /**
     * Interface an activity can implement to provide an ImageLoader to its children fragments.
     */
    public interface ImageLoaderProvider {
        public ImageLoader getImageLoaderInstance();
    }

}

现在在您的活动中创建ImageLoader并在创建适配器时将其传递给适配器。

@Override
public void onCreate(Bundle savedInstanceState){
...
ImageLoader mImageLoader = new ImageLoader(this, R.drawable.default_image);
MoviesAdapter  mMoviesAdapter = new MoviesAdapter(this, R.layout.your_list_layout, moviesList, mImageLoader);
...
}

调整Movie Adapter构造函数。

package com.example.jdmb;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MoviesAdapter extends ArrayAdapter<Movies> {
    private ArrayList<Movies> movieData;
    private Activity context;
    private ImageLoader mImageLoader;

    public MoviesAdapter(Context context, int resource,
            ArrayList<Movies> objects, ImageLoader loader) {
        super(context, resource, objects);
        this.context = (Activity) context;
        this.movieData = objects;
        this.mImageLoader = loader;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = convertView;
        ViewHolder holder;
        if (view == null) {
            LayoutInflater vi = (LayoutInflater) context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            view = vi.inflate(R.layout.list_row, parent, false);
            holder = new ViewHolder();
            holder.id = (TextView) view.findViewById(R.id.movieId);
            holder.title = (TextView) view.findViewById(R.id.movieTitle);
            holder.vote_avg = (TextView) view.findViewById(R.id.movieAvg);
            holder.backdrop_path = (ImageView) view
                    .findViewById(R.id.movieBackdrop);
            holder.release_date = (TextView) view
                    .findViewById(R.id.movieRelease);
            holder.original_title = (TextView) view
                    .findViewById(R.id.movieTitle2);
            holder.vote_count = (TextView) view.findViewById(R.id.movieCount);
            holder.adult = (TextView) view.findViewById(R.id.movieAdult);
            holder.poster = (ImageView) view.findViewById(R.id.moviePoster);
            holder.popularity = (TextView) view
                    .findViewById(R.id.moviePopularity);
            view.setTag(holder);

        } else {
            holder = (ViewHolder) view.getTag();

        }
        Movies movie = movieData.get(position);

        if (movie != null) {
            // check to see if each individual textview is null.
            // if not, assign some text!

            holder.id.setText("id: " + movie.getId());
            holder.title.setText("title: " + movie.getTitle());
            holder.vote_avg.setText("vote_avg: " + movie.getVote_average());
            mImageLoader.get(movie.getBackdrop_path(), holder.backdrop_path);
            holder.release_date.setText("release_date: "
                    + movie.getRelease_date());
            holder.original_title.setText("original_title: "
                    + movie.getOriginal_title());
            holder.vote_count.setText("vote_count: " + movie.getVote_count());
            holder.adult.setText("adult: " + movie.isAdult());
            mImageLoader.get(movie.getPoster_path(), holder.poster);
            holder.popularity.setText("popularity: " + movie.getPopularity());
        }
        return view;
    }

    private static class ViewHolder {
        TextView id;
        TextView title;
        TextView vote_avg;
        ImageView backdrop_path;
        TextView release_date;
        TextView original_title;
        TextView vote_count;
        TextView adult;
        ImageView poster;
        TextView popularity;
    }
}

我可能错过了某些内容或输入错误，因为我没有直接测试这个，但我在自己的应用程序中使用了类似的实现。

自定义arrayadapter仅在快速滚动时显示重复项

1 个答案: