在 Picasso 图像加载器中加载位图图像会减慢列表视图中的滚动速度

Posted 2023-05-07

【中文标题】在 Picasso 图像加载器中加载位图图像会减慢列表视图中的滚动速度

【英文标题】：Loading bitmap images in Picasso Image loader slows down scrolling in a listview

【发布时间】：2015-09-21 23:42:16

【问题描述】：

我正在尝试生成在 sdcard 文件夹中找到的所有视频的缩略图，并使用 Picasso Image loader 在列表视图中填充所有生成的位图。一切正常，但速度非常慢，我无法滚动列表视图，它的滞后非常缓慢。我在该列表视图中有大约 150 个视图。有什么帮助吗？？ .谢谢提前。

public class VideoFilesAdapter extends ArrayAdapter<String> 
    private List<String> mpath;
    private Context mContext;
    public static ArrayList<String> mSelectedPaths = null;

    public VideoFilesAdapter(Context context, List<String> path) 
        super(context, R.layout.fileadapter_list, path);
        this.mContext = context;
        this.mpath = path;
    

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) 
        if (convertView == null) 
            LayoutInflater mInflater = (LayoutInflater) mContext
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = mInflater.inflate(R.layout.fileadapter_list, null);
        
        TextView txtTitle = (TextView) convertView.findViewById(R.id.txt);
        ImageView imageView = (ImageView) convertView.findViewById(R.id.img);

        File file = new File(mpath.get(position));

        if (file.exists()) 

            txtTitle.setText(file.getName());

            Bitmap bitmap = ThumbnailUtils.createVideoThumbnail(
                    file.getAbsolutePath(),
                    MediaStore.Video.Thumbnails.MICRO_KIND);

            Picasso.with(mContext).load(getImageUri(mContext, bitmap))
                    .centerInside().resize(100, 100)
                    .placeholder(R.drawable.holder).error(R.drawable.error)
                    .into(imageView);

        

        return convertView;
    

    public Uri getImageUri(Context inContext, Bitmap inImage) 
        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
        inImage.compress(Bitmap.CompressFormat.JPEG, 20, bytes);
        String path = Images.Media.insertImage(inContext.getContentResolver(),
                inImage, "Title", null);
        return Uri.parse(path);
    

【问题讨论】：

你的代码的问题是你的 Inflating TextView 和 ImageView 每次单元格视图被回收，基本上它会减慢你的滚动体验。

那么解决办法是什么？？ @龙

我现在正在编码，我可能会在明天之前发送给您 :) 我会尽可能解释每个部分。

【参考方案1】：

更新 看起来您并没有以任何方式存储/缓存这些位图，所以它一遍又一遍地做。试试这里找到的解决方案：Video thumbnail arrayadopter is slow on scroll

---

我不认为毕加索会减慢您ListView 的滚动速度。您的列表项有多复杂？如果它们嵌套了许多视图，可能就是这样，我在 ListView 中有超过 700 个项目，没有性能问题。

【讨论】：

我知道速度变慢是因为ThumbnailUtils.createVideoThumbnail 函数会生成文件夹中所有视频文件的缩略图。有什么办法可以解决吗？

【参考方案2】：

当我查看代码时，我看到 TextView 和 ImageView 每次调用 getView 时都会被夸大。通货膨胀是一项非常昂贵的任务，因此我们希望尽可能避免使用它。

在其他任何事情之前，请确保您将在 Gradle 中声明它

compile 'com.android.support:support-v4:21.0.0'

在你的 VideoFilesAdapter.java 中添加这个帮助类

 class Helper 
        public TextView textView;
        public ImageView image;
  

然后我们将使用 LRUcache 来存储图像，这样我们就可以一遍又一遍地使用这个图像而无需做太多的工作。

在你的项目中添加MyLRU.java

import android.content.Context;
import android.graphics.Bitmap;
import android.support.v4.util.LruCache;

public class MyLRU 

    private LruCache<String, Bitmap> cache = null;
    private static MyLRU myLru = null;

    private MyLRU() 
        int availableMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
        cache = new LruCache<String, Bitmap>(availableMemory / 8) 
            @Override
            protected int sizeOf(String key, Bitmap value) 
                // this is the only way to get the Bitmap size below API 12
                return (value.getRowBytes() * value.getHeight()) / 1024;
            
        ;
    

    public static MyLRU getInstance() 
        if (myLru == null) 
            myLru = new MyLRU();
        
        return myLru;
    

    public void addImage(String key, Bitmap image) 
        myLru.addImage(key, image);
    

    public Bitmap getImage(String key) 
        return myLru.getImage(key);
    

在你的VideoFilesAdapter.java中添加一个实用方法

public static Bitmap scaleCenterCrop(Bitmap source, int newHeight, int newWidth) 
        int sourceWidth = source.getWidth();
        int sourceHeight = source.getHeight();

        // Compute the scaling factors to fit the new height and width, respectively.
        // To cover the final image, the final scaling will be the bigger
        // of these two.
        float xScale = (float) newWidth / sourceWidth;
        float yScale = (float) newHeight / sourceHeight;
        float scale = Math.max(xScale, yScale);

        // Now get the size of the source bitmap when scaled
        float scaledWidth = scale * sourceWidth;
        float scaledHeight = scale * sourceHeight;

        // Let's find out the upper left coordinates if the scaled bitmap
        // should be centered in the new size give by the parameters
        float left = (newWidth - scaledWidth) / 2;
        float top = (newHeight - scaledHeight) / 2;

        // The target rectangle for the new, scaled version of the source bitmap will now
        // be
        RectF targetRect = new RectF(left, top, left + scaledWidth, top + scaledHeight);

        // Finally, we create a new bitmap of the specified size and draw our new,
        // scaled bitmap onto it.
        Bitmap dest = Bitmap.createBitmap(newWidth, newHeight, source.getConfig());
        Canvas canvas = new Canvas(dest);
        canvas.drawBitmap(source, null, targetRect, null);

        return dest;
    

这是您的VideoFilesAdapter.java的完整修改

public class VideoFilesAdapter extends ArrayAdapter<String> 
    private List<String> mpath;
    private Context mContext;
    public static ArrayList<String> mSelectedPaths = null;
    private MyLRU lruCache;

    public VideoFilesAdapter(Context context, List<String> path) 
        super(context, R.layout.fileadapter_list, path);
        this.mContext = context;
        this.mpath = path;
        // My LRU
        lruCache = MyLRU.getInstance();
    

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) 
        View v;
        if (convertView == null) 
            LayoutInflater mInflater = (LayoutInflater) mContext
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = mInflater.inflate(R.layout.fileadapter_list, null);
            Helper h = new Helper();
            h.textView = (TextView) convertView.findViewById(R.id.txt);
            h.textView = (ImageView) convertView.findViewById(R.id.img);
            v.setTag(h);
         else 
            v = convertView;
        

        Helper myHelper = (Helper) v.getTag();

        File file = new File(mpath.get(position));
        String fullPath = file.getAbsolutePath();

        if (file.exists()) 
            myHelper.textView.setText(file.getName());

            Bitmap cacheImage = lruCache.getImage(fullPath);
            if (cacheImage == null) 
                Bitmap bm = scaleCenterCrop(ThumbnailUtils.createVideoThumbnail(fullPath, MediaStore.Video.Thumbnails.MICRO_KIND),100,100);
                lruCache.addImage(fullPath, bm);
                cacheImage = bm;
            
            myHelper.image.setImageBitmap(cacheImage);

        

        return v;
    

    class Helper 
        public TextView textView;
        public ImageView image;
    

    public static Bitmap scaleCenterCrop(Bitmap source, int newHeight, int newWidth) 
        int sourceWidth = source.getWidth();
        int sourceHeight = source.getHeight();

        // Compute the scaling factors to fit the new height and width, respectively.
        // To cover the final image, the final scaling will be the bigger
        // of these two.
        float xScale = (float) newWidth / sourceWidth;
        float yScale = (float) newHeight / sourceHeight;
        float scale = Math.max(xScale, yScale);

        // Now get the size of the source bitmap when scaled
        float scaledWidth = scale * sourceWidth;
        float scaledHeight = scale * sourceHeight;

        // Let's find out the upper left coordinates if the scaled bitmap
        // should be centered in the new size give by the parameters
        float left = (newWidth - scaledWidth) / 2;
        float top = (newHeight - scaledHeight) / 2;

        // The target rectangle for the new, scaled version of the source bitmap will now
        // be
        RectF targetRect = new RectF(left, top, left + scaledWidth, top + scaledHeight);

        // Finally, we create a new bitmap of the specified size and draw our new,
        // scaled bitmap onto it.
        Bitmap dest = Bitmap.createBitmap(newWidth, newHeight, source.getConfig());
        Canvas canvas = new Canvas(dest);
        canvas.drawBitmap(source, null, targetRect, null);

        return dest;
    

如您所见，我暂时删除了 getImageUri 方法和 Picasso，因为它已经没有意义了，因为我们已经有一个缓存，即 LRU-cache。

我希望这会提高您的应用性能:)

【讨论】：

07-05 23:14:17.282: E/AndroidRuntime(4681): java.lang.***Error: 堆栈大小 8MB 07-05 23:14:17.282: E/AndroidRuntime(4681): 在com.example.myapp.helper.MyLRU.getImage(MyLRU.java:34)

我认为问题是您的设备内存不足，请尝试将 availableMemory / 8 更改为 availableMemory / 4 并告诉我会发生什么发生。