Question

我有一个可以容纳图像的ListView。这取决于SDCARD中是否存在图像。

这是我的示例代码：

public class MainActivity extends Activity  {

    ListView mListView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mListView = new ListView(this);
        setContentView(mListView);

        String[] arr = new String[] { 
                "/example/images/1.jpg", "/example/images/2.jpg",  
                "/example/images/3.jpg", "/example/images/4.jpg",  
                "/example/images/5.jpg", "/example/images/6.jpg", 
                "/example/images/7.jpg", "/example/images/8.jpg",  
                "/example/images/9.jpg", "/example/images/1.jpg", 
                "/example/images/2.jpg", "/example/images/3.jpg",  
                "/example/images/4.jpg", "/example/images/5.jpg",  
                "/example/images/6.jpg", "/example/images/7.jpg",  
                "/example/images/8.jpg", "/example/images/9.jpg", 
                "/example/images/1.jpg", "/example/images/2.jpg",  
                "/example/images/3.jpg", "/example/images/4.jpg",  
                "/example/images/5.jpg", "/example/images/6.jpg", 
                "/example/images/7.jpg", "/example/images/8.jpg",  
                "/example/images/9.jpg", "/example/images/1.jpg", 
                "/example/images/2.jpg", "/example/images/3.jpg",  
                "/example/images/4.jpg", "/example/images/5.jpg",  
                "/example/images/6.jpg", "/example/images/7.jpg",  
                "/example/images/8.jpg", "/example/images/9.jpg"}; 

        List<String> list = Arrays.asList(arr);

        MyAdapter adapter = new MyAdapter(this, R.layout.listitem_imv, list);

        mListView.setAdapter(adapter);
    }

    class MyAdapter extends ArrayAdapter<String>{

        List<String> mList;
        LayoutInflater mInflater;
        int mResource;

        public MyAdapter(Context context, int resource,
                List<String> objects) {
            super(context, resource, objects);

            mResource = resource;
            mInflater = getLayoutInflater();
            mList = objects;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View view;

            if(convertView == null){
                view = mInflater.inflate(mResource, null);
            }else{
                view = convertView;
            }

            ImageView imageView = (ImageView) view.findViewById(R.id.imv);
            TextView textView = (TextView) view.findViewById(R.id.txv);

                            imageView.setTag(mList.get(position));//tag of imageView == path to image
            new LoadImage().execute(imageView);
            textView.setText(mList.get(position).toString());

            return view;
        }       
    }

    class LoadImage extends AsyncTask<Object, Void, Bitmap>{

        private ImageView imv;
        private String path;


        @Override
        protected Bitmap doInBackground(Object... params) {
            imv = (ImageView)   params[0];

            path = imv.getTag().toString();

            Bitmap bitmap = null;
            File file = new File( 
                    Environment.getExternalStorageDirectory().getAbsolutePath() + path);

            if(file.exists()){
                bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());
            }

            return bitmap;
        }
        @Override
        protected void onPostExecute(Bitmap result) {
            if(result != null && imv != null){
                imv.setVisibility(View.VISIBLE);
                imv.setImageBitmap(result);
            }else{
                imv.setVisibility(View.GONE);
            }
        }
    }
}

'sdcard / example / images'目录包含图像：1.jpg，2.jpg，3.jpg，4.jpg，6.jpg，7.jpg和9.jpg。预期的结果是： example

但是，如果我快速滚动列表，则会在错误的项目中插入一些图像。它是由于在getView（）方法中使用convertView而发生的。

如果我使用以下代码，代码可以正常工作：

        //if(convertView == null){
        //  view = mInflater.inflate(mResource, null);
        //}else{
        //  view = convertView;
        //}
        view = mInflater.inflate(mResource, null);

当列表快速滚动时，由于使用了convertView，两个asyncTasks可以引用同一个View。当视图不再可见时，如何取消AsyncTask？（并且由ListView的另一项使用）

修改

            @Override
    protected void onPostExecute(Bitmap result) {
        if(result != null && imv != null){

            if(imv.getTag().equals(path)){
                imv.setVisibility(View.VISIBLE);
                imv.setImageBitmap(result);
            }else{
                imv.setVisibility(View.GONE);
            }

        }else{
            imv.setVisibility(View.GONE);
        }
    }

Answer 1

您可以将ImageView发送到任务构造函数，并在那里保留对图像路径的引用。现在在onPostExecute中，检查ImageView的当前标记是否与您开始使用的标记相同。如果是，则设置图像。如果不是，请不要做任何事情。

但是，这意味着无论如何都会下载图像。你不会在视图上设置错误的图像。

修改首先将ImageView传递给任务构造函数：

new LoadImage(imageView).execute()

然后在LoadImage构造函数中保存对ImageView和图像路径的引用。在构造函数中而不是在doInBackground中保存路径非常重要，以确保我们不会遇到多线程问题。然后在onPostExecute我们检查当前路径。

class LoadImage extends AsyncTask<Object, Void, Bitmap>{ private ImageView imv; private String path; public LoadImage(ImageView imv) { this.imv = imv; this.path = imv.getTag().toString(); } @Override protected Bitmap doInBackground(Object... params) { Bitmap bitmap = null; File file = new File( Environment.getExternalStorageDirectory().getAbsolutePath() + path); if(file.exists()){ bitmap = BitmapFactory.decodeFile(file.getAbsolutePath()); } return bitmap; } @Override protected void onPostExecute(Bitmap result) { if (!imv.getTag().toString().equals(path)) { /* The path is not same. This means that this image view is handled by some other async task. We don't do anything and return. */ return; } if(result != null && imv != null){ imv.setVisibility(View.VISIBLE); imv.setImageBitmap(result); }else{ imv.setVisibility(View.GONE); } } }

Answer 2

这个Android Developers Blog post将为您提供完整的参考项目，包括缓存。只需用SD卡文件读取替换Http访问代码。

Answer 3

我希望这会有所帮助。经过大量的搜索，我有了这个有效的解决方案。

public class CustomAdapter extends ArrayAdapter<String>{
    /*
    public CustomAdapter(Context context , String[] video) {
        super(context,R.layout.custom_row, video);
    }
*/

private final Activity context;
private final String[] video;

static class ViewHolder {
    public TextView videoTitle;
    public ImageView videoThumbnail;
    public int position;
    public String path;
}

public CustomAdapter(Activity context, String[] video) {
    super(context, R.layout.custom_row, video);
    this.context = context;
    this.video = video;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {

    LayoutInflater videoInflator = LayoutInflater.from(getContext());
    View customView = videoInflator.inflate(R.layout.custom_row, parent, false);
        ViewHolder viewHolder = new ViewHolder();
        viewHolder.position = position;
        viewHolder.path = video[position];
        viewHolder.videoTitle = (TextView) customView.findViewById(R.id.videoTitle);
        viewHolder.videoThumbnail = (ImageView) customView.findViewById(R.id.videoThumbnail);
        //rowView.setTag(viewHolder);
    //}
    customView.setTag(viewHolder);


    final String videoItem = video[position];
    int index=videoItem.lastIndexOf('/');
    String lastString=(videoItem.substring(index +1));
    index = lastString.indexOf(".mp4");
    lastString=(lastString.substring(0,index));
    viewHolder.videoTitle.setText(lastString);

    new AsyncTask<ViewHolder, Void, Bitmap>() {
        private ViewHolder v;

        @Override
        protected Bitmap doInBackground(ViewHolder... params) {
            v = params[0];
            Bitmap thumb = ThumbnailUtils.createVideoThumbnail(videoItem, MediaStore.Images.Thumbnails.MINI_KIND);
            return thumb;
        }

        @Override
        protected void onPostExecute(Bitmap result) {
            super.onPostExecute(result);
            if (v.position == position) {
                // If this item hasn't been recycled already, hide the
                // progress and set and show the image
                v.videoThumbnail.setImageBitmap(result);
            }
        }
    }.execute(viewHolder);
    return customView;
}

}

Answer 4

也许你应该尝试：

view = mInflater.inflate(mResource,parent,null);

查看此博客，它解释了类似的问题：

http://www.doubleencore.com/2013/05/layout-inflation-as-intended/

Answer 5

我会做什么（除非你有数千张图片）： 1.创建一个数据结构 - 一个包含要显示的String名称和位图的简单类 2.为它创建一个适配器 3.在getView方法中将正确的位图分配给正确的ImageView。

在你的情况下，虽然你可以创建一个类似的数据结构，但不是一个位图而是一个AsyncTask。无论如何，您需要将asynctask与字符串绑定到一个项目中。这些项目的数组（或arraylist）将被送到您的适配器。显示的是图像视图和文本视图。

可以使用cancel（）取消AsyncTask。

Answer 6

嘿，我发现这个问题的解决方案只是使用以下函数而不是函数

 @Override
protected void onPostExecute(Bitmap result) {

    if (!imv.getTag().toString().equals(rec_id)) {
           return;
    }

    if(result != null && imv != null){
        int index = id.indexOf(imv.getTag().toString());
        if(list.getFirstVisiblePosition()<=index && index<=list.getLastVisiblePosition())
        {
            imv.setVisibility(View.VISIBLE);
            imv.setImageBitmap(result);
        }
    }else{
        imv.setImageBitmap(icon);
        imv.setVisibility(View.GONE);
    }
}

此处列表是listview的对象。只需将列表视图对象传递给适配器并粘贴此函数，而不是onPostExecute函数。

使用AsyncTask在ListView中加载图像

6 个答案: