我有一堆来自 sdcard 的图像，它们在 gridview 上异步加载。一切正常，但是当通过长按任何图像访问多选上下文操作菜单时，整个 Activity 会重新加载，所有图像都会重新加载。如何预防？

我的适配器

public class PhotosGridViewImageAdapter extends BaseAdapter {

AsyncTaskLoadFiles myAsyncTaskLoadFiles;

public class AsyncTaskLoadFiles extends AsyncTask<Void, String, Void> {

    File targetDirector;
    PhotosGridViewImageAdapter myTaskAdapter;

    public AsyncTaskLoadFiles(PhotosGridViewImageAdapter adapter) {
        myTaskAdapter = adapter;
    }

    @Override
    protected void onPreExecute() {
        String ExternalStorageDirectoryPath = Environment
                .getExternalStorageDirectory().getAbsolutePath();
        String targetPath = ExternalStorageDirectoryPath + File.separator + AppConstant.PHOTO_ALBUM + File.separator;
        targetDirector = new File(targetPath);
        myTaskAdapter.clear();

        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(Void... params) {
        File[] files = targetDirector.listFiles();
        Arrays.sort(files);
        for (File file : files) {
            publishProgress(file.getAbsolutePath());
            if (isCancelled()) break;
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(String... values) {
        myTaskAdapter.add(values[0]);
        super.onProgressUpdate(values);
    }

    @Override
    protected void onPostExecute(Void result) {
        myTaskAdapter.notifyDataSetChanged();
        super.onPostExecute(result);
    }

}

ArrayList<String> itemList = new ArrayList<String>();

void add(String path) {
    itemList.add(path);
}

void clear() {
    itemList.clear();
}

void remove(int index){
    itemList.remove(index);
}

private Activity _activity;
private ArrayList<String> _filePaths = new ArrayList<String>();
private int imageWidth;

public PhotosGridViewImageAdapter(Activity activity, ArrayList<String> filePaths,
        int imageWidth) {
    this._activity = activity;
    this._filePaths = filePaths;
    this.imageWidth = imageWidth;
}

@Override
public int getCount() {
    return this._filePaths.size();
}

@Override
public Object getItem(int position) {
    return this._filePaths.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    final ImageView imageView;
    if (convertView == null) {
        imageView = new ImageView(_activity);
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        imageView.setLayoutParams(new GridView.LayoutParams(imageWidth,
                imageWidth));

        convertView = imageView;

        holder = new ViewHolder();
        holder.image = imageView;
        holder.position = position;
        convertView.setTag(holder);
    } else {
        //imageView = (ImageView) convertView;
        holder = (ViewHolder) convertView.getTag();
        ((ImageView)convertView).setImageBitmap(null);
    }

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

        // get screen dimensions
        @Override
        protected Bitmap doInBackground(ViewHolder... params) {
            v = params[0];
            Bitmap image = decodeFile(_filePaths.get(position), imageWidth,
                    imageWidth);
            //imageView.setImageBitmap(image);
            return image;
        }
        @Override
        protected void onPostExecute(Bitmap result) {
            super.onPostExecute(result);
            v.image.setImageBitmap(result);

        }
    }.execute(holder);

    return convertView;
}

/*
 * Resizing image size
 */
public Bitmap decodeFile(String filePath, int WIDTH, int HEIGHT) {
    try {
        File f = new File(filePath);
        if(filePath.contains(".jpg")) {
            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(f), null, o);

            final int REQUIRED_WIDTH = WIDTH;
            final int REQUIRED_HEIGHT = HEIGHT;
            int scale = 1;
            while (o.outWidth / scale / 2 >= REQUIRED_WIDTH
                    && o.outHeight / scale / 2 >= REQUIRED_HEIGHT)
                scale *= 2;

            BitmapFactory.Options o2 = new BitmapFactory.Options();
            o2.inSampleSize = scale;
            return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
        }else  if(filePath.contains(".mp4")){
            return ThumbnailUtils.createVideoThumbnail(filePath, 0);
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    return null;
}
class ViewHolder {
    ImageView image;
    int position;
}
}

上下文操作菜单代码

public class MultiChoiceModeListener implements
        GridView.MultiChoiceModeListener {
    public boolean onCreateActionMode(ActionMode mode, Menu menu) {
        MenuInflater inflater = mode.getMenuInflater();
        inflater.inflate(R.menu.contextual_action_menu, menu);
        //mode.setTitle("Select Items");
        mode.setTitle("1 item selected");
        return true;
    }

    public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
        return true;
    }
    public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
        // Respond to clicks on the actions in the CAB
        switch (item.getItemId()) {
            case R.id.delete:
                SparseBooleanArray checked = gridView.getCheckedItemPositions();
                try {
                    int len = checked.size();
                    for (int i = 0; i < len; i++) {
                        if (checked.valueAt(i)) {
                            Integer position = checked.keyAt(i);
                            //deleteToMessageHistory(position);
                        }
                    }
                }catch (Exception i){
                    Toast.makeText(PhotosGridViewActivity.this, "Message was not deleted. Try again.", Toast.LENGTH_SHORT).show();
                }
                mode.finish(); // Action picked, so close the CAB
                return true;
            default:
                return false;
        }
    }
    public void onDestroyActionMode(ActionMode mode) {
    }
    public void onItemCheckedStateChanged(ActionMode mode, int position,
                                          long id, boolean checked) {
        int selectCount = gridView.getCheckedItemCount();
        switch (selectCount) {
            case 1:
                mode.setTitle("1 item selected");
                break;
            default:
                mode.setTitle("" + selectCount + " items selected");
                break;
        }
    }
}

感谢您的帮助!

==UPDATE==

这是 MainActivity 代码:

public class PhotosGridViewActivity extends Activity {

private PhotosUtils utils;
private ArrayList<String> imagePaths = new ArrayList<String>();
private PhotosGridViewImageAdapter adapter;
private GridView gridView;
private int columnWidth;

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

    // Initilizing Grid View
    InitilizeGridLayout();

}

private void InitilizeGridLayout() {
    setContentView(R.layout.photos_grid_view);
    utils = new PhotosUtils(PhotosGridViewActivity.this);
    gridView = (GridView) findViewById(R.id.grid_view);
    // loading all image paths from SD card
    imagePaths = utils.getFilePaths();
    Resources r = getResources();
    float padding = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
            AppConstant.GRID_PADDING, r.getDisplayMetrics());

    columnWidth = (int) ((utils.getScreenWidth() - ((AppConstant.NUM_OF_COLUMNS + 1) * padding)) / AppConstant.NUM_OF_COLUMNS);

    gridView.setNumColumns(AppConstant.NUM_OF_COLUMNS);
    gridView.setColumnWidth(columnWidth);
    gridView.setStretchMode(GridView.NO_STRETCH);
    gridView.setPadding((int) padding, (int) padding, (int) padding,
            (int) padding);
    gridView.setHorizontalSpacing((int) padding);
    gridView.setVerticalSpacing((int) padding);

    gridView.setChoiceMode(GridView.CHOICE_MODE_MULTIPLE_MODAL);
    gridView.setMultiChoiceModeListener(new MultiChoiceModeListener());

    // Gridview adapter
    adapter = new PhotosGridViewImageAdapter(PhotosGridViewActivity.this, imagePaths,
            columnWidth);
    // setting grid view adapter
    gridView.setAdapter(adapter);

    gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
            gridView.getItemAtPosition(position);
            Intent i = new Intent(PhotosGridViewActivity.this, PhotosScreenViewActivity.class);
            i.putExtra("position", position);
            PhotosGridViewActivity.this.startActivity(i);
        }
    });
}

public class MultiChoiceModeListener implements
        GridView.MultiChoiceModeListener {
    public boolean onCreateActionMode(ActionMode mode, Menu menu) {
        MenuInflater inflater = mode.getMenuInflater();
        inflater.inflate(R.menu.contextual_action_menu, menu);
        //mode.setTitle("Select Items");
        mode.setTitle("1 item selected");
        return true;
    }

    public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
        return true;
    }
    public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
        // Respond to clicks on the actions in the CAB
        switch (item.getItemId()) {
            case R.id.delete:
                SparseBooleanArray checked = gridView.getCheckedItemPositions();
                try {
                    int len = checked.size();
                    for (int i = 0; i < len; i++) {
                        if (checked.valueAt(i)) {
                            Integer position = checked.keyAt(i);
                            //deleteToMessageHistory(position);
                        }
                    }
                }catch (Exception i){
                    Toast.makeText(PhotosGridViewActivity.this, "Message was not deleted. Try again.", Toast.LENGTH_SHORT).show();
                }
                mode.finish(); // Action picked, so close the CAB
                return true;
            default:
                return false;
        }
    }
    public void onDestroyActionMode(ActionMode mode) {
    }
    public void onItemCheckedStateChanged(ActionMode mode, int position,
                                          long id, boolean checked) {
        int selectCount = gridView.getCheckedItemCount();
        switch (selectCount) {
            case 1:
                mode.setTitle("1 item selected");
                break;
            default:
                mode.setTitle("" + selectCount + " items selected");
                break;
        }
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(co.glurl.appoid.R.menu.photo_gallery, menu);
    return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.add:
            /** Go to the user's add photos. */
            startActivity(new Intent(this, PhotoIntentActivity.class));
            break;
        //case R.id.settings:
            /** Go to the user's settings photos. */
        //    startActivity(new Intent(this, PhotoGridSettings.class));
        //    break;
        default:
            return super.onContextItemSelected(item);
    }
    return true;
}

}

最佳答案

我的解决方案。感谢@pushbit 指导我完成它。

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    ImageView imageView = (ImageView) convertView;
    if (imageView == null) {
        imageView = new ImageView(_activity);
    }

    // Trigger the download of the URL asynchronously into the image view.
    if(_filePaths.get(position).contains(".jpg")) {
        Picasso.with(_activity)
                .load(new File(_filePaths.get(position)))
                .resize(imageWidth, imageWidth)
                .centerCrop()
                .tag(_activity)
                .into(imageView);
    }else  if(_filePaths.get(position).contains(".mp4")){
        VideoRequestHandler videoRequestHandler;
        Picasso picassoInstance;
        videoRequestHandler=new VideoRequestHandler();
        picassoInstance = new Picasso.Builder(_activity.getApplicationContext())
                .addRequestHandler(videoRequestHandler)
                .build();
        picassoInstance
                .load(videoRequestHandler.SCHEME_VIDEO+":"+_filePaths.get(position))
                .resize(imageWidth, imageWidth)
                .centerCrop()
                .tag(_activity)
                .into(imageView);
    }
    return imageView;
}

public static boolean deleteToPhotoAlbum(Integer position) {
    File file = new File(_filePaths.get(position));
    boolean deleted = file.delete();
    return deleted;
}

public class VideoRequestHandler extends RequestHandler {
    public String SCHEME_VIDEO  = "video";
    @Override
    public boolean canHandleRequest(Request data)
    {
        String scheme = data.uri.getScheme();
        return (SCHEME_VIDEO.equals(scheme));
    }

    @Override
    public Result load(Request data, int arg1) throws IOException
    {
        Bitmap bm = ThumbnailUtils.createVideoThumbnail(data.uri.getPath(), MediaStore.Images.Thumbnails.MINI_KIND);
        return new Result(bm, Picasso.LoadedFrom.DISK);
    }
}

关于java - 通过单击异步 gridview 中的图像来防止在访问上下文操作菜单时重新加载 Activity ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29997215/