Question

我是Android新手。在我的应用程序中，我有一个带有图像的列表视图。我想从url下载图像并存储在路径中（如果图像不存在于路径中）。然后在pathView中设置图像。我做了，但有些问题就在那里。

我的问题：

首次下载时，它会在ListView的每个项目中逐一显示所有图像。最后，设置它设置完美的图像。
从路径设置图像意味着设置图像需要很长时间。

请任何人解决我的问题。

这是我的代码：

我的适配器代码：

 if (ImageStorage.checkifImageExists(ImageStorage.getImageName(list.get(position).imageUrl))) {

        File file = ImageStorage.getImage("/" + ImageStorage.getImageName(list.get(position).imageUrl));
        String path = file.getAbsolutePath();
        Picasso.with(context)
               .load(new File(path))
               .placeholder(R.drawable.loading)
               .error(R.drawable.error)
               .into(holder.menuImage);

    } else {
        new ImageDownloaderTask(list.get(position).imageUrl, holder.menuImage, ImageStorage.getImageName(list.get(position).imageUrl)).execute();
    }

ImageDownloaderTask.java：

public class ImageDownloaderTask extends AsyncTask<Object, Object, Object> {
    private String requestUrl, imagename_;
    private ImageView view;
    private Bitmap bitmap ;
    private FileOutputStream fos;
    public ImageDownloaderTask(String requestUrl, ImageView view, String _imagename_) {
        this.requestUrl = requestUrl;
        this.view = view;
        this.imagename_ = _imagename_ ;
    }
    @Override
    protected Object doInBackground(Object... objects) {
        try {
            URL url = new URL(requestUrl);
            URLConnection conn = url.openConnection();
            InputStream is = new URL( requestUrl ).openStream();
            bitmap = BitmapFactory.decodeStream(is);
        } catch (Exception ex) {
        }
        return null;
    }
    @Override
    protected void onPostExecute(Object o) {
        if(!ImageStorage.checkifImageExists(imagename_))
        {
            view.setImageBitmap(bitmap);
            ImageStorage.saveToSdCard(bitmap, imagename_);
        }
    }
}

ImageStorage.java：

public class ImageStorage {
    public static String saveToSdCard(Bitmap bitmap, String filename) {

        String stored = null;

        File sdcard = Environment.getExternalStorageDirectory();

        File folder = new File(sdcard.getAbsoluteFile(), "tam");//the dot makes this directory hidden to the user
        folder.mkdir();
        File file = new File(folder.getAbsoluteFile(), filename) ;
        if (file.exists())
            return stored ;

        try {
            FileOutputStream out = new FileOutputStream(file);
            bitmap.compress(Bitmap.CompressFormat.PNG, 90, out);
            out.flush();
            out.close();
            stored = "success";
        } catch (Exception e) {
            e.printStackTrace();
        }
        return stored;
    }

    public static File getImage(String imagename) {

        File mediaImage = null;
        try {
            String root = Environment.getExternalStorageDirectory().getAbsolutePath();
            File myDir = new File(root);
            if (!myDir.exists())
                return null;

            mediaImage = new File(myDir.getPath() + "/tam/"+imagename);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return mediaImage;
    }
    public static boolean checkifImageExists(String imagename)
    {
        Bitmap b = null ;
        File file = ImageStorage.getImage("/"+imagename);
        String path = file.getAbsolutePath();
        if (path != null)
            b = BitmapFactory.decodeFile(path);

        if(b == null ||  b.equals(""))
        {
            return false ;
        }
        return true ;
    }

    public static String getImageName(String value){

        String getName[] = value.split("/");
        Log.d("ImagesName",getName[4]);
        return getName[4];
    }
}

Answer 1

您不必创建位图只是检查它是否存在，您只能通过文件检查。

 public static boolean checkifImageExists(String imagename) { 
        File file = ImageStorage.getImage("/" + imagename);
        if (file.exists()) {
            return true;
        } else {
            return false;
        }  
    }

更新部分：

为了更快地执行速度，您可以添加修改

public static boolean checkifImageExists(String imagename)

到

public static File checkifImageExists(String imagename)

如果文件存在则返回文件，否则为null然后你不必再做这一步。

 public static File checkifImageExists(String imagename) {
        File file = ImageStorage.getImage("/" + imagename);
        if (file.exists()) {
            return file;
        } else {
            return null;
        }
    }

在适配器中制作一些chagne。

File file = ImageStorage.checkifImageExists(ImageStorage.getImageName(list.get(position).imageUrl));
        if (file != null) {

            // this step skips
            //File file = ImageStorage.getImage("/" + ImageStorage.getImageName(list.get(position).imageUrl));
            // and this one also skips
            //String path = file.getAbsolutePath();
            Picasso.with(context)
                    .load(file) // why creating new file if you already have same file.
                    .placeholder(R.drawable.loading)
                    .error(R.drawable.error)
                    .into(holder.menuImage);

        } else {
            new ImageDownloaderTask(list.get(position).imageUrl, holder.menuImage, ImageStorage.getImageName(list.get(position).imageUrl)).execute();
        }

<强> onPostExecute（）

    @Override
    protected void onPostExecute(Object o) {
        // Dont check here you dont have image then you are downloading it.its Already checked?
        // rather then check bitmap you are going to save should not be null
        if (bitmap != null) {
            view.setImageBitmap(bitmap);
            ImageStorage.saveToSdCard(bitmap, imagename_);
        }
    }

如何从URL下载图像并存储在路径中，然后在路径中设置imageview中的图像

1 个答案: