在ImageView中显示从数据库下载的图像

Question

I'm developing an Android app which allows users to upload/download images to and from a database (powered by Amazon AWS). The problem I'm facing is that I can successfully download the files to a directory

/storage/emulated/0/data/myfile.jpg

But I cannot display them as a new ImageView.

Here are my methods that deal with displaying the methods. Note that RefreshFeedTask.downloadedFiles is a List of Bitmaps as shown here:

 do {
        objectListing = s3Client.listObjects(listObjectsRequest);
        for (S3ObjectSummary objectSummary :
                objectListing.getObjectSummaries()) {

           keys.add(objectSummary.getKey());
        }
        listObjectsRequest.setMarker(objectListing.getNextMarker());
    } while (objectListing.isTruncated());

    Iterator<String> o = keys.iterator();

    while(o.hasNext())
    {

        String n = o.next();
        File file = new File(Environment.getExternalStorageDirectory()+"/data/", n);
        if(!file.exists())
        {
            try {
                file.createNewFile();

            } catch (IOException e) {
                e.printStackTrace();
            }
        }


        TransferObserver observer = transferUtility.download(
                existingBucketName,
                n,
                file);

        Bitmap m = BitmapFactory.decodeFile(file.getAbsolutePath());

---

 private void refreshFeed()
{

    new RefreshFeedTask(this).start();
    for(Bitmap f : RefreshFeedTask.downloadedFiles)
    {
        displayImage(f);
    }

}

private void displayImage(Bitmap f){

    ImageView myImage = new ImageView(this);
    myImage.setImageBitmap(f);
    myImage.setVisibility(View.VISIBLE);
    Log.i("Background","Displaying file");

}

Any help is appreciated, as I am somewhat new to Android development, but not Java development.

Answer 1

One issue that you have here is Ownership.

Advise: That file you just downloaded to that location, your app may not own that location. If this is a closed ecosystem where you are the sole user and owner of that file, you should probably create an application specific directory upon running the application.

The best way to display something that you do not own in the Sdcard is to use the MediaStore API in Android to access them. You need a URI to the right path and just doing an absolute path is not generally advised, especially for image assets.

A good example of this is here: https://dzone.com/articles/displaying-images-sd-card

Answer 2

Looks like you have not added you new ImageView to any view, try adding your new ImageView to any container to display it.

parentLayout.addView(theNewImageView);

Another tip: You can try Glide if you want to display many images more efficiently.