Android - downloading image from web, saving to internal memory in location private to app, displaying for list item

问题

What I'm trying to do is this: I want my application to download an image from the Internet and save it to the phone's internal memory in a location that is private to the application. If there is no image available for the list item (i.e. it can't be found on the Internet), I want a default placeholder image to display. This is the image that I have defined in my list_item_row.xml file as the default.

In my ListActivity file, I am calling an instance of a CustomCursorAdapter class I have written. It is in CustomCursorAdapter where I am iterating through all the list items and defining what content needs to be mapped to the views, including the image file by trying to read it from internal memory.

I've seen several questions on this subject, but the examples either are specific to external phone memory (e.g. SDCard), involve saving strings instead of images, or involve using Bitmap.CompressFormat to reduce the resolution of the file (which is unnecessary in my case, as these images will be small thumbnails of already-small resolution). Trying to piece together code from each example has been difficult, hence my asking about my specific example.

At the moment, I believe I've written valid code, but no image is displaying for my list items, including the default placeholder image. I don't know if the problem is being caused by invalid download/save code, or invalid read code - it doesn't help that I don't know how to check internal memory to see if the image exists.

Anyways, here's my code. Any help would be greatly appreciated.

ProductUtils.java

public static String productLookup(String productID, Context c) throws IOException {
    URL url = new URL("http://www.samplewebsite.com/" + productID + ".jpg");
    URLConnection connection = url.openConnection();
    InputStream input = connection.getInputStream();
    FileOutputStream output = 
        c.openFileOutput(productID + "-thumbnail.jpg", Context.MODE_PRIVATE);
    byte[] data = new byte[1024];

    output.write(data);
    output.flush();
    output.close();
    input.close();
}

CustomCursorAdapter.java

public class CustomCursorAdapter extends CursorAdapter {
    public CustomCursorAdapter(Context context, Cursor c) {
        super(context, c);
    }

    @Override
    public void bindView(View view, Context context, Cursor cursor) {
        ImageView thumbnail = (ImageView) view.findViewById(R.id.thumbnail);

        String fileName = 
                cursor.getString(cursor.getColumnIndex(DbAdapter.KEY_IMAGE_FILE_PATH));

        Bitmap bMap = BitmapFactory.decodeFile(fileName);
        thumbnail.setImageBitmap(bMap);
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        LayoutInflater inflater = LayoutInflater.from(context);
        View v = inflater.inflate(R.layout.list_item_row, parent, false);
        bindView(v, context, cursor);
        return v;
    }
}

回答1:

it seems that some code is left out, I re-wrote it like this:

ProductUtils.java

public static String productLookup(String productID, Context c) throws IOException {

    URL url = new URL("http://www.samplewebsite.com/" + productID + ".jpg");

    InputStream input = null;
    FileOutputStream output = null;

    try {
        String outputName = productID + "-thumbnail.jpg";

        input = url.openConnection().getInputStream();
        output = c.openFileOutput(outputName, Context.MODE_PRIVATE);

        int read;
        byte[] data = new byte[1024];
        while ((read = input.read(data)) != -1)
            output.write(data, 0, read);

        return outputName;

    } finally {
        if (output != null)
            output.close();
        if (input != null)
            input.close();
    }
}

回答2:

Looks like simply referring to the image file name when trying to read it was not enough, and I had to call getFilesDir() to get the path of the file storage. Below is the code I used:

String path = context.getFilesDir().toString();
String fileName = cursor.getString(cursor.getColumnIndex(DbAdapter.KEY_PRODUCT_ID));

if (fileName != null && !fileName.equals("")) {
    Bitmap bMap = BitmapFactory.decodeFile(path + "/" + fileName);
    if (bMap != null) {
        thumbnail.setImageBitmap(bMap);
    }
}

回答3:

void  writeToFile(Bitmap _bitmapScaled)
    {
        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
        _bitmapScaled.compress(Bitmap.CompressFormat.PNG, 40, bytes);
        try{
        File f;
        //you can create a new file name "test.jpg" in sdcard folder.
        if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
            f =new File(android.os.Environment.getExternalStorageDirectory(),"FamilyLocator/userimages/"+imageName);
        else
         f = new File(Environment.getDataDirectory(),"FamilyLocator/userimages/"+imageName);

        f.createNewFile();
        //write the bytes in file
        FileOutputStream fo = new FileOutputStream(f);
        fo.write(bytes.toByteArray());
        // remember close de FileOutput
        fo.close();
        }catch(Exception e){e.printStackTrace();}
    }

来源：https://stackoverflow.com/questions/4181566/android-downloading-image-from-web-saving-to-internal-memory-in-location-priv