IceImageUtils.java

package ovh.ice.icecons;

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.view.View;
import android.widget.ImageView;

import java.lang.ref.WeakReference;

public class IceImageUtils {

    public static void bitmapLoadAsync( ImageView imageView, Resources res, int resId, int width, int height ) {

        BitmapWorkerTask task = new BitmapWorkerTask( imageView );

        task.res = res;
        task.resId = resId;
        task.width = width;
        task.height = height;

        task.execute( resId );
    }

    public static Bitmap bitmapLoad( Resources res, int resId, int width, int height ) {

        // calc scale, load appropriately sampled bitmap from given resource

        BitmapFactory.Options resOptions = new BitmapFactory.Options();
        resOptions.inJustDecodeBounds = true;
        BitmapFactory.decodeResource( res, resId, resOptions );

        int resHeight = resOptions.outHeight;
        int resWidth = resOptions.outWidth;

        float xScale = (float) width / (float) resWidth;
        float yScale = (float) height / (float) resHeight;
        float scale = Math.max( xScale, yScale );

        if( width == 0 ) width = Math.round( resWidth / scale );
        else if( height == 0 ) height = Math.round( resHeight / scale );

        resOptions.inSampleSize = sampleSize( scale );
        resWidth /= resOptions.inSampleSize;
        resHeight /= resOptions.inSampleSize;
        resOptions.inJustDecodeBounds = false;

        Bitmap rawBitmap = BitmapFactory.decodeResource( res, resId, resOptions );

        // compare aspect ratio and crop

        rawBitmap = bitmapCrop( rawBitmap, width, height, resWidth, resHeight );

        // scale to desired size

        return Bitmap.createScaledBitmap( rawBitmap, width, height, true );
    }

    // calc sample size for scaled resource loading

    private static int sampleSize( float scale ) {

        int size = 1;

        while( scale < 0.5f ) {

            size *= 2;
            scale *= 2;
        }

        return size;
    }

    // crop bitmap to chosen aspect ratio

    private static Bitmap bitmapCrop( Bitmap rawBitmap, int width, int height, int resWidth, int resHeight ) {

        int cropX, cropY, cropWidth, cropHeight;

        float xScale = (float) width / (float) resWidth;
        float yScale = (float) height / (float) resHeight;
        float scale = Math.max( xScale, yScale );

        if( xScale >= yScale ) {
            cropWidth = Math.round( resWidth );
            cropX = 0;
            cropHeight = Math.round( height / scale );
            cropY = ( resHeight - cropHeight ) / 2;
        }
        else {
            cropWidth = Math.round( width / scale );
            cropX = ( resWidth - cropWidth ) / 2;
            cropHeight = Math.round( resHeight );
            cropY = 0;
        }

        return Bitmap.createBitmap( rawBitmap, cropX, cropY, cropWidth, cropHeight );
    }
}

class BitmapWorkerTask extends AsyncTask< Integer, Void, Bitmap > {

    private final WeakReference< ImageView > imageViewReference;

    Resources res;
    int resId, width, height;

    public BitmapWorkerTask( ImageView imageView ) {

        imageViewReference = new WeakReference<ImageView>(imageView);
    }

    // Decode image in background

    @Override
    protected Bitmap doInBackground( Integer... parameters ) {

        return IceImageUtils.bitmapLoad( res, resId, width, height );
    }

    // Check if image view still exists and set bitmap

    @Override
    protected void onPostExecute( Bitmap bitmap ) {

        if ( imageViewReference != null && bitmap != null ) {

            final ImageView imageView = imageViewReference.get();

            if ( imageView != null ) {

                imageView.setImageBitmap(bitmap);

                imageView.setAlpha( 0f );
                imageView.setVisibility( View.VISIBLE );

                imageView.animate()
                        .alpha(1f)
                        .setDuration( res.getInteger( android.R.integer.config_mediumAnimTime ) )
                        .setListener( null );
            }
        }
    }
}