Android out of memory exception with bitmaps

问题

First off, I have read many posts and articles about out of memory exceptions but none of them have helped with my situation. What I'm trying to do is load an image from the sd card but scale it to an exact pixel size.

I first get the width and height of the image and calculate the sample size:

    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(backgroundPath, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, getWidth(), getHeight());

Here's how I get the sample size (although its not really relevant):

public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {

    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;

    // NOTE: we could use Math.floor here for potential better image quality
    // however, this also results in more out of memory issues
    if (height > reqHeight || width > reqWidth) {
        if (width > height) {
            inSampleSize = Math.round((float)height / (float)reqHeight);
        } else {
            inSampleSize = Math.round((float)width / (float)reqWidth);
        }
    }

    return inSampleSize;
}

Now that I have a sample size I load the image from disk to an approximate size (sample size):

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    options.inPurgeable = true;
    Bitmap bmp = BitmapFactory.decodeFile(backgroundPath, options);

Now, I scale this bitmap that I have created to the exact size I need and clean up:

    // scale the bitmap to the exact size we need
    Bitmap editedBmp = Bitmap.createScaledBitmap(bmp, (int) (width * scaleFactor), (int) (height * scaleFactor), true); 

    // clean up first bitmap
    bmp.recycle();
    bmp = null;
    System.gc();    // I know you shouldnt do this, but I'm desperate 

The above step is usually get my out of memory exception. Does anyone know a way to load an exact size bitmap from disk to avoid having to create two separate bitmaps like above?

Also, it seems like more exceptions occur when the user runs this code for a second time (sets a new image). However, I make sure to unload the drawable that was created from the bitmap which allows it to be garbage collected before this code is run again.

Any suggestions?

Thanks, Nick

回答1:

In your case there's no need to create the intermediate bitmap after you've performed the first decode. Since you're drawing to to a Canvas, you can use either the following methods (whichever you find most convenient) to scale the image to the perfect size.

drawBitmap(Bitmap bitmap, Rect src, Rect dst, Paint paint)

drawBitmap(Bitmap bitmap, Matrix matrix, Paint paint)

回答2:

Maybe this method would be helpful, I think I pulled it off of stackoverflow myself. It solved my out of memory exception issue.

private Bitmap decodeFile(File f){
    try {
        //Decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(f),null,o);

        //The new size we want to scale to
        final int REQUIRED_SIZE=250;

        //Find the correct scale value. It should be the power of 2.
        int scale=1;
        while(o.outWidth/scale/2>=REQUIRED_SIZE && o.outHeight/scale/2>=REQUIRED_SIZE)
            scale*=2;

        //Decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize=scale;
        return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
    } catch (FileNotFoundException e) {}

    return null;
} 

来源：https://stackoverflow.com/questions/15030542/android-out-of-memory-exception-with-bitmaps