Android Training精要（五）讀取Bitmap對象實際的尺寸和類型

讀取Bitmap對象實際的尺寸和類型

BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(getResources(), R.id.myimage, options);
int imageHeight = options.outHeight;
int imageWidth = options.outWidth;
String imageType = options.outMimeType;

計算inSampleSize來控制縮放比例,值最好設為2的指數.例如inSampleSize為2,則長和寬縮短為原來的1/2,這樣整個圖片縮小為原來的1/4.

完整的從資源加載Bitmap的代碼

public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
        int reqWidth, int reqHeight) {
    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(res, resId, options);
    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(res, resId, options);
}

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;    

    	if (height > reqHeight || width > reqWidth) {
    		final int halfHeight = height / 2;
    		final int halfWidth = width / 2;
    		// Calculate the largest inSampleSize value that is a power of 2 and keeps both
    		// height and width larger than the requested height and width.
    		while ((halfHeight / inSampleSize) > reqHeight
    				&& (halfWidth / inSampleSize) > reqWidth) {
    			inSampleSize *= 2;
    			}
    		}
    	return inSampleSize;
    }