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;
public static int calculateInSampleSize(
BitmapFactory.Options options,int reqWidth,int reqHeight){
// Raw height and width of image
finalint height = options.outHeight;
finalint width = options.outWidth;
int inSampleSize =1;
if(height > reqHeight || width > reqWidth){
finalint halfHeight = height /2;
finalint 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;
}
在decode的时候先设置options.inJustDecodeBounds =true，获取到图片参数后再设置为false，这就是decode时的技巧，下面就把完整代码贴出来，可以作为工具方法来使用：
public static Bitmap decodeSampledBitmapFromResource(Resources res,int resId,
int reqWidth,int reqHeight){
// First decode with inJustDecodeBounds=true to check dimensions
finalBitmapFactory.Options options =newBitmapFactory.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;
returnBitmapFactory.decodeResource(res, resId, options);
}
上面的方法来自于google官网，没必要进行修改，这就是程序员的拿来主义吧，关键在于要知道为什么这么写。下面是我自己写的一个方法可以直接拿来当工具用。
/**
* 对图片进行压缩，主要是为了解决控件显示过大图片占用内存造成OOM问题,一般压缩后的图片大小应该和用来展示它的控件大小相近.
*
* @param context 上下文
* @param resId 图片资源Id
* @param reqWidth 期望压缩的宽度
* @param reqHeight 期望压缩的高度
* @return 压缩后的图片
*/
public static Bitmap compressBitmapFromResourse(Context context, int resId, int reqWidth, int reqHeight) {
final BitmapFactory.Options options = new BitmapFactory.Options();
/*
* 第一次解析时，inJustDecodeBounds设置为true，
* 禁止为bitmap分配内存，虽然bitmap返回值为空，但可以获取图片大小
*/
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(context.getResources(), resId, options);
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int heightRatio = Math.round((float) height / (float) reqHeight);
final int widthRatio = Math.round((float) width / (float) reqWidth);
inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
}
options.inSampleSize = inSampleSize;
// 使用计算得到的inSampleSize值再次解析图片
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(context.getResources(), resId, options);
}
原文：http://my.oschina.net/u/2335607/blog/404550