Android优化图片加载所占用的内存

/**
* 只读取图片的长宽边界,不是真正的加载图片
* @param resourceId
* @return
*/
private BitmapFactory.Options getOptions(int resourceId){
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;//设为true,不是真正的读取图片
BitmapFactory.decodeResource(getResources(),resourceId,options);
int h = options.outHeight;
int w = options.outWidth;
Bitmap bitmap = options.inBitmap;//bitmap为null
Log.d(TAG,"h:"+h+",w:"+w+",bitmap:"+String.valueOf(bitmap==null));
return  options;
}

/**
* 获取图片的缩放比例,根据所需的长宽与实际长宽的比例来计算
* inSampleSize>=1,并且是2的指数,inSampleSize为4,最后实际加载的图片长宽分别为
* 真实长宽的1/4,大小是原来的1/16
* @param options
* @param reqHeight
* @param reqWidth
* @return
*/
private int getInsampleSize(BitmapFactory.Options options,int reqHeight,int reqWidth) {
int height = options.outHeight;
int width = options.outWidth;
int inSampleSize = 1;
if (height>reqHeight || width>reqWidth) {
final int halfHeight = height/2;
final int halfWidth = width/2;
while(halfHeight/inSampleSize>reqHeight && halfWidth/inSampleSize>reqWidth){
inSampleSize *= 2;
}
}
return inSampleSize;
}

/**
* 获取最终加载的bitmap
* @param resourceId
* @param reqHeight
* @param reqWidth
* @return
*/
private Bitmap getBitmap(int resourceId,int reqHeight,int reqWidth){
BitmapFactory.Options options = getOptions(resourceId);
int inSampleSize = getInsampleSize(options,reqHeight,reqWidth);
options.inSampleSize = inSampleSize;
options.inJustDecodeBounds = false;//设置为false真实的加载图片
Bitmap bitmap = BitmapFactory.decodeResource(getResources(),resourceId,options);
return bitmap;
}

Bitmap bitmap = getBitmap(R.mipmap.ic_launcher,32,32);
Bitmap b2 = BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher);
Log.d(TAG,bitmap.getWidth()+":"+bitmap.getHeight());
Log.d(TAG,b2.getWidth()+":"+b2.getHeight());

07-19 09:46:28.469 7169-7169/com.example.archermind.myapplication D/BitmapOptions: 36:36(通过优化方案得到的图片大小)
07-19 09:46:28.469 7169-7169/com.example.archermind.myapplication D/BitmapOptions: 144:144(图片原始大小)