BitmapFactory 方法：decodeFileDescriptor()、decodeFile()

用decodeFileDescriptor()来生成bimap比decodeFile()省内存

FileInputStream is = = new FileInputStream(path);
bmp = BitmapFactory.decodeFileDescriptor(is.getFD(), null, opts);

替换：

Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts);
   imageView.setImageBitmap(bmp);

原因：
查看BitmapFactory的源码，对比一下两者的实现，可以发现decodeFile()最终是以流的方式生成bitmap 

decodeFile源码：

public static Bitmap decodeFile(String pathName, Options opts) {
    Bitmap bm = null;
    InputStream stream = null;
    try {
        stream = new FileInputStream(pathName);
        bm = decodeStream(stream, null, opts);
    } catch (Exception e) {
        /*  do nothing.
            If the exception happened on open, bm will be null.
        */
    } finally {
        if (stream != null) {
            try {
                stream.close();
            } catch (IOException e) {
                // do nothing here
            }
        }
    }
    return bm;
}

decodeFileDescriptor的源码，可以找到native本地方法decodeFileDescriptor，通过底层生成bitmap

decodeFileDescriptor源码：

   public static Bitmap decodeFileDescriptor(FileDescriptor fd, Rect outPadding, Options opts) {
       if (nativeIsSeekable(fd)) {
           Bitmap bm = nativeDecodeFileDescriptor(fd, outPadding, opts);
           if (bm == null && opts != null && opts.inBitmap != null) {
               throw new IllegalArgumentException("Problem decoding into existing bitmap");
           }
           return finishDecode(bm, outPadding, opts);
       } else {
           FileInputStream fis = new FileInputStream(fd);
           try {
               return decodeStream(fis, outPadding, opts);
           } finally {
               try {
                   fis.close();
               } catch (Throwable t) {/* ignore */}
           }
       }
   }

private static native Bitmap nativeDecodeFileDescriptor(FileDescriptor fd,Rect padding, Options opts);