Android Bitmap在不加载图片的前提获取宽高

来源：互联网发布：cab格式软件编辑：程序博客网时间：2024/06/05 02:06

代码参考：

 /**      * 根据View(主要是ImageView)的宽和高来获取图片的缩略图      * @param path      * @param viewWidth      * @param viewHeight      * @return      */      private Bitmap decodeThumbBitmapForFile(String path, int viewWidth, int viewHeight){          BitmapFactory.Options options = new BitmapFactory.Options();          //设置为true,表示解析Bitmap对象，该对象不占内存          options.inJustDecodeBounds = true;          BitmapFactory.decodeFile(path, options);          //设置缩放比例          options.inSampleSize = computeScale(options, viewWidth, viewHeight);                    //设置为false,解析Bitmap对象加入到内存中          options.inJustDecodeBounds = false;                    return BitmapFactory.decodeFile(path, options);      }                  /**      * 根据View(主要是ImageView)的宽和高来计算Bitmap缩放比例。默认不缩放      * @param options      * @param width      * @param height      */      private int computeScale(BitmapFactory.Options options, int viewWidth, int viewHeight){          int inSampleSize = 1;          if(viewWidth == 0 || viewHeight == 0){              return inSampleSize;          }          int bitmapWidth = options.outWidth;          int bitmapHeight = options.outHeight;                    //假如Bitmap的宽度或高度大于我们设定图片的View的宽高，则计算缩放比例          if(bitmapWidth > viewWidth || bitmapHeight > viewWidth){              int widthScale = Math.round((float) bitmapWidth / (float) viewWidth);              int heightScale = Math.round((float) bitmapHeight / (float) viewWidth);                            //为了保证图片不缩放变形，我们取宽高比例最小的那个              inSampleSize = widthScale < heightScale ? widthScale : heightScale;          }          return inSampleSize;      }

另外可参照：

BitmapFactory.Options options = new BitmapFactory.Options();                  /**         * 最关键在此，把options.inJustDecodeBounds = true;         * 这里再decodeFile()，返回的bitmap为空，但此时调用options.outHeight时，已经包含了图片的高了         */         options.inJustDecodeBounds = true;         Bitmap bitmap = BitmapFactory.decodeFile("/sdcard/test.jpg", options); // 此时返回的bitmap为null         /**         *options.outHeight为原始图片的高         */         Log.e("Test", "Bitmap Height == " + options.outHeight);

根据这些方法，可以在实际加载Bitmap图片之前根据需要设置图片缩小为原来的（1/2,1/4,1/8,1/16..）

下面是Android源码中关于 inSampleSize的说明:

<span style="background-color: rgb(51, 255, 51);">public int inSampleSize</span>Added in API level 1If set to a value > 1, requests the decoder to subsample the original image, returning a smaller image to save memory. The sample size is the number of pixels in either dimension that correspond to a single pixel in the decoded bitmap. For example, inSampleSize == 4 returns an image that is 1/4 the width/height of the original, and 1/16 the number of pixels. Any value <= 1 is treated the same as 1. Note: the decoder uses a final value based on powers of 2,<span style="background-color: rgb(51, 255, 51);"> any other value will be rounded down to the nearest power of 2</span>.

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