BitmapFactory。Options.inSampleSize用法

BitmapFactory.decodeFile(imageFile);

用BitmapFactory解碼一張圖片時，有時會遇到該錯誤。這往往是由于圖片過大造成的。要想正常使用，則需要分配更少的內存空間來存儲。

BitmapFactory.Options.inSampleSize

設置恰當的inSampleSize可以使BitmapFactory分配更少的空間以消除該錯誤。inSampleSize的具體含義請參考SDK文檔。例如：

BitmapFactory.Options opts = new BitmapFactory.Options();opts.inSampleSize = 4;Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

設置恰當的inSampleSize是解決該問題的關鍵之一。BitmapFactory.Options提供了另一個成員inJustDecodeBounds。

BitmapFactory.Options opts = new BitmapFactory.Options();opts.inJustDecodeBounds = true;Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

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設置inJustDecodeBounds為true后，decodeFile并不分配空間，但可計算出原始圖片的長度和寬度，即opts.width和opts.height。有了這兩個參數，再通過一定的算法，即可得到一個恰當的inSampleSize。

查看Android源碼，Android提供了一種動態計算的方法。

public static int computeSampleSize(BitmapFactory.Options options,int minSideLength, int maxNumOfPixels) {int initialSize = computeInitialSampleSize(options, minSideLength,maxNumOfPixels);int roundedSize;if (initialSize <= 8) {roundedSize = 1;while (roundedSize < initialSize) {roundedSize <<= 1;}} else {roundedSize = (initialSize + 7) / 8 * 8;}return roundedSize;}private static int computeInitialSampleSize(BitmapFactory.Options options,int minSideLength, int maxNumOfPixels) {double w = options.outWidth;double h = options.outHeight;int lowerBound = (maxNumOfPixels == -1) ? 1 :(int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));int upperBound = (minSideLength == -1) ? 128 :(int) Math.min(Math.floor(w / minSideLength),Math.floor(h / minSideLength));if (upperBound < lowerBound) {// return the larger one when there is no overlapping zone.return lowerBound;}if ((maxNumOfPixels == -1) &&(minSideLength == -1)) {return 1;} else if (minSideLength == -1) {return lowerBound;} else {return upperBound;}} 使用該算法，就可動態計算出圖片的inSampleSize。BitmapFactory.Options opts = new BitmapFactory.Options();opts.inJustDecodeBounds = true;BitmapFactory.decodeFile(imageFile, opts);opts.inSampleSize = computeSampleSize(opts, -1, 128*128); opts.inJustDecodeBounds = false;try {Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts);imageView.setImageBitmap(bmp);} catch (OutOfMemoryError err) {}

轉載于:https://www.cnblogs.com/lost-in-code/archive/2012/04/06/2435325.html

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