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。這往往是由於圖片過大造成的。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);
設置inJustDecodeBounds為true后，decodeFile並不分配空間，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) {
}