因为图片的尺寸千差百异,要想加载不同的图片,又要保证不影响整体布局的美观,我们可以通过计算需要的尺寸来加载图片。
直接上代码:
public static synchronized Bitmap decodeSampledBitmapFromStream( InputStream in, int reqWidth, int reqHeight) { // First decode with inJustDecodeBounds=true to check dimensions final BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeStream(in, null, options); // Calculate inSampleSize options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // Decode bitmap with inSampleSize set options.inJustDecodeBounds = false; return BitmapFactory.decodeStream(in, null, options); } /** * Calculate an inSampleSize for use in a {@link BitmapFactory.Options} * object when decoding bitmaps using the decode* methods from * {@link BitmapFactory}. This implementation calculates the closest * inSampleSize that will result in the final decoded bitmap having a width * and height equal to or larger than the requested width and height. This * implementation does not ensure a power of 2 is returned for inSampleSize * which can be faster when decoding but results in a larger bitmap which * isn't as useful for caching purposes. * * @param options * An options object with out* params already populated (run * through a decode* method with inJustDecodeBounds==true * @param reqWidth * The requested width of the resulting bitmap * @param reqHeight * The requested height of the resulting bitmap * @return The value to be used for inSampleSize */ public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) { // Raw height and width of image final int height = options.outHeight; final int width = options.outWidth; int inSampleSize = 1; //先根据宽度进行缩小 while (width / inSampleSize > reqWidth) { inSampleSize++; } //然后根据高度进行缩小 while (height / inSampleSize > reqHeight) { inSampleSize++; } return inSampleSize; }
该方法通过指定大小来加载图片,并保证加载的图片宽、高均不超过指定的大小。
来看看inSampleSize的函义:
/** * If 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 will try to fulfill this request, but the resulting bitmap * may have different dimensions that precisely what has been requested. * Also, powers of 2 are often faster/easier for the decoder to honor. */ public int inSampleSize;
当inSampleSize大于1时,解码器会将宽和高分别缩小inSampleSize倍。
上述calculateInSampleSize方法正是通过将宽与高进行比对得出的inSampleSize值。