安卓ViewPager卡顿问题

Question

ViewPager加载了五张大图，每张图都是2M，左右翻页会很卡很卡，该怎么解决

Answer 1

是本地图片吗？可以先展示缩略图，再展示原始图。加载都在子线程中进行。

读取缩略图的方法：

  /**
     * 通过限制加载图片的宽度和高度，限制不加载超大图片
     *
     * @param dst    图片文件
     * @param width  宽度
     * @param height 高度
     */
    public static Bitmap getBitmapFromFile(File dst, int width, int height) {
        if (null != dst && dst.exists()) {
            BitmapFactory.Options opts = null;
            if (width > 0 && height > 0) {
                opts = new BitmapFactory.Options();
                //设置inJustDecodeBounds为true后，decodeFile并不分配空间，此时计算原始图片的长度和宽度
                opts.inJustDecodeBounds = true;
                BitmapFactory.decodeFile(dst.getPath(), opts);
                // 计算图片缩放比例
                final int minSideLength = Math.min(width, height);
                opts.inSampleSize = computeSampleSize(opts, minSideLength, width * height);
                //这里一定要将其设置回false，因为之前我们将其设置成了true
                opts.inJustDecodeBounds = false;
                opts.inInputShareable = true;
                opts.inPurgeable = true;
            }
            try {
                return BitmapFactory.decodeFile(dst.getPath(), opts);
            } catch (OutOfMemoryError e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    private 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;
        }
    }