android实现图片压缩

android在开发时常用到的图片的压缩后在操作，实现类BitmapUtils.java

import android.app.Activity;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.widget.ImageView;

/**
 * @author Administrator
 * @content
 * @date 2018/1/26
 */

public class BitmapUtils {
    /**
     * @description 计算图片的压缩比率
     *
     * @param options 参数
     * @param reqWidth 目标的宽度
     * @param reqHeight 目标的高度
     * @return
     */
    private static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        // 源图片的高度和宽度
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;
        if (height > reqHeight || width > reqWidth) {
            final int halfHeight = height / 2;
            final int halfWidth = width / 2;
            // Calculate the largest inSampleSize value that is a power of 2 and keeps both
            // height and width larger than the requested height and width.
            while (halfHeight / inSampleSize > reqHeight && halfWidth / inSampleSize > reqWidth) {
                inSampleSize *= 2;
            }
        }
        return inSampleSize;
    }

    /**
     * @description 通过传入的bitmap，进行压缩，得到符合标准的bitmap
     *
     * @param src
     * @param dstWidth
     * @param dstHeight
     * @return
     */
    private static Bitmap createScaleBitmap(Bitmap src, int dstWidth, int dstHeight, int inSampleSize) {
        Bitmap dst = Bitmap.createScaledBitmap(src, dstWidth, dstHeight, false);
        if (src != dst) { // 如果没有缩放，那么不回收
            src.recycle(); // 释放Bitmap的native像素数组
        }
        return dst;
    }

    /**
     * @description 从Resources中加载图片
     *
     * @param res
     * @param resId
     * @param reqWidth
     * @param reqHeight
     * @return
     */
    public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true; // 设置成了true,不占用内存，只获取bitmap宽高
        BitmapFactory.decodeResource(res, resId, options); // 读取图片长宽，目的是得到图片的宽高
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // 调用上面定义的方法计算inSampleSize值
        // 使用获取到的inSampleSize值再次解析图片
        options.inJustDecodeBounds = false;
        Bitmap src = BitmapFactory.decodeResource(res, resId, options); // 载入一个稍大的缩略图
        return createScaleBitmap(src, reqWidth, reqHeight, options.inSampleSize); // 通过得到的bitmap，进一步得到目标大小的缩略图
    }

    /**
     * @description 从SD卡上加载图片
     *
     * @param pathName
     * @param reqWidth
     * @param reqHeight
     * @return
     */
    public static Bitmap decodeSampledBitmapFromFile(String pathName, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(pathName, options);
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        Bitmap src = BitmapFactory.decodeFile(pathName, options);
        return createScaleBitmap(src, reqWidth, reqHeight, options.inSampleSize);
    }

    /**
     * 大图压缩
     * @param context
     * @param resourcesId
     * @param imageView
     */
    public static void loadBitmap(Activity context, int resourcesId, ImageView imageView) {
        int bmSize = 0;
        Bitmap bm = null;
        if (true) {
            // 通过工具类来产生一个符合ImageView的缩略图，因为ImageView的大小是50x50，所以这里得到的缩略图也应该是一样大小的
            bm = BitmapUtils.decodeSampledBitmapFromResource(context.getResources(), resourcesId, imageView.getWidth(), imageView.getHeight());
        } else {
            // 直接加载原图
            bm = BitmapFactory.decodeResource(context.getResources(), resourcesId);
        }
        imageView.setImageBitmap(bm);
        bmSize += bm.getByteCount(); // 得到bitmap的大小
        int kb = bmSize / 1024;
        int mb = kb / 1024;
    }
}