Android 图片压缩处理避免出现oom的方法

1. 通过设置采样率压缩

res资源图片压缩 decodeResource

     public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId, int reqWidth, int reqHeight) {
        // First decode with inJustDecodeBounds=true to check dimensions
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options);

        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeResource(res, resId, options);
    }

uri图片压缩 decodeStream

     public static Bitmap decodeSampledBitmapFromUri(Uri uri, int reqWidth, int reqHeight) {
        Bitmap bitmap = null;
        try {
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
       BitmapFactory.decodeStream(getContentResolver().openInputStream(uri), null, options);
        options.inSampleSize = BitmapUtils.calculateInSampleSize(options,
                UtilUnitConversion.dip2px(MyApplication.mContext, reqWidth), UtilUnitConversion.dip2px(MyApplication.mContext, reqHeight));
        options.inJustDecodeBounds = false;

        bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(uri), null, options);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return bitmap;
    }

本地File url图片压缩

    public static Bitmap getloadlBitmap(String load_url, int width, int height) {
        Bitmap bitmap = null;
        if (!UtilText.isEmpty(load_url)) {
            File file = new File(load_url);
            if (file.exists()) {
                FileInputStream fs = null;
                try {
                    fs = new FileInputStream(file);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
                if (null != fs) {
                    try {
                        BitmapFactory.Options opts = new BitmapFactory.Options();
                        opts.inJustDecodeBounds = true;
                        BitmapFactory.decodeFileDescriptor(fs.getFD(), null, opts);
                        opts.inDither = false;
                        opts.inPurgeable = true;
                        opts.inInputShareable = true;
                        opts.inTempStorage = new byte[32 * 1024];
                        opts.inSampleSize = BitmapUtils.calculateInSampleSize(opts,
                                UtilUnitConversion.dip2px(MyApplication.mContext, width), UtilUnitConversion.dip2px(MyApplication.mContext, height));
                        opts.inJustDecodeBounds = false;

                        bitmap = BitmapFactory.decodeFileDescriptor(fs.getFD(),
                                null, opts);
                    } catch (IOException e) {
                        e.printStackTrace();
                    } finally {
                        if (null != fs) {
                            try {
                                fs.close();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        }
        return bitmap;
    }

根据显示的图片大小进行SampleSize的计算

public int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        if (reqWidth == 0 || reqHeight == 0) {
            return 1;
        }

        // Raw height and width of image
        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;
    }

附:宽高dp值转px的工具类

    /**
     * dip 装换成 px
     * 
     * @作者 zhuofq
     * @创建时间   
     * @param context
     * @param dipValue
     * @return int
     */
    public static int dip2px(Context context, float dipValue) {
        int num = 0;
        if (context != null) {
            final float scale = context.getResources().getDisplayMetrics().density;
            num = (int) (dipValue * scale + 0.5f);
        }
        return num;
    }

以上三种工具类的调用方式（设工具类名为UtilBitmap，ImageView宽高100dp）：

mImageView.setImageBitmap(UtilBitmap.decodeSampledBitmapFromResource(getResources(), R.id.myImage, 100, 100));

Bitmap bitmap = UtilBitmap.decodeSampledBitmapFromUri(cropFileUri, 100, 100);

mImageView.setImageBitmap(mContext, mImage,
                UtilBitmap.getloadlBitmap(url, 100, 100),
                R.drawable.ic_login_head, true);

2. 质量压缩：指定图片缩小到xkb以下

    // 压缩到100kb以下
    int maxSize = 100 * 1024;
    public static Bitmap getBitmapByte(Bitmap oriBitmap, int maxSize) {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        oriBitmap.compress(Bitmap.CompressFormat.JPEG, 100, out);

        byte[] fileBytes = out.toByteArray();

        int be = (maxSize * 100) / fileBytes.length;

        if (be > 100) {
            be = 100;
        }
        out.reset();
        oriBitmap.compress(Bitmap.CompressFormat.JPEG, be, out);
        return oriBitmap;
    }

3. 单纯获取图片宽高避免oom的办法

itmapFactory.Options这个类，有一个字段叫做 inJustDecodeBounds 。SDK中对这个成员的说明是这样的：

If set to true, the decoder will return null (no bitmap), but the out...

也就是说，如果我们把它设为true，那么BitmapFactory.decodeFile(String path, Options opt)并不会真的返回一个Bitmap给你，它仅仅会把它的宽，高取回来给你，这样就不会占用太多的内存，也就不会那么频繁的发生OOM了。

    /**
     * 根据res获取Options，来获取宽高options.outWidth和options.outHeight
     * @param res
     * @param resId
     * @return
     */
    public static BitmapFactory.Options decodeOptionsFromResource(Resources res, int resId) {
        // First decode with inJustDecodeBounds=true to check dimensions
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options);
        return options;
    }