Android 图片处理避免出现oom的方法详解

1. 通过设置采样率压缩

res资源图片压缩 decodeResource

  public 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 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;
  }

调用方式：

代码如下:

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

Bitmap bitmap = decodeSampledBitmapFromUri(cropFileUri);

UtilBitmap.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;
  }

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