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：

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;
  }

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。