Android 异步获取网络图片并处理导致内存溢出问题解决方法

<uses-permission android:name="android.permission.internet" />

import java.io.bytearrayoutputstream;
import java.io.ioexception;
import java.io.inputstream;
import java.net.malformedurlexception;
import java.net.url;
import android.graphics.bitmap;
import android.graphics.bitmapfactory;
import android.os.asynctask;
import android.widget.imageview;
public class imagedownloadtask extends asynctask<object, object, bitmap> {
private imageview imageview = null;
/***
* 这里获取到手机的分辨率大小
* */
public void setdisplaywidth(int width) {
_displaywidth = width;
}
public int getdisplaywidth() {
return _displaywidth;
}
public void setdisplayheight(int height) {
_displayheight = height;
}
public int getdisplayheight() {
return _displayheight;
}
public int getdisplaypixels() {
return _displaypixels;
}
private int _displaywidth = 480;
private int _displayheight = 800;
private int _displaypixels = _displaywidth * _displayheight;
@override
protected bitmap doinbackground(object... params) {
// todo auto-generated method stub
bitmap bmp = null;
imageview = (imageview) params[1];
try {
string url = (string) params[0];
bmp = getbitmap(url, _displaypixels,true);
} catch (exception e) {
return null;
}
return bmp;
}
protected void onpostexecute(bitmap result) {
if (imageview != null&&result!=null) {
imageview.setimagebitmap(result);
if (null != result && result.isrecycled() == false)
system.gc();
}
}
/**
* 通过url获得网上图片。如:http://www.xxxxxx.com/xx.jpg
* */
public bitmap getbitmap(string url, int displaypixels, boolean isbig) throws malformedurlexception, ioexception {
bitmap bmp = null;
bitmapfactory.options opts = new bitmapfactory.options();
inputstream stream = new url(url).openstream();
byte[] bytes = getbytes(stream);
//这3句是处理图片溢出的begin( 如果不需要处理溢出直接 opts.insamplesize=1;)
opts.injustdecodebounds = true;
bitmapfactory.decodebytearray(bytes, 0, bytes.length, opts);
opts.insamplesize = computesamplesize(opts, -1, displaypixels);
//end
opts.injustdecodebounds = false;
bmp = bitmapfactory.decodebytearray(bytes, 0, bytes.length, opts);
return bmp;
}
/**
* 数据流转成btyle[]数组
* */
private byte[] getbytes(inputstream is) {
bytearrayoutputstream baos = new bytearrayoutputstream();
byte[] b = new byte[2048];
int len = 0;
try {
while ((len = is.read(b, 0, 2048)) != -1) {
baos.write(b, 0, len);
baos.flush();
}
} catch (ioexception e) {
e.printstacktrace();
}
byte[] bytes = baos.tobytearray();
return bytes;
}
/****
* 处理图片bitmap size exceeds vm budget （out of memory 内存溢出）
*/
private 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 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 lowerbound;
}
if ((maxnumofpixels == -1) && (minsidelength == -1)) {
return 1;
} else if (minsidelength == -1) {
return lowerbound;
} else {
return upperbound;
}
}
}

@override
public void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.main);
imagedownloadtask imgtask =new imagedownloadtask();
/**这里是获取手机屏幕的分辨率用来处理 图片 溢出问题的。begin*/
displaymetrics dm = new displaymetrics();
getwindowmanager().getdefaultdisplay().getmetrics(dm);
imgtask.setdisplaywidth(dm.widthpixels);
imgtask.setdisplayheight(dm.heightpixels);
//end
imageview imageview_test= (imageview)findviewbyid(r.id.imageview_test);
imgtask.execute("http://pic.qukantu.com/big/7515/201201031116491.jpg",imageview_test);
}