Android 中使用 AsyncTask 异步读取网络图片

 1.新建android工程asyncloadpicture

新建布局文件activity_main.xml主界面为一个gridview，还有其子项布局文件gridview_item.xml

2.功能主界面mainactivity.java,主代码如下

package com.example.asyncloadpicture;
import java.util.arraylist;
import android.app.activity;
import android.content.context;
import android.graphics.bitmap;
import android.graphics.bitmapfactory;
import android.os.asynctask;
import android.os.bundle;
import android.widget.gridview;
/**
* @author ymw
* @data --
*/
public class mainactivity extends activity {
private gridview gridviewimg;
private arraylist<imageentity> imagelist = new arraylist<imageentity>();
@override
protected void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.activity_main);
gridviewimg = (gridview) findviewbyid(r.id.gridviewimg);
initdata();
}
private void initdata() {
for (int i = ; i < ; i++) {
imageentity b = new imageentity();
b.setimage(bitmapfactory.decoderesource(getresources(),
r.drawable.nopicture));
imagelist.add(b);
}
imageadapter adapter = new imageadapter(getapplicationcontext(),
imagelist);
gridviewimg.setadapter(adapter);
string[] params = {
"http://images.cnitblog.com/i///.png",
"p" };
new imageloadtask(getapplicationcontext(), adapter).execute(params);
}
/** 图片异步加载类 */
public class imageloadtask extends asynctask<string, void, void> {
private imageadapter adapter;
public imageloadtask(context context, imageadapter adapter) {
this.adapter = adapter;
}
@override
protected void doinbackground(string... params) {
string url = params[];// 获取传来的参数，图片uri地址
string p = params[];
for (int i = ; i < adapter.getcount(); i++) {
imageentity bean = (imageentity) adapter.getitem(i);
bitmap bitmap = bitmapfactory.decodestream(request
.handlerdata(url));
bean.setimage(bitmap);
publishprogress(); // 通知去更新ui
}
return null;
}
public void onprogressupdate(void... voids) {
if (iscancelled())
return;
// 更新ui
adapter.notifydatasetchanged();
}
}
/** 图片实体 */
public class imageentity {
private bitmap image;
public bitmap getimage() {
return image;
}
public void setimage(bitmap image) {
this.image = image;
}
}
}

3.gridview列表图片适配器代码imageadapter.java

package com.example.asyncloadpicture;
import java.util.arraylist;
import android.content.context;
import android.view.layoutinflater;
import android.view.view;
import android.view.viewgroup;
import android.widget.baseadapter;
import android.widget.imageview;
import com.example.asyncloadpicture.mainactivity.imageentity;
/**
* 
* @author ymw
* @data -- 图片适配器
*/
public class imageadapter extends baseadapter {
private context _context;
private arraylist<imageentity> _list;
public imageadapter(context context, arraylist<imageentity> imagelist) {
this._context = context;
this._list = imagelist;
}
@override
public int getcount() {
return _list.size();
}
@override
public object getitem(int position) {
return _list.get(position);
}
@override
public long getitemid(int position) {
return position;
}
@override
public view getview(int position, view convertview, viewgroup parent) {
layoutinflater inflater = layoutinflater.from(_context);
convertview = inflater.inflate(r.layout.gridview_item, null);
imageview imgview = (imageview) convertview.findviewbyid(r.id.imgview);
imageentity b = _list.get(position);
// 如果有图片则读取，没有则跳过
if (b.getimage() != null) {
imgview.setimagebitmap(b.getimage());
}
return convertview;
}
}

4.请求网络读取图片的类request.java

package com.example.asyncloadpicture;
import java.io.ioexception;
import java.io.inputstream;
import java.net.url;
import java.net.urlconnection;
import android.graphics.drawable.drawable;
import android.util.log;
/**
* 工具类，主要根据url读取图片返回流的方法
* 
* @author ymw
* 
*/
public class request {
public static inputstream handlerdata(string url) {
inputstream instream = null;
try {
url feedurl = new url(url);
urlconnection conn = feedurl.openconnection();
conn.setconnecttimeout( * );
instream = conn.getinputstream();
} catch (exception e) {
e.printstacktrace();
}
return instream;
}
/** 直接返回drawable对象设置图片 */
public static drawable loadimagefromnetwork(string imageurl) {
drawable drawable = null;
try {
// 可以在这里通过文件名来判断，是否本地有此图片
drawable = drawable.createfromstream(
new url(imageurl).openstream(), "image.jpg");
} catch (ioexception e) {
log.d("test", e.getmessage());
}
if (drawable == null) {
log.d("test", "null drawable");
} else {
log.d("test", "not null drawable");
}
return drawable;
}
}

以上内容给大家介绍了android 中使用 asynctask 异步读取网络图片的相关知识，希望对大家有所帮助！