android开发实例-AsyncTask
啥状况啊，为什么上传图片浏览器就会刷新啊，文章都掉了好几次了。打开自动保存的内容，然后就显示在那边，返回键也木有。我决定不废话了。。
1.activity_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".MainActivity" > <TextView android:id="@+id/ShowMsg" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:text="@string/hello_world" /> <Button android:id="@+id/Start" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="下载" /> <Button android:id="@+id/stop" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="停止" /> <ImageView android:id="@+id/imageShow" android:layout_width="fill_parent" android:layout_height="fill_parent" /> </LinearLayout>
2.MainActivity.xml
package com.mythou.asynctask;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import android.media.MediaPlayer;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.app.Dialog;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener
{
private static final String TAG="wxpDeb";
private TextView mShowLogTextView;
private Button mPlayMusicButton;
private Button mStopMusicButton;
private MediaPlayer MediaCtrl;
private DownLoad mDownLoad;
private Context mContext;
private ImageView mNetImageView;
private Bitmap mDownLoadBtBitmap;
Dialog dialog;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = this;
dialog=new Dialog(this);//等待对话框
mShowLogTextView = (TextView)findViewById(R.id.ShowMsg);//下载状态显示
mPlayMusicButton = (Button)findViewById(R.id.Start);//下载按钮
mStopMusicButton = (Button)findViewById(R.id.stop);//停止按钮
mNetImageView = (ImageView)findViewById(R.id.imageShow);//显示图片
mPlayMusicButton.setOnClickListener(this);
mStopMusicButton.setOnClickListener(this);
// Log.w(TAG, "Status:"+mDownLoad.getStatus());
}
public void onClick(View v)
{
if (v==mPlayMusicButton)
{ mShowLogTextView.setText("onPreExecute。。。begin downLoad");
dialog.setTitle("downLoad......");//点击之后立即弹出等待对话框
dialog.show();
mDownLoad = new DownLoad();//注意一定要在这里实例化，否则第一次下载完毕之后如果再次点击下载按钮会报错会出错
new Handler().postDelayed((new Runnable() {
public void run() {
// TODO Auto-generated method stub
//传入下载图片的地
mDownLoad.execute("http://www.baidu.com/img/bdlogo.gif");
}
}), 3000);//为了突出等待效果，延时三秒
Log.w(TAG, "Status:"+mDownLoad.getStatus());
//这个参数难道是doInbackground()方法里的参数param？
Log.i(TAG, "execute() 执行");
}
if (v==mStopMusicButton)
{
mDownLoad.onCancelled();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
private class DownLoad extends AsyncTask<String, Integer, String>
{
//onPreExecute方法在execute()后执行
@Override
protected void onPreExecute()
{
Log.i(TAG, "onPreExecute() enter");
Log.w(TAG, "onPreExecute_start_Status:"+mDownLoad.getStatus());
}
//doInBackground方法内部执行后台任务,不能在里面更新UI，否则有异常。
@Override
protected String doInBackground(String... params)
{ Log.w(TAG, "doInBackground_start_Status:"+mDownLoad.getStatus());
Log.i(TAG, "doInBackground(String... params) enter");
Log.i(TAG, params.toString());
URL imageUrl=null;
try
{
imageUrl=new URL(params[0]);
}
catch (MalformedURLException e)
{
e.printStackTrace();
Log.e(TAG, e.getMessage());
}
try
{
//使用HttpURLConnection打开连接
HttpURLConnection urlConn=(HttpURLConnection)imageUrl.openConnection();
urlConn.setDoInput(true);
urlConn.connect();
//将得到的数据转化成InputStream
InputStream is=urlConn.getInputStream();
//将InputStream转换成Bitmap
mDownLoadBtBitmap=BitmapFactory.decodeStream(is);
is.close();
//不能在这里更新UI,否则有异常
//mNetImageView.setImageBitmap(bitmap);
}catch(IOException e)
{
Log.e(TAG,e.getMessage());
}
Log.w(TAG, "doInBackground_end_Status:"+mDownLoad.getStatus());
return "ok";
}
//onProgressUpdate方法用于更新进度信息
@Override
protected void onProgressUpdate(Integer... progresses)
{
Log.i(TAG, "onProgressUpdate(Integer... progresses) enter");
mShowLogTextView.setText("onProgressUpdate Down loading...");
Log.w(TAG, "onProgressUpdate_end_Status:"+mDownLoad.getStatus());
}
//onPostExecute用于doInBackground执行完后，更新界面UI。
//result是doInBackground返回的结果
@Override
protected void onPostExecute(String result)
{
dialog.dismiss();
Log.w(TAG, "onPostExecute_start_Status:"+mDownLoad.getStatus());
Log.i(TAG, "onPostExecute(Result result) called");
mShowLogTextView.setText("Down load finish result="+result);
mNetImageView.setImageBitmap(mDownLoadBtBitmap);
Log.w(TAG, "onPostExecute_end_Status:"+mDownLoad.getStatus());
}
//onCancelled方法用于取消Task执行，更新UI
@Override
protected void onCancelled()
{
Log.i(TAG, "onCancelled() called");
mShowLogTextView.setText("onCancelled");
mNetImageView.setImageBitmap(null);
//取消之后将imageview清空
}
}
}
插！
