一:AsyncTask(框架)
An asynchronous task is defined by a computation that runs on a background thread and whose result is published on the UI thread. An asynchronous task is defined by 3 generic types, called Params, Progress and Result, and 4 steps, called onPreExecute, doInBackground, onProgressUpdate and onPostExecute.
Params, the type of the parameters sent to the task upon execution. //输入参数Progress, the type of the progress units published during the background computation. //单元参数格式Result, the type of the result of the background computation.//返回参数
Not all types are always used by an asynchronous task. To mark a type as unused, simply use the type
Void:private class MyTask extends AsyncTask<Void, Void, Void> { ... }
package com.example.android_asynctask;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import com.example.android_asynctask.R.string;
import android.R.id;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Entity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.Menu;
import android.view.View;
import android.view.View.OnCreateContextMenuListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.ImageView;
public class MainActivity extends Activity {
private Button button;
private ImageView imageView;
private ProgressDialog progressDialog;
private final String image_path="http://www.baidu.com/img/bdlogo.gif";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button=(Button)this.findViewById(R.id.button1);
imageView=(ImageView)this.findViewById(R.id.imageView1);
progressDialog=new ProgressDialog(this);
progressDialog.setTitle("提示！");
progressDialog.setCancelable(false);
progressDialog.setMessage("正在下载图片，请耐心等候~~~");
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
new MyTast().execute(image_path);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
class MyTast extends AsyncTask<String, Integer, byte[]>{
@Override
protected byte[] doInBackground(String... arg0) {
// TODO Auto-generated method stub
HttpClient httpClient=new DefaultHttpClient();
HttpGet httpGet =new HttpGet(arg0[0]);
byte[] result=null;
try {
HttpResponse httpResponse=httpClient.execute(httpGet);
if(httpResponse.getStatusLine().getStatusCode()==200){
result=EntityUtils.toByteArray(httpResponse.getEntity());
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}finally{
httpClient.getConnectionManager().shutdown();
}
return result;
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
progressDialog.show();
}
//更新ui
@Override
protected void onPostExecute(byte[] result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
Bitmap bitmap=BitmapFactory.decodeByteArray(result, 0,result.length);
imageView.setImageBitmap(bitmap);
progressDialog.dismiss();
}
}
}
必须要添加访问授权<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.INTERNET"/>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.android_asynctask.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
跨线程更新UI的方法在onPostExecute中持行
onProgressUpdate使用AsyncTask的单元参数Progress
package com.example.android_asynctask;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import com.example.android_asynctask.R.string;
import android.R.id;
import android.R.integer;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.content.Entity;
import android.database.DatabaseUtils;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.Menu;
import android.view.View;
import android.view.View.OnCreateContextMenuListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.ImageView;
public class MainActivity extends Activity {
private Button button;
private ImageView imageView;
private ProgressDialog progressDialog;
private final String image_path="http://www.baidu.com/img/bdlogo.gif";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button=(Button)this.findViewById(R.id.button1);
imageView=(ImageView)this.findViewById(R.id.imageView1);
progressDialog=new ProgressDialog(this);
progressDialog.setTitle("提示！");
progressDialog.setCancelable(false);
progressDialog.setMessage("正在下载图片，请耐心等候~~~");
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
new MyTast().execute(image_path);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
class MyTast extends AsyncTask<String, Integer, byte[]>{
@Override
protected byte[] doInBackground(String... arg0) {
// TODO Auto-generated method stub
HttpClient httpClient=new DefaultHttpClient();
HttpGet httpGet =new HttpGet(arg0[0]);
byte[] result=null;//图片的所以内容
InputStream inputStream =null;
ByteArrayOutputStream outputStream=new ByteArrayOutputStream();
try {
HttpResponse httpResponse=httpClient.execute(httpGet);
long file_length=httpResponse.getEntity().getContentLength();
int total_length=0;
byte[] data=new byte[1024];
int len=0;
if(httpResponse.getStatusLine().getStatusCode()==200){
//result=EntityUtils.toByteArray(httpResponse.getEntity());
inputStream=httpResponse.getEntity().getContent();
while ((len=inputStream.read(data))!=-1) {
total_length+=len;
int process_value=(int)((total_length/(float)file_length)*100);
publishProgress(process_value);//发布刻度单位
outputStream.write(data,0,len);
}
}
result=outputStream.toByteArray();
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}finally{
httpClient.getConnectionManager().shutdown();
}
return result;
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
progressDialog.show();
}
//更新ui
@Override
protected void onPostExecute(byte[] result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
Bitmap bitmap=BitmapFactory.decodeByteArray(result, 0,result.length);
imageView.setImageBitmap(bitmap);
progressDialog.dismiss();
}
@Override
protected void onProgressUpdate(Integer... values) {
// TODO Auto-generated method stub
super.onProgressUpdate(values);
progressDialog.setProgress(values[0]);
}
}
}
时间： 2024-08-06 16:06:21