android异步初级

在android中主线程（UI线程）不能执行耗时操作：时间比较长（ANR application no response )   、网络操作（直接抛异常）

因为android的主线程是不安全线程！！！！为了提高速度！！！主线程没有进行同步操作

三种主流解决方案：

1、异步操作

2、handle

3、Loader

两种非主流解决方案：

4、view.post(new ..)

5、runOnUiThread(new Runnable(){})

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异步任务：

异步： 三个泛型和四个步骤

     
同步：

异步任务下载一张图片的例子：

package com.example.myapplication;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity{

private ImageView imageView;
private EditText url;
private HttpURLConnection conn;

@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imageView = (ImageView) findViewById(R.id.imageview);
url = (EditText) findViewById(R.id.edittext);
}

public void go(View view){
final String urtStr = url.getText().toString();
MyTask task = new MyTask();
task.execute(urtStr);
}

public class MyTask extends AsyncTask<String, Integer, Bitmap>{

@Override
protected void onProgressUpdate(Integer... values){
Log.e("onProgressUpdate", Thread.currentThread().getName());
super.onProgressUpdate(values);
}

@Override
protected void onPreExecute(){
super.onPreExecute();
}

@Override
protected Bitmap doInBackground(String... params){
try{
String urtStr = params[0];
URL url = new URL(urtStr);
conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(10000);
conn.setReadTimeout(10000);
if(conn.getResponseCode() == HttpURLConnection.HTTP_OK){
InputStream is = conn.getInputStream();
Bitmap bitmap = BitmapFactory.decodeStream(is);
return bitmap;
}
}catch(Exception e){
e.printStackTrace();
}finally{
if(conn != null){
conn.disconnect();
}
}
return null;
}

@Override
protected void onPostExecute(Bitmap s){
if(s != null){
imageView.setImageBitmap(s);
}
super.onPostExecute(s);
}
}
}