AsyncTask 异步处理：
mainfest:
注意添加的：
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".Main2Activity"></activity>
</application>
代码 ：MainActivity.java
package com.example.wgscd.myapplication;
import android.graphics.BitmapFactory;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.graphics.Bitmap;
import android.os.AsyncTask;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import static android.R.attr.bitmap;
public class MainActivity extends AppCompatActivity {
Button btn1=null;
TextView txtView1=null;
ProgressBar progressBar;
int j=1;
String msg="";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn1=(Button) findViewById(R.id.btn1);
txtView1=(TextView)findViewById(R.id.textView1);
progressBar = (ProgressBar)findViewById(R.id.progressBar);
progressBar.setVisibility(View.INVISIBLE);
}
protected void btn1_Click(View view){
// txtView1.setText( j +"");
// j++;
downLoadPictue();
}
void downLoadPictue(){
DownImageTask asyncTask = new DownImageTask();
asyncTask.execute("http://www.xitongzijia.net/meinv/e/data/tmp/titlepic/pic43847d162a1452bfeb482be70d24bff9e5c99_200.jpg");
}
class DownImageTask extends AsyncTask<String, Integer, Bitmap> {
// 执行预处理
@Override
protected void onPreExecute() {
super.onPreExecute();
// 显示进度条
progressBar.setVisibility(View.VISIBLE);
progressBar.setMax(100);
}
// 后台进程的执行
@Override
protected Bitmap doInBackground(String... params) {
Bitmap bitmap=null;
try {
URL url = new URL(params[0]);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
// 进度条的更新，我这边只是用一个循环来示范，在实际应用中要使用已下载文件的大小和文件总大小的比例来更新
for (int i = 1; i <= 10; i++) {
publishProgress(i * 10);
Thread.sleep(200);
}
InputStream inputStream = conn.getInputStream();
bitmap = BitmapFactory.decodeStream(inputStream);
inputStream.close();
} catch (Exception e) {
e.printStackTrace();
msg= e.getMessage();
}
return bitmap;
}
// 运行于UI线程，对后台任务的结果做出处理，doInBackground方法执行的结果作为此方法的参数
@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
ImageView imageView = (ImageView) findViewById(R.id.imageView);
imageView.setImageBitmap(result);
progressBar.setVisibility(View.GONE);
}
// 运行于UI线程，如果在doInBackground(Params...)中使用了publishProgress(Progress...)，就会触发此方法
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
txtView1.setText( ""+ values[0] +"%" + msg);
progressBar.setProgress(values[0]);
}
}
}