开发笔记:Android中使用AsyncTask实现文件下载以及进度更新提示

1
2 <LinearLayout
3 xmlns:android="http://schemas.android.com/apk/res/android"
4 xmlns:tools="http://schemas.android.com/tools"
5 android:id="@+id/activity_main"
6 android:layout_
7 android:layout_
8 android:orientation="vertical"
9 tools:cOntext="com.example.administrator.asynctask.MainActivity">
10 <TextView
11 android:id="@+id/tv"
12 android:layout_
13 android:layout_
14 android:text="panhouye!"
15 android:textSize="20sp"/>
16 <ProgressBar
17 android:id="@+id/progress"
18 android:layout_
19 android:layout_
20
21 android:visibility="visible"/>
22 <Button
23 android:layout_
24 android:layout_
25 android:OnClick="image"
26 android:text="下载图片"/>
27

1 import android.os.AsyncTask;
2 import android.os.Environment;
3 import android.support.v7.app.AppCompatActivity;
4 import android.os.Bundle;
5 import android.view.View;
6 import android.widget.ProgressBar;
7 import android.widget.TextView;
8 import java.io.BufferedInputStream;
9 import java.io.BufferedOutputStream;
10 import java.io.File;
11 import java.io.FileOutputStream;
12 import java.net.HttpURLConnection;
13 import java.net.URL;
14 /**
15 * Created by panchengjia on 2016/12/19.
16 */
17 public class MainActivity extends AppCompatActivity {
18 //声明publishProgress的更新标记
19 private static final int PROGRESS_MAX = 0X1;
20 private static final int UPDATE = 0X2;
21 private TextView tv;
22 ProgressBar progress;
23 int contentLen;//声明要下载的文件总长
24 @Override
25 protected void onCreate(Bundle savedInstanceState) {
26 super.onCreate(savedInstanceState);
27 setContentView(R.layout.activity_main);
28 tv = (TextView) findViewById(R.id.tv);
29 progress = (ProgressBar) findViewById(R.id.progress);
30 }
31 public void image(View view){
32 //启用AsyncTask，传入需要执行的内容（图片地址）
33 new DownLoad().execute("http://cdnq.duitang.com/uploads/item/201402/22/20140222115440_jWNmx.thumb.700_0.jpeg");
34 }
35 class DownLoad extends AsyncTask{
36 //在执行实际的后台操作前被UI Thread调用
37 @Override
38 protected void onPreExecute() {
39 super.onPreExecute();
40 //准备下载前的初始进度
41 progress.setProgress(0);
42 }
43 //在onPreExecute执行，该方法运行在后台线程中
44 @Override
45 protected String doInBackground(String... params) {
46 try {
47 URL url = new URL(params[0]);
48 //获取连接
49 HttpURLConnection cOnnection= (HttpURLConnection) url.openConnection();
50 //获取下载文件的大小
51 cOntentLen= connection.getContentLength();
52 //根据下载文件大小设置进度条最大值（使用标记区别实时进度更新）
53 publishProgress(PROGRESS_MAX,contentLen);
54 //循环下载（边读取边存入）
55 BufferedInputStream bis = new BufferedInputStream(connection.getInputStream());
56 BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(new
57 File(Environment.getExternalStorageDirectory()+"/Download/ss.jpg")));
58 int len =-1;
59 byte[] bytes = new byte[1024];
60 while((len=bis.read(bytes))!=-1){
61 bos.write(bytes,0,len);
62 bos.flush();
63 //实时更新下载进度（使用标记区别最大值）
64 publishProgress(UPDATE,len);
65 //演示下载的图片太小，网速太快，休眠300毫秒，方便大家观察
66 Thread.sleep(300);
67 }
68 bos.close();
69 bis.close();
70 } catch (Exception e) {
71 e.printStackTrace();
72 }
73 return "下载完成";
74 }
75 //在publishProgress被调用后，UI thread会调用这个方法
76 @Override
77 protected void onProgressUpdate(Integer... values) {
78 super.onProgressUpdate(values);
79 switch (values[0]){
80 case PROGRESS_MAX:
81 progress.setMax(values[1]);
82 break;
83 case UPDATE:
84 progress.incrementProgressBy(values[1]);
85 //获取下载进度百分比并更新textview
86 int i=(progress.getProgress()*100)/contentLen;
87 tv.setText("下载进度为："+i+"%");
88 break;
89 }
90 }
91 //doInBackground方法执行完后被UI thread执行
92 @Override
93 protected void onPostExecute(String s) {
94 super.onPostExecute(s);
95 progress.setVisibility(View.GONE);
96 tv.setText(s);
97 }
98 }
99 }

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