Android 使用AsyncTask 下载图片的例子,学会使用AsyncTask
1.添加布局文件：activity_main.xml
1 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 2 xmlns:tools="http://schemas.android.com/tools" 3 android:layout_width="match_parent" 4 android:layout_height="match_parent" 5 android:orientation="vertical" > 6 7 <ImageView 8 android:id="@+id/mImageView" 9 android:layout_width="300dp" 10 android:layout_height="300dp" /> 11 12 <ProgressBar 13 android:id="@+id/mProgressBar" 14 style="?android:attr/progressBarStyleHorizontal" 15 android:layout_width="fill_parent" 16 android:layout_height="wrap_content" 17 android:maxHeight="10dip" 18 android:minHeight="10dip" /> 19 20 <Button 21 android:id="@+id/btnGetImg" 22 android:layout_width="120dp" 23 android:layout_height="50dp" 24 android:text="Getmage" /> 25 26 <Button 27 android:id="@+id/btnAbort" 28 android:layout_width="120dp" 29 android:layout_height="50dp" 30 android:text="Abort" /> 31 32 </LinearLayout>
2.添加java文件MainActivity.java
1 package com.example.loadimgfrominternet;
2
3 import java.io.IOException;
4 import java.io.InputStream;
5 import java.io.OutputStream;
6 import java.net.HttpURLConnection;
7 import java.net.MalformedURLException;
8 import java.net.URL;
9 import java.net.URLConnection;
10
11 import android.app.Activity;
12 import android.content.Context;
13 import android.graphics.Bitmap;
14 import android.graphics.BitmapFactory;
15 import android.os.AsyncTask;
16 import android.os.Bundle;
17 import android.os.SystemClock;
18 import android.view.View;
19 import android.view.View.OnClickListener;
20 import android.widget.Button;
21 import android.widget.ImageView;
22 import android.widget.ProgressBar;
23
24 public class MainActivity extends Activity implements OnClickListener {
25
26 private Button btnGetImg;
27 private Button btnAbort;
28 private ProgressBar mProgressBar;
29 private ImageView mImageView;
30 private static final String ImageUrl = "//images0.cnblogs.com/i/169207/201408/112229149526951.png";
31
32 ImageLoader loader = null;
33
34 @Override
35 protected void onCreate(Bundle savedInstanceState) {
36 super.onCreate(savedInstanceState);
37 setContentView(R.layout.activity_main);
38 initView();
39 }
40
41 private void initView() {
42 btnGetImg = (Button) findViewById(R.id.btnGetImg);
43 btnAbort = (Button) findViewById(R.id.btnAbort);
44 mProgressBar = (ProgressBar) findViewById(R.id.mProgressBar);
45 btnGetImg.setOnClickListener(this);
46 btnAbort.setOnClickListener(this);
47
48 mProgressBar.setVisibility(View.INVISIBLE);
49 mImageView = (ImageView) findViewById(R.id.mImageView);
50 }
51
52 @Override
53 public void onClick(View v) {
54 int id = v.getId();
55 if (id == R.id.btnGetImg) {
56 loader = new ImageLoader();
57 loader.execute(ImageUrl);
58 btnGetImg.setEnabled(false);
59 } else if (id == R.id.btnAbort) {
60 loader.cancel(true);
61 btnGetImg.setEnabled(true);
62 }
63 }
64
65 class ImageLoader extends AsyncTask<String, Integer, Bitmap> {
66 @Override
67 protected void onPreExecute() {
68 mProgressBar.setVisibility(View.VISIBLE);
69 mProgressBar.setProgress(0);
70 mImageView.setImageResource(R.drawable.noimg);
71 super.onPreExecute();
72 }
73
74 @Override
75 protected Bitmap doInBackground(String... params) {
76 String imgUri = params[0];
77
78 try {
79 URL url = null;
80 HttpURLConnection conn = null;
81 InputStream inputStream = null;
82 OutputStream outputStream = null;
83 String filename = "local_temp_image";
84
85 try {
86
87 url = new URL(imgUri);
88 conn = (HttpURLConnection) url.openConnection();
89 conn.setDoInput(true);
90 conn.setDoOutput(false);
91 conn.setConnectTimeout(20 * 1000);
92 inputStream = conn.getInputStream();
93 outputStream = openFileOutput(filename,
94 Context.MODE_PRIVATE);
95 byte[] data = new byte[1024];
96 int seg = 0;
97 long total = conn.getContentLength();
98 long current = 0;
99 while (!isCancelled()
100 && (seg = inputStream.read(data)) != -1) {
101 outputStream.write(data, 0, seg);
102 current += seg;
103 int progress = (int) ((float) current / total * 100);
104 publishProgress(progress);// // 通知进度条UI更新
105 SystemClock.sleep(1000);
106 }
107 } finally {
108 if (conn != null) {
109 conn.disconnect();
110 }
111 if (inputStream != null) {
112 inputStream.close();
113 }
114 if (outputStream != null) {
115 outputStream.close();
116 }
117 }
118 // return BitmapFactory.decodeStream(HandlerData(ImageUrl));
119 return BitmapFactory.decodeFile(getFileStreamPath(filename)
120 .getAbsolutePath());
121 } catch (MalformedURLException e) {
122 e.printStackTrace();
123 } catch (IOException e) {
124 e.printStackTrace();
125 }
126 return null;
127 }
128
129 @Override
130 protected void onProgressUpdate(Integer... values) {
131 if (isCancelled())
132 return;
133 mProgressBar.setProgress(values[0]);
134 btnGetImg.setText(values[0] + "%");
135 super.onProgressUpdate(values);
136 }
137
138 @Override
139 protected void onPostExecute(Bitmap bitmap) {
140 if (bitmap != null) {
141 mImageView.setImageBitmap(bitmap);
142 }
143 mProgressBar.setVisibility(View.INVISIBLE);
144 mProgressBar.setProgress(0);
145 btnAbort.setEnabled(false);
146 super.onPostExecute(bitmap);
147 }
148 }
149
150 /* 根据URI地址读取输入流 */
151 public static InputStream HandlerData(String url) {
152 InputStream inStream = null;
153
154 try {
155 URL feedUrl = new URL(url);
156 URLConnection conn = feedUrl.openConnection();
157 conn.setConnectTimeout(10 * 1000);
158 inStream = conn.getInputStream();
159 } catch (Exception e) {
160 e.printStackTrace();
161 }
162
163 return inStream;
164 }
165 }
