在发送任何HTTP请求前最好检查下网络连接状态，这样可以避免异常。这个教程将会介绍怎样在你的应用中检测网络连接状态。
创建新的项目
1.在Eclipse IDE中创建一个新的项目并把填入必须的信息。 File->New->Android Project
2.创建新项目后的第一步是要在AndroidManifest.xml文件中添加必要的权限。
为了访问网络我们需要 INTERNET 权限
为了检查网络状态我们需要 ACCESS_NETWORK_STATE 权限
AndroidManifest.xml01
02
03 package="com.example.detectinternetconnection"
04 android:versionCode="1"
05 android:versionName="1.0" >
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10 android:icon="@drawable/ic_launcher"
11 android:label="@string/app_name" >
12
13 android:name=".AndroidDetectInternetConnectionActivity"
14 android:label="@string/app_name" >
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3.创建一个新的类，名为ConnectionDetector.java，并输入以下代码。
ConnectionDetector.java
01package com.example.detectinternetconnection;
02
03import android.content.Context;
04import android.net.ConnectivityManager;
05import android.net.NetworkInfo;
06
07public class ConnectionDetector {
08
09 private Context _context;
10
11 public ConnectionDetector(Context context){
12 this._context = context;
13 }
14
15 public boolean isConnectingToInternet(){
16 ConnectivityManager connectivity = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);
17 if (connectivity != null)
18 {
19 NetworkInfo[] info = connectivity.getAllNetworkInfo();
20 if (info != null)
21 for (int i = 0; i < info.length; i++)
22 if(info[i].getState() == NetworkInfo.State.CONNECTED)
23 {
24 return true;
25 }
26
27 }
28 return false;
29 }
30}
4.当你需要在你的应用中检查网络状态时调用isConnectingToInternet()函数，它会返回true或false。1ConnectionDetector cd = newConnectionDetector(getApplicationContext());
2
3Boolean isInternetPresent = cd.isConnectingToInternet(); // true or false
5.在这个教程中为了测试我仅仅简单的放置了一个按钮。只要按下这个按钮就会弹出一个 alert dialog 显示网络连接状态。
6.打开 res/layout 目录下的 main.xml 并创建一个按钮。
main.xml01
02
03 android:layout_width="fill_parent"
04 android:layout_height="fill_parent"
05 android:orientation="vertical" >
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07
08 android:layout_width="fill_parent"
09 android:layout_height="wrap_content"
10 android:text="Detect Internet Status" />
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1213 android:layout_height="wrap_content"
14 android:layout_width="wrap_content"
15 android:text="Check Internet Status"
16 android:layout_centerInParent="true"/>
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7.最后打开你的 MainActivity 文件并粘贴下面的代码。在下面的代码中我用一个 alert dialog 来显示预期的状态信息。01package com.example.detectinternetconnection;
02
03import android.app.Activity;
04import android.app.AlertDialog;
05import android.content.Context;
06import android.content.DialogInterface;
07import android.os.Bundle;
08import android.view.View;
09import android.widget.Button;
10
11public class AndroidDetectInternetConnectionActivity extends Activity {
12
13 // flag for Internet connection status
14 Boolean isInternetPresent = false;
15
16 // Connection detector class
17 ConnectionDetector cd;
18
19 @Override
20 public void onCreate(Bundle savedInstanceState) {
21 super.onCreate(savedInstanceState);
22 setContentView(R.layout.main);
23
24 Button btnStatus = (Button) findViewById(R.id.btn_check);
25
26 // creating connection detector class instance
27 cd = new ConnectionDetector(getApplicationContext());
28
29 /**
30 * Check Internet status button click event
31 * */
32 btnStatus.setOnClickListener(new View.OnClickListener() {
33
34 @Override
35 public void onClick(View v) {
36
37 // get Internet status
38 isInternetPresent = cd.isConnectingToInternet();
39
40 // check for Internet status
41 if (isInternetPresent) {
42 // Internet Connection is Present
43 // make HTTP requests
44 showAlertDialog(AndroidDetectInternetConnectionActivity.this, "Internet Connection",
45 "You have internet connection", true);
46 } else {
47 // Internet connection is not present
48 // Ask user to connect to Internet
49 showAlertDialog(AndroidDetectInternetConnectionActivity.this, "No Internet Connection",
50 "You don't have internet connection.", false);
51 }
52 }
53
54 });
55
56 }
57
58 /**
59 * Function to display simple Alert Dialog
60 * @param context - application context
61 * @param title - alert dialog title
62 * @param message - alert message
63 * @param status - success/failure (used to set icon)
64 * */
65 public voidshowAlertDialog(Context context, String title, String message, Boolean status) {
66 AlertDialog alertDialog = newAlertDialog.Builder(context).create();
67
68 // Setting Dialog Title
69 alertDialog.setTitle(title);
70
71 // Setting Dialog Message
72 alertDialog.setMessage(message);
73
74 // Setting alert dialog icon
75 alertDialog.setIcon((status) ? R.drawable.success : R.drawable.fail);
76
77 // Setting OK Button
78 alertDialog.setButton("OK", newDialogInterface.OnClickListener() {
79 public void onClick(DialogInterface dialog, int which) {
80 }
81 });
82
83 // Showing Alert Message
84 alertDialog.show();
85 }
86}
运行并测试下你的程序吧!
