如何检查Android网络连接状态

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.xml

01<?xml version="1.0" encoding="utf-8"?>
02<manifest xmlns:android="http://schemas.android.com/apk/res/android"
03    package="com.example.detectinternetconnection"
04    android:versionCode="1"
05    android:versionName="1.0" >
06  
07    <uses-sdk android:minSdkVersion="8" />
08  
09    <application
10        android:icon="@drawable/ic_launcher"
11        android:label="@string/app_name" >
12        <activity
13            android:name=".AndroidDetectInternetConnectionActivity"
14            android:label="@string/app_name" >
15            <intent-filter>
16                <action android:name="android.intent.action.MAIN" />
17  
18                <category android:name="android.intent.category.LAUNCHER" />
19            </intent-filter>
20        </activity>
21    </application>
22  
23    <!-- Internet Permissions -->
24    <uses-permission android:name="android.permission.INTERNET" />
25  
26    <!-- Network State Permissions -->
27    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
28  
29</manifest>

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 = new ConnectionDetector(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.xml

01<?xml version="1.0" encoding="utf-8"?>
02<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
03    android:layout_width="fill_parent"
04    android:layout_height="fill_parent"
05    android:orientation="vertical" >
06  
07    <TextView
08        android:layout_width="fill_parent"
09        android:layout_height="wrap_content"
10        android:text="Detect Internet Status" />
11  
12    <Button android:id="@+id/btn_check"
13        android:layout_height="wrap_content"
14        android:layout_width="wrap_content"
15        android:text="Check Internet Status"
16        android:layout_centerInParent="true"/>
17  
18</RelativeLayout>

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 void showAlertDialog(Context context, String title, String message, Boolean status) {
66        AlertDialog alertDialog = new AlertDialog.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", new DialogInterface.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！你将会得到类似下面的结果。

原文链接