怎样检查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

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<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="com.example.detectinternetconnection"     android:versionCode="1"     android:versionName="1.0" >        <uses-sdk android:minSdkVersion="8" />        <application         android:icon="@drawable/ic_launcher"         android:label="@string/app_name" >         <activity             android:name=".AndroidDetectInternetConnectionActivity"             android:label="@string/app_name" >             <intent-filter>                 <action android:name="android.intent.action.MAIN" />                    <category android:name="android.intent.category.LAUNCHER" />             </intent-filter>         </activity>     </application>        <!-- Internet Permissions -->     <uses-permission android:name="android.permission.INTERNET" />        <!-- Network State Permissions -->     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />    </manifest>

3.创建一个新的类，名为ConnectionDetector.java，并输入以下代码。

ConnectionDetector.java 

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package com.example.detectinternetconnection;    import android.content.Context; import android.net.ConnectivityManager; import android.net.NetworkInfo;    public class ConnectionDetector {        private Context _context;        public ConnectionDetector(Context context){         this._context = context;     }        public boolean isConnectingToInternet(){         ConnectivityManager connectivity = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);           if (connectivity != null)           {               NetworkInfo[] info = connectivity.getAllNetworkInfo();               if (info != null)                   for (int i = 0; i < info.length; i++)                       if (info[i].getState() == NetworkInfo.State.CONNECTED)                       {                           return true;                       }              }           return false;     } }

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。

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ConnectionDetector cd = new ConnectionDetector(getApplicationContext());    Boolean 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

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<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     android:orientation="vertical" >        <TextView         android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:text="Detect Internet Status" />        <Button android:id="@+id/btn_check"         android:layout_height="wrap_content"         android:layout_width="wrap_content"         android:text="Check Internet Status"         android:layout_centerInParent="true"/>    </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。

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package com.example.detectinternetconnection;    import android.app.Activity; import android.app.AlertDialog; import android.content.Context; import android.content.DialogInterface; import android.os.Bundle; import android.view.View; import android.widget.Button;    public class AndroidDetectInternetConnectionActivity extends Activity {        // flag for Internet connection status     Boolean isInternetPresent = false;        // Connection detector class     ConnectionDetector cd;        @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);            Button btnStatus = (Button) findViewById(R.id.btn_check);            // creating connection detector class instance         cd = new ConnectionDetector(getApplicationContext());            /**          * Check Internet status button click event          * */         btnStatus.setOnClickListener(new View.OnClickListener() {                @Override             public void onClick(View v) {                    // get Internet status                 isInternetPresent = cd.isConnectingToInternet();                    // check for Internet status                 if (isInternetPresent) {                     // Internet Connection is Present                     // make HTTP requests                     showAlertDialog(AndroidDetectInternetConnectionActivity.this, "Internet Connection",                             "You have internet connection", true);                 } else {                     // Internet connection is not present                     // Ask user to connect to Internet                     showAlertDialog(AndroidDetectInternetConnectionActivity.this, "No Internet Connection",                             "You don't have internet connection.", false);                 }             }            });        }        /**      * Function to display simple Alert Dialog      * @param context - application context      * @param title - alert dialog title      * @param message - alert message      * @param status - success/failure (used to set icon)      * */     public void showAlertDialog(Context context, String title, String message, Boolean status) {         AlertDialog alertDialog = new AlertDialog.Builder(context).create();            // Setting Dialog Title         alertDialog.setTitle(title);            // Setting Dialog Message         alertDialog.setMessage(message);            // Setting alert dialog icon         alertDialog.setIcon((status) ? R.drawable.success : R.drawable.fail);            // Setting OK Button         alertDialog.setButton("OK", new DialogInterface.OnClickListener() {             public void onClick(DialogInterface dialog, int which) {             }         });            // Showing Alert Message         alertDialog.show();     } }

运行并测试下你的程序吧！你将会得到类似下面的结果。