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
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | <? 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
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | 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。
| 1 2 3 | 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
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | <? 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。
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 | 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。
