Android：检查网络连接状态
（1）在AndroidManifest.xml文件中添加必要的权限。
访问网络我们需要 INTERNET 权限
检查网络状态我们需要 ACCESS_NETWORK_STATE 权限
<!-- Internet Permissions --> <uses-permission android:name="android.permission.INTERNET" /> <!-- Network State Permissions --> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
（2）创建工具类ConnectionDetector.java
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; } /** * 判断网络是否连接 * @return true/false */ 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; }}（3）上面工具类的使用：当需要在你的应用中检查网络状态时调用isConnectingToInternet()函数，返回true或false。
ConnectionDetector cd = new ConnectionDetector(getApplicationContext());Boolean isInternetPresent = cd.isConnectingToInternet(); // true or false
（4）下面是一个小测试，实现单击按钮，弹出alert dialog显示网络连接状态。
在res/layout/main.xml中创建一个按钮
<?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>
MainActivity.java
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(); }}（5）测试结果
Internet Connection
No Internet Connection
