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
< ?xml version="1.0" encoding="utf-8"?>















3.创建一个新的类,名为ConnectionDetector.java,并输入以下代码。
ConnectionDetector.java
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。
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
< ?xml version="1.0" encoding="utf-8"?>




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。
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。
android internet connetion
android internet connetion