怎样检查Android网络连接状态

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来源:互联网

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"?>
    <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
    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"?>
    <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。

    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。

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