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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<?xmlversion="1.0"encoding="utf-8"?>

<manifestxmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.detectinternetconnection"

    android:versionCode="1"

    android:versionName="1.0">

  

    <uses-sdkandroid:minSdkVersion="8"/>

  

    <application

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name">

        <activity

            android:name=".AndroidDetectInternetConnectionActivity"

            android:label="@string/app_name">

            <intent-filter>

                <actionandroid:name="android.intent.action.MAIN"/>

  

                <categoryandroid:name="android.intent.category.LAUNCHER"/>

            </intent-filter>

        </activity>

    </application>

  

    <!-- Internet Permissions -->

    <uses-permissionandroid:name="android.permission.INTERNET"/>

  

    <!-- Network State Permissions -->

    <uses-permissionandroid: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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packagecom.example.detectinternetconnection;

  

importandroid.content.Context;

importandroid.net.ConnectivityManager;

importandroid.net.NetworkInfo;

  

publicclass ConnectionDetector {

  

    privateContext _context;

  

    publicConnectionDetector(Context context){

        this._context = context;

    }

  

    publicboolean isConnectingToInternet(){

        ConnectivityManager connectivity = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);

          if(connectivity != null)

          {

              NetworkInfo[] info = connectivity.getAllNetworkInfo();

              if(info != null)

                  for(inti = 0; i < info.length; i++)

                      if(info[i].getState() == NetworkInfo.State.CONNECTED)

                      {

                          returntrue;

                      }

  

          }

          returnfalse;

    }

}

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 = newConnectionDetector(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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<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns: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" />

  

    <Buttonandroid: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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packagecom.example.detectinternetconnection;

  

importandroid.app.Activity;

importandroid.app.AlertDialog;

importandroid.content.Context;

importandroid.content.DialogInterface;

importandroid.os.Bundle;

importandroid.view.View;

importandroid.widget.Button;

  

publicclass AndroidDetectInternetConnectionActivity extendsActivity {

  

    // flag for Internet connection status

    Boolean isInternetPresent = false;

  

    // Connection detector class

    ConnectionDetector cd;

  

    @Override

    publicvoid onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

  

        Button btnStatus = (Button) findViewById(R.id.btn_check);

  

        // creating connection detector class instance

        cd = newConnectionDetector(getApplicationContext());

  

        /**

         * Check Internet status button click event

         * */

        btnStatus.setOnClickListener(newView.OnClickListener() {

  

            @Override

            publicvoid 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)

     * */

    publicvoid showAlertDialog(Context context, String title, String message, Boolean status) {

        AlertDialog alertDialog = newAlertDialog.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", newDialogInterface.OnClickListener() {

            publicvoid onClick(DialogInterface dialog, intwhich) {

            }

        });

  

        // 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。