怎样检查Android网络连接状态

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<?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>

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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;

    }

}

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ConnectionDetector
cd = new

ConnectionDetector(getApplicationContext());

Boolean
isInternetPresent = cd.isConnectingToInternet(); //
true or false

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<?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>

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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();

    }

}