Android——检查网络是否已经链接

新建一个项目testNet

添加一个button

　　layout.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context="com.example.testnet.MainActivity" ><TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="@string/hello_world" /><Buttonandroid:id="@+id/testNetwrkBtn"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_below="@+id/textView1"android:layout_centerHorizontal="true"android:layout_marginTop="31dp"android:text="@string/btn_testNet" />
</RelativeLayout>

新建一个外部类，实现接口OnClickListener

Btn1Listener.java：

package com.example.testnet;import android.app.Activity;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.TextView;
import android.widget.Toast;public class Btn1Listener implements OnClickListener {private Context context;private TextView tv1;private ConnectivityManager cm;public Btn1Listener(Context context) {this.context = context;}@Overridepublic void onClick(View v) {//把上下文对象转型为ActivityActivity c = ((Activity) context);//获取文本控件tv1 = (TextView) c.findViewById(R.id.textView1);
//        tv1.setBackgroundColor(0);try{//获取网络。。。。cm = (ConnectivityManager) c.getSystemService(c.CONNECTIVITY_SERVICE);NetworkInfo info = cm.getActiveNetworkInfo();if(info == null){//提示没有网络
                tv1.setText(R.string.text_Net1);tv1.setBackgroundResource(R.color.red);}else{tv1.setText(R.string.text_Net0);tv1.setBackgroundResource(R.color.green);//不需要提示，继续执行相关的代码
            }}catch(RuntimeException e){//用户没授权的时候给出提示（由于不知道怎么提示用户授权，只能用Toast了，怪我小白）Toast.makeText(c, "没有权限，请授权", Toast.LENGTH_SHORT).show();}}}

然后在Activity类给button绑定点击事件

package com.example.testnet;import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;public class MainActivity extends Activity {private Button btn1;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);btn1 = (Button) findViewById(R.id.testNetwrkBtn);btn1.setOnClickListener(new Btn1Listener(this));}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);return true;}@Overridepublic boolean onOptionsItemSelected(MenuItem item) {// Handle action bar item clicks here. The action bar will// automatically handle clicks on the Home/Up button, so long// as you specify a parent activity in AndroidManifest.xml.int id = item.getItemId();if (id == R.id.action_settings) {return true;}return super.onOptionsItemSelected(item);}
}

注意：检查网络链接需要在AndroidManifest.xml中授予相关权限

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.example.testnet"android:versionCode="1"android:versionName="1.0" ><!-- 授予局域网权限 --><uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"  /><!-- 授予互联网权限 --><uses-permission android:name="android.permission.INTERNET"/><uses-sdkandroid:minSdkVersion="17"android:targetSdkVersion="20" /><applicationandroid:allowBackup="true"android:icon="@drawable/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme" ><activityandroid:name=".MainActivity"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></manifest>