Android 判断有没有网

   **MainActivity   布局**
    <?xml version="1.0" encoding="utf-8"?>
    <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">
    
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button"
        tools:layout_editor_absoluteX="16dp"
        tools:layout_editor_absoluteY="16dp" />
    
    </android.support.constraint.ConstraintLayout>




**MainActivity 里面的代码**
 //第一步找控件
        Button button= findViewById(R.id.button);
        //第二步点击事件
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //第三步开启子线程
            new Thread(){
                @Override
                public void run() {
                    super.run();
                    //在这里写耗时操作(请求网络数据)
                    //第四步:判断网络状态
                    boolean networkConnected = Http.isNetworkConnected(MainActivity.this);
                    //判断有没有网
                    if (networkConnected){
                        //有网就请求数据
                        String get = Http.requestHttpGet("http://api.expoon.com/AppNews/getNewsList/type/1/p/1");
                        Gson gson=new Gson();
                        JsonBean bean = gon.fromJson(get, JsonBean.class);
                        //把数据传递给主线程
                        Message message=new Message();
                        message.what=0;
                        message.obj=bean;
                        handler.sendMessage(message);
                    }else{
                       handler.sendEmptyMessageDelayed(1,0);
                    }

                }
            }.start();

            }
        });

    }

    Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
        switch (msg.what){
            case 0:
                JsonBean bean= (JsonBean) msg.obj;
                Toast.makeText(MainActivity.this,""+bean.toString(),Toast.LENGTH_LONG).show();

                break;
            case 1:
                //没网就提示用户 没网
                Toast.makeText(MainActivity.this,"兄嘚,没网啊?",Toast.LENGTH_LONG).show();
                break;
        }
        }
    };








Http 类中的代码
public class Http {
    /**
     * 判断有没有网
     */
    public static boolean isNetworkConnected(Context context) {
        //注意要写网络权限
        //判断参数是否为空(必须)
        if (context != null) {
            //getSystemService 获取系统服务
            //获取连接管理器
            ConnectivityManager mConnectivityManager = (ConnectivityManager)
                    context.getSystemService(Context.CONNECTIVITY_SERVICE);
            //获取网络状态
            NetworkInfo info = mConnectivityManager.getActiveNetworkInfo();
            if (info != null) {
                //判断网络是否可用
                return info.isAvailable();
            }
        }
        return false;
    }


/**
     * 请求数据GET请求
     */
    public static String requestHttpGet(String strUrl) {
        try { //设置url
            URL url = new URL(strUrl);
            //获取HttpURLConnection
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            //设置为get请求
            connection.setRequestMethod("GET");
            //设置连接主机超时时间
            connection.setConnectTimeout(5000);
            //设置从主机读取数据超时
            connection.setReadTimeout(5000);
            //获取请求码（来判断网络请求是否正确）
            int code = connection.getResponseCode();
            //判断请求是否成功
            if (code == HttpURLConnection.HTTP_OK) {
                //如果数据请求成功
                //就获取数据
                InputStream stream = connection.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(stream, "utf-8"));
                //拼接字符串
                StringBuilder builder = new StringBuilder();
                //把数据读取从成字符串
                String str = "";
                while ((str = reader.readLine()) != null) {
                    //把一行行数据拼接成一行数据
                    builder.append(str);
                }
                //返回拼接后的数据
                return builder.toString();
            }
            //关闭连接
            connection.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}