网络判断

主方法

public class MainActivity extends AppCompatActivity {    private ConnectivityManager con;       private ListView lv;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        lv = (ListView) findViewById(R.id.lv);        con = (ConnectivityManager) this.getSystemService(CONNECTIVITY_SERVICE);        NetworkInfo networkInfo = con.getActiveNetworkInfo();        int type = networkInfo.getType();        if (networkInfo!=null&&networkInfo.isAvailable()){            Toast.makeText(this,"网络可用",Toast.LENGTH_LONG).show();               }else{            Toast.makeText(this,"网络不可用",Toast.LENGTH_LONG).show();            new AlertDialog.Builder(MainActivity.this)            .setTitle("网络")                    .setMessage("网络未连接，是否去设置")                    .setPositiveButton("确定", new DialogInterface.OnClickListener() {                        @Override                        public void onClick(DialogInterface dialog, int which) {                            startActivity(new Intent(Settings.ACTION_WIFI_SETTINGS));                        }                    })                    .setNegativeButton("取消",null)                    .show();        }    }}