用于判断软件打开时的网络连接状态，若无网络连接，提醒用户跳转到设置界面

    /** 
         * 设置在onStart()方法里面，可以在界面每次获得焦点的时候都进行检测 
         */  
          
        @Override  
        protected void onStart() {  
            ConnectivityManager manager = (ConnectivityManager) this  
                    .getSystemService(Context.CONNECTIVITY_SERVICE);  
            NetworkInfo info = manager.getActiveNetworkInfo();  
            if (info != null && info.isConnected()) {  
                Toast.makeText(MainActivity.this, "网络连接连接", 0).show();  
            } else {  
                AlertDialog.Builder builder = new Builder(MainActivity.this);  
                builder.setTitle("开启网络服务");  
                builder.setMessage("网络没有连接，请到设置进行网络设置！");  
                builder.setPositiveButton("确定",  
                        new DialogInterface.OnClickListener() {  
                            public void onClick(DialogInterface dialog, int which) {  
                                if (android.os.Build.VERSION.SDK_INT > 10) {  
                                    // 3.0以上打开设置界面，也可以直接用ACTION_WIRELESS_SETTINGS打开到wifi界面  
                                    startActivity(new Intent(  
                                            android.provider.Settings.ACTION_SETTINGS));  
                                } else {  
                                    startActivity(new Intent(  
                                            android.provider.Settings.ACTION_WIRELESS_SETTINGS));  
                                }  
                                dialog.cancel();  
                            }  
                        });  
      
                builder.setNegativeButton("取消",  
                        new DialogInterface.OnClickListener() {  
                            @Override  
                            public void onClick(DialogInterface dialog, int which) {  
                                dialog.cancel();  
                            }  
                        });  
                builder.show();  
            }  
            super.onStart();  
        }  

需要注册的权限  <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>