android 判断网络连接是否可用

为了提高用户体验，我们在开发 android 应用的过程需要联网获取数据的时候我们首先要做的一步就是：

1.判断当前手机是否打开了网络，

2.打开了网络是否可以上网，

然后再去执行联网逻辑，避免没联网做不必要的工作！

通常情况下，我们是这样判断的

public static boolean isNetAvailable(Context context) {
ConnectivityManager connectManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);  
        return (connectManager.getActiveNetworkInfo() != null);
}

但是这样只完成了第一步，判断网络是否打开，

注意：打开并不代表就可以上网，

观察发现 NetworkInfo 有一个方法：

NetworkInfo.isAvailable()

官方的解释是

Indicates whether network connectivity is possible. A network is unavailable when a persistent or semi-persistent condition prevents the possibility of connecting to that network. Examples include 

The device is out of the coverage area for any network of this type. 
The device is on a network other than the home network (i.e., roaming), and data roaming has been disabled. 
The device's radio is turned off, e.g., because airplane mode is enabled. 
Returns:
true if the network is available, false otherwise

他列举了几种网络已连接但不可以上网的情况，

所以我们这样改改就好了：

public static boolean isNetAvailable(Context context) {
ConnectivityManager manager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);  
        NetworkInfo info = manager.getActiveNetworkInfo();
        return (info != null && info.isAvailable());
}