public boolean isOnline() {
    ConnectivityManager cm =
        (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo netInfo = cm.getActiveNetworkInfo();
    return netInfo != null && netInfo.isConnectedOrConnecting();
}
在AndroidManifest.xml中添加下面权限:
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
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