alertController通过点语法添加action和textField， 具体实现：
HGAlertViewController * alertVC = [HGAlertViewController alertControllerWithTitle:@"提示" message:@"选择" preferredStyle:(UIAlertControllerStyleAlert)];
alertVC.addInput(@"输入账号",^(UITextField *textField){
[[textField rac_textSignal] subscribeNext:^(id x) {
NSLog(@"%@",textField.text);
}];
}).addAction(@"取消",^(UIAlertAction * action){
NSLog(@"取消");
}).addAction(@"确定",^(UIAlertAction *action){
NSLog(@"确定");
});
[self presentViewController:alertVC animated:true completion:nil];