Question

怎么设置WPF的DatePicker默认显示“请选择一个日期”

Answer 1

可以,方法有2种,一种是用代码,一种是重写样式,我来演示一下用代码怎么实现

 //首先在你的App类,即创建项目的时候App.xaml下的类
 public partial class App : Application
    {
       //在启动方法中为时间控件注册一个加载事件
        void app_Startup(object sender,StartupEventArgs e)
        {
           
            EventManager.RegisterClassHandler(typeof(DatePicker),
            FrameworkElement.LoadedEvent,
            new RoutedEventHandler(DatePicker_Loaded));
        }
        void DatePicker_Loaded(object sender, RoutedEventArgs e)
        {
            var dp = sender as DatePicker;
            if (dp == null) return;
            
            var wm = RecursionFindControl<ContentControl>(dp, "PART_Watermark");
            if (wm == null) return;
            //重新默认水印值
            wm.Content = "请选择一个日期";
        }
     
        /// <summary>
        /// 递归寻找指定名称和指定类型的控件(辅助方法)
        /// </summary>
        /// <typeparam name="T">寻找的类型</typeparam>
        /// <param name="reference">对象</param>
        /// <param name="controlName">需要寻找的控件名称</param>
        /// <param name="maxLevel">最大递归级数</param>
        /// <param name="currentLevel">当前已经递归的级数</param>
        /// <returns>返回寻找的类型</returns>
        public static T RecursionFindControl<T>(DependencyObject reference, string controlName = "", int maxLevel = int.MaxValue, int currentLevel = 1) where T : class
        {
            DependencyObject obj = null;
            if (reference == null)
            {
                return obj as T;
            }
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(reference); i++)
            {
                obj = VisualTreeHelper.GetChild(reference, i);
                FrameworkElement elemnt = obj as FrameworkElement;
                if (elemnt == null)
                {
                    break;
                }

                if (elemnt is T &&
                    ((!string.IsNullOrEmpty(controlName)
                      && elemnt.Name == controlName)
                     || string.IsNullOrEmpty(controlName)))
                {
                    return obj as T;
                }
                else
                {
                    if (currentLevel < maxLevel)//递归层级限制
                    {
                        obj = RecursionFindControl<T>(obj, controlName, maxLevel, currentLevel + 1) as DependencyObject;
                        if (obj != null)
                        {
                            return obj as T;
                        }
                    }
                }
            }

            return obj as T;
        }
    }