AIKKEY_WPFWin7/AIK.Behaviors/PlaceholderBehavior.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;

namespace AIK.Behaviors
{
    public static class PlaceholderBehavior
    {
        #region 依赖属性定义
        private static readonly DependencyPropertyKey IsPlaceholderActivePropertyKey =
            DependencyProperty.RegisterAttachedReadOnly(
                "IsPlaceholderActive",
                typeof(bool),
                typeof(PlaceholderBehavior),
                new PropertyMetadata(false));

        public static readonly DependencyProperty IsPlaceholderActiveProperty = IsPlaceholderActivePropertyKey.DependencyProperty;

        public static readonly DependencyProperty PlaceholderTextProperty =
            DependencyProperty.RegisterAttached(
                "PlaceholderText",
                typeof(string),
                typeof(PlaceholderBehavior),
                new PropertyMetadata(string.Empty, OnPlaceholderTextChanged));

        // 添加一个属性来存储原始绑定
        private static readonly DependencyProperty OriginalBindingProperty =
            DependencyProperty.RegisterAttached(
                "OriginalBinding",
                typeof(Binding),
                typeof(PlaceholderBehavior));

        // 添加一个属性来标记是否正在设置Placeholder
        private static readonly DependencyProperty IsSettingPlaceholderProperty =
            DependencyProperty.RegisterAttached(
                "IsSettingPlaceholder",
                typeof(bool),
                typeof(PlaceholderBehavior),
                new PropertyMetadata(false));
        #endregion

        #region 公共方法
        public static bool GetIsPlaceholderActive(DependencyObject obj)
        {
            return (bool)obj.GetValue(IsPlaceholderActiveProperty);
        }

        public static string GetPlaceholderText(DependencyObject obj)
        {
            return (string)obj.GetValue(PlaceholderTextProperty);
        }

        public static void SetPlaceholderText(DependencyObject obj, string value)
        {
            obj.SetValue(PlaceholderTextProperty, value);
        }
        #endregion

        #region 私有方法
        private static bool GetIsSettingPlaceholder(DependencyObject obj)
        {
            return (bool)obj.GetValue(IsSettingPlaceholderProperty);
        }

        private static void SetIsSettingPlaceholder(DependencyObject obj, bool value)
        {
            obj.SetValue(IsSettingPlaceholderProperty, value);
        }

        private static Binding GetOriginalBinding(DependencyObject obj)
        {
            return (Binding)obj.GetValue(OriginalBindingProperty);
        }

        private static void SetOriginalBinding(DependencyObject obj, Binding value)
        {
            obj.SetValue(OriginalBindingProperty, value);
        }
        #endregion

        #region 事件处理
        private static void OnPlaceholderTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is TextBox textBox)
            {
                // 确保只注册一次事件
                textBox.Loaded -= OnTextBoxLoaded;
                textBox.GotFocus -= OnTextBoxGotFocus;
                textBox.LostFocus -= OnTextBoxLostFocus;
                textBox.TextChanged -= OnTextBoxTextChanged;

                textBox.Loaded += OnTextBoxLoaded;
                textBox.GotFocus += OnTextBoxGotFocus;
                textBox.LostFocus += OnTextBoxLostFocus;
                textBox.TextChanged += OnTextBoxTextChanged;

                // 保存原始绑定
                var binding = BindingOperations.GetBinding(textBox, TextBox.TextProperty);
                if (binding != null)
                {
                    SetOriginalBinding(textBox, binding);
                }

                // 如果已经加载，立即初始化
                if (textBox.IsLoaded)
                {
                    InitializePlaceholder(textBox);
                }
            }
        }

        private static void OnTextBoxLoaded(object sender, RoutedEventArgs e)
        {
            InitializePlaceholder((TextBox)sender);
        }

        private static void OnTextBoxGotFocus(object sender, RoutedEventArgs e)
        {
            var textBox = (TextBox)sender;
            if (GetIsPlaceholderActive(textBox))
            {
                // 标记开始设置Placeholder，避免触发数据源更新
                SetIsSettingPlaceholder(textBox, true);

                // 移除placeholder
                textBox.Text = string.Empty;
                textBox.SetValue(IsPlaceholderActivePropertyKey, false);
                textBox.Foreground = Brushes.Black;

                // 恢复数据绑定
                RestoreBinding(textBox);

                SetIsSettingPlaceholder(textBox, false);
            }
        }

        private static void OnTextBoxLostFocus(object sender, RoutedEventArgs e)
        {
            var textBox = (TextBox)sender;
            if (string.IsNullOrEmpty(textBox.Text))
            {
                ShowPlaceholder(textBox);
            }
        }

        private static void OnTextBoxTextChanged(object sender, TextChangedEventArgs e)
        {
            var textBox = (TextBox)sender;

            // 如果正在设置Placeholder，不处理TextChanged事件
            if (GetIsSettingPlaceholder(textBox))
                return;

            // 只有在不是placeholder状态时才处理
            if (!GetIsPlaceholderActive(textBox))
            {
                // 如果文本变为空，显示placeholder
                if (string.IsNullOrEmpty(textBox.Text) && !textBox.IsFocused)
                {
                    ShowPlaceholder(textBox);
                }
                else
                {
                    // 正常文本变化，确保数据绑定是激活的
                    EnsureBindingActive(textBox);
                }
            }
        }
        #endregion

        #region 核心方法
        private static void InitializePlaceholder(TextBox textBox)
        {
            // 检查当前文本是否为空或者就是Placeholder文本
            var currentText = textBox.Text;
            var placeholderText = GetPlaceholderText(textBox);

            if (string.IsNullOrEmpty(currentText) || currentText == placeholderText)
            {
                ShowPlaceholder(textBox);
            }
        }

        private static void ShowPlaceholder(TextBox textBox)
        {
            var placeholderText = GetPlaceholderText(textBox);
            if (!string.IsNullOrEmpty(placeholderText))
            {
                // 标记开始设置Placeholder
                SetIsSettingPlaceholder(textBox, true);

                // 临时解除数据绑定，避免触发数据源更新
                SuspendBinding(textBox);

                // 设置Placeholder文本
                textBox.Text = placeholderText;
                textBox.SetValue(IsPlaceholderActivePropertyKey, true);
                textBox.Foreground = new SolidColorBrush(Color.FromArgb(0xFF, 0xA0, 0xAE, 0xC0));

                SetIsSettingPlaceholder(textBox, false);
            }
        }

        // 临时解除数据绑定
        private static void SuspendBinding(TextBox textBox)
        {
            // 清除绑定，但保留绑定表达式
            var bindingExpression = textBox.GetBindingExpression(TextBox.TextProperty);
            if (bindingExpression != null)
            {
                // 保存原始绑定（如果还没有保存的话）
                if (GetOriginalBinding(textBox) == null)
                {
                    var binding = BindingOperations.GetBinding(textBox, TextBox.TextProperty);
                    SetOriginalBinding(textBox, binding);
                }

                // 清除绑定，这样设置文本就不会更新数据源
                BindingOperations.ClearBinding(textBox, TextBox.TextProperty);
            }
        }

        // 恢复数据绑定
        private static void RestoreBinding(TextBox textBox)
        {
            var originalBinding = GetOriginalBinding(textBox);
            if (originalBinding != null)
            {
                // 恢复原始绑定
                textBox.SetBinding(TextBox.TextProperty, originalBinding);

                // 立即更新数据源为空值
                var bindingExpression = textBox.GetBindingExpression(TextBox.TextProperty);
                bindingExpression?.UpdateSource();
            }
        }

        // 确保数据绑定是激活的
        private static void EnsureBindingActive(TextBox textBox)
        {
            var currentBinding = BindingOperations.GetBinding(textBox, TextBox.TextProperty);
            var originalBinding = GetOriginalBinding(textBox);

            // 如果没有当前绑定但有原始绑定，恢复绑定
            if (currentBinding == null && originalBinding != null)
            {
                textBox.SetBinding(TextBox.TextProperty, originalBinding);
            }
        }
        #endregion
    }
}