ShrlAlgoToolkit/Melskin/Controls/SearchableComboBox.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace Melskin.Controls
{
    /// <summary>
    /// 搜索过滤的下拉框控件
    /// 自定义了ItemTemplate的时候，SearchableComboBox 设置 TextSearch.TextPath 附加属性,这个属性告诉 ComboBox：“虽然我的下拉列表长得很复杂（有颜色、有图标），但当你需要把我当成‘文本’处理（比如显示在输入框里、或者搜索时），请使用这个属性”
    /// </summary>
    public class SearchableComboBox : ComboBox
    {
        private TextBox _editableTextBox;
        private bool _isInternalOperation;

        static SearchableComboBox()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(SearchableComboBox), new FrameworkPropertyMetadata(typeof(SearchableComboBox)));
        }

        public SearchableComboBox()
        {
            IsEditable = true;
            IsTextSearchEnabled = false;
            StaysOpenOnEdit = true;
        }

        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
            if (GetTemplateChild("PART_EditableTextBox") is TextBox _editableTextBox)
            {
                _editableTextBox.TextChanged += OnEditableTextBoxTextChanged;
                // 点击时全选
                _editableTextBox.GotFocus += (s, e) => _editableTextBox.SelectAll();
            }
        }

        protected override void OnSelectionChanged(SelectionChangedEventArgs e)
        {
            if (_isInternalOperation) return;

            _isInternalOperation = true;
            base.OnSelectionChanged(e);

            // 重点 1：选中项改变后，必须彻底清空过滤器，否则下次打开下拉框只剩下一项
            this.Items.Filter = null;
            _isInternalOperation = false;
        }

        private void OnEditableTextBoxTextChanged(object sender, TextChangedEventArgs e)
        {
            if (_isInternalOperation) return;

            string searchText = _editableTextBox.Text;
            string selectedText = GetItemDisplayText(SelectedItem);

            // 重点 2：断开锁定逻辑
            // 如果文本框的内容和当前选中项的文本不一致，说明用户正在打字替换内容
            if (SelectedItem != null && searchText != selectedText)
            {
                _isInternalOperation = true;
                SelectedItem = null; // 必须将 SelectedItem 设为 null，否则 WPF 会强行还原文本
                _isInternalOperation = false;
            }

            // 重点 3：执行过滤
            this.Items.Filter = item =>
            {
                if (string.IsNullOrEmpty(searchText)) return true;

                string itemText = GetItemDisplayText(item);

                // 只要包含关键字就显示（忽略大小写）
                return itemText.IndexOf(searchText, StringComparison.OrdinalIgnoreCase) >= 0;
            };

            // 自动打开下拉框
            if (!IsDropDownOpen && _editableTextBox.IsFocused && !string.IsNullOrEmpty(searchText))
            {
                IsDropDownOpen = true;
            }
        }

        private string GetItemDisplayText(object item)
        {
            if (item == null) return string.Empty;
            if (item is ComboBoxItem cbi) return cbi.Content?.ToString() ?? string.Empty;

            // 兼容 DisplayMemberPath 或 TextSearch.TextPath
            string path = DisplayMemberPath;
            if (string.IsNullOrEmpty(path)) path = TextSearch.GetTextPath(this);

            if (!string.IsNullOrEmpty(path))
            {
                var prop = item.GetType().GetProperty(path);
                if (prop != null) return prop.GetValue(item)?.ToString() ?? string.Empty;
            }
            return item.ToString()!;
        }
    }
}