添加项目文件。

testWPFDevelopers.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.8.34525.116
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "testWPFDevelopers", "testWPFDevelopers\testWPFDevelopers.csproj", "{0003FC75-7BBF-4BF1-B3A6-55D2D7C792DD}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{0003FC75-7BBF-4BF1-B3A6-55D2D7C792DD}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0003FC75-7BBF-4BF1-B3A6-55D2D7C792DD}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0003FC75-7BBF-4BF1-B3A6-55D2D7C792DD}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0003FC75-7BBF-4BF1-B3A6-55D2D7C792DD}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {78A48234-9673-425C-912D-1A983319881B}
+	EndGlobalSection
+EndGlobal

testWPFDevelopers/App.xaml

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+<Application x:Class="testWPFDevelopers.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:testWPFDevelopers"            
+             StartupUri="MainWindow.xaml">
+    <Application.Resources>
+       
+    </Application.Resources>
+</Application>

testWPFDevelopers/App.xaml.cs

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+using System.Configuration;
+using System.Data;
+using System.Windows;
+
+namespace testWPFDevelopers
+{
+    /// <summary>
+    /// Interaction logic for App.xaml
+    /// </summary>
+    public partial class App : Application
+    {
+    }
+
+}

testWPFDevelopers/AssemblyInfo.cs

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+using System.Windows;
+
+[assembly: ThemeInfo(
+    ResourceDictionaryLocation.None,            //where theme specific resource dictionaries are located
+                                                //(used if a resource is not found in the page,
+                                                // or application resource dictionaries)
+    ResourceDictionaryLocation.SourceAssembly   //where the generic resource dictionary is located
+                                                //(used if a resource is not found in the page,
+                                                // app, or any theme specific resource dictionaries)
+)]

testWPFDevelopers/MainViewModel.cs

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+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace testWPFDevelopers
+{
+    public class MainViewModel
+    {
+		private ObservableCollection<string> myVar;
+
+		public ObservableCollection<string> MyProperty
+		{
+			get { return myVar; }
+			set { myVar = value; }
+		}
+        public MainViewModel()
+        {
+              myVar = new ObservableCollection<string>();
+            myVar.Add("a001");
+            myVar.Add("保001");
+            myVar.Add("保德03");
+            myVar.Add("dc04");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+            myVar.Add("保德03");
+        }
+    }
+}

testWPFDevelopers/MainWindow.xaml

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+<Window x:Class="testWPFDevelopers.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        
+        xmlns:local="clr-namespace:testWPFDevelopers"
+        mc:Ignorable="d"
+        Title="MainWindow" Height="450" Width="800">
+    <Grid>
+        <ComboBox IsTextSearchEnabled="False"
+                  IsEditable="True"
+                  Height="30"
+                  HorizontalAlignment="Left"
+                  Margin="12,23,0,0"
+                  Name="comboBox1"
+                  VerticalAlignment="Top"
+                  Width="120"
+                  KeyUp="comboBox1_KeyUp" 
+                  MaxDropDownHeight="150"/>
+    </Grid>
+</Window>

testWPFDevelopers/MainWindow.xaml.cs

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+using System.Text;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Navigation;
+using System.Windows.Shapes;
+
+namespace testWPFDevelopers
+{
+    /// <summary>
+    /// Interaction logic for MainWindow.xaml
+    /// </summary>
+    public partial class MainWindow : Window
+    {
+        List<string> list = new List<string> { "aa", "bb", "abc", "csd", "sdlfks", "osdi", "awd" , "aa", "bb", "abc", "csd", "sdlfks", "osdi", "awd", "aa", "bb", "abc", "csd", "sdlfks", "osdi", "awd" };
+        public MainWindow()
+        {
+            InitializeComponent();
+            this.DataContext=new MainViewModel();
+            comboBox1.ItemsSource = list;
+        }
+        private void comboBox1_KeyUp(object sender, KeyEventArgs e)
+        {
+
+            List<string> mylist = new List<string>();
+            mylist = list.FindAll(delegate (string s) { return s.Contains(comboBox1.Text.Trim()); });
+            comboBox1.ItemsSource = mylist;
+            comboBox1.IsDropDownOpen = true;
+        }
+    }
+
+}

testWPFDevelopers/testWPFDevelopers.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net6.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <UseWPF>true</UseWPF>
+  </PropertyGroup>
+
+</Project>