展开时重绘组合框项目

Question

我有一个带有绑定组合框的 .net 3.5 Windows 应用程序。 我已经重写了 DrawItem 事件，以根据某些条件为各个项目的背景着色。 我运行异步线程，它更新条件值并调用 Invalidate() 来重绘组合框。

这一切都运行得很好，除非组合框展开时 - 仅针对列表中突出显示的项目调用 DrawItem。 其他项目仅在用户执行某些操作时刷新，例如将鼠标悬停在列表中的另一个项目上或单击不同的控件。 我希望其他项目在列表打开时自动重绘。 我怎样才能做到这一点？ 是否可以？

谢谢

编辑：我确定扩展列表中突出显示的任何项目都会在主组合框显示中重新绘制。 列表中的任何项目都不会在控件的展开部分中重新绘制。

编辑：这是一个精简的示例表单。 对于任何想要测试的人，您应该能够创建一个新的 Windows 窗体应用程序并将其添加到新的类文件中，并且它应该构建。

要重现该行为，请单击“检测”按钮，然后打开组合框并将鼠标悬停在 COM1 上。 测试结果将按照1、3、2的顺序完成。 您可以看到，当组合框打开时，COM3 保持黄色，直到您将突出显示移到它上面然后关闭。

using System;
using System.Windows.Forms;
using System.Collections.Generic;
using System.IO.Ports;
using System.Diagnostics;
using System.Drawing;

namespace combocolor
{
public partial class Demo2 : Form
{
private System.ComponentModel.IContainer components = null;
private System.Windows.Forms.Label ComPortLabel;
private System.Windows.Forms.ComboBox ComPortComboBox;
private System.Windows.Forms.ErrorProvider MainErrorProvider;
private System.Windows.Forms.Button autoQueryButton;

delegate PortTestResult TestPortDelegate(string portName);
delegate void UpdateTestResultsDelegate(PortTestResult portTestResult);

string[] _ports = new string[] { "COM1", "COM2", "COM3" };
Dictionary<string, int> _autoDetectResults = null;

public Demo2()
{
    InitializeComponent();
}

private void Settings_Load(object sender, EventArgs e)
{
    this.ComPortComboBox.Items.AddRange(this._ports);
    this.ComPortComboBox.SelectedIndex = 0;
}

private void autoQueryButton_Click(object sender, EventArgs e)
{
    // start port testing
    this._autoDetectResults = new Dictionary<string, int>(this._ports.Length);
    foreach (string portName in this._ports)
    {
        this._autoDetectResults.Add(portName, 0);
        this.ComPortComboBox.Invalidate();

        try
        {
            TestPortDelegate testDel = new TestPortDelegate(TestSerialPort);    // check port on a new thread
            testDel.BeginInvoke(portName, new AsyncCallback(TestFinishedCallback), testDel);
        }
        catch (Exception ex)
        {
            System.Diagnostics.Debug.WriteLine(ex);
        }
    }
}

private void ComPortComboBox_DrawItem(object sender, DrawItemEventArgs e)
{
    SolidBrush backgroundBrush, foregroundBrush;
    Dictionary<int, Color> colormap = new Dictionary<int, Color>();

    colormap.Add(0, Color.Yellow);
    colormap.Add(-1, Color.Red);
    colormap.Add(1, Color.LimeGreen);
    string itemText = (string)ComPortComboBox.Items[e.Index];

    // select a background color based on autodetect status
    if (this._autoDetectResults == null)
    {
        backgroundBrush = new System.Drawing.SolidBrush(e.BackColor);
    }
    else
    {
        int key = this._autoDetectResults[itemText];
        backgroundBrush = new SolidBrush(colormap[key]);
    }

    if ((e.State & DrawItemState.Selected) > 0 && (e.State & DrawItemState.ComboBoxEdit) == 0)
    {
        e.DrawBackground(); // draws the blue highlight
        foregroundBrush = new SolidBrush(e.ForeColor); // text color
    }
    else
    {
        e.Graphics.FillRectangle(backgroundBrush, e.Bounds); // draws the color based on the autodetect results
        foregroundBrush = new SolidBrush(this.ComPortComboBox.ForeColor); // text color 
    }

    e.Graphics.DrawString(itemText, e.Font, foregroundBrush, e.Bounds); // draw the text
}

private PortTestResult TestSerialPort(string portName)
{
    PortTestResult result = new PortTestResult();
    result.PortName = portName;

    // simulated results
    switch (portName)
    {
        case "COM1":
            System.Threading.Thread.Sleep(2000);
            result.UseThisPort = false;
            break;
        case "COM2":
            System.Threading.Thread.Sleep(6000);
            result.UseThisPort = true;
            break;
        case "COM3":
            System.Threading.Thread.Sleep(4000);
            result.UseThisPort = false;
            break;
    }

    return result;
}

private void TestFinishedCallback(IAsyncResult ar)
{
    // get the results from the test function
    TestPortDelegate testPortDelegate = (TestPortDelegate)((System.Runtime.Remoting.Messaging.AsyncResult)ar).AsyncDelegate;
    PortTestResult portTestResult = testPortDelegate.EndInvoke(ar);
    UpdateTestResults(portTestResult); // pass the results along to update the UI
}

private void UpdateTestResults(PortTestResult portTestResult)
{
    if (this.ComPortComboBox.InvokeRequired)
    {
        UpdateTestResultsDelegate updateTestResultsDelegate = new UpdateTestResultsDelegate(UpdateTestResults);
        this.Invoke(updateTestResultsDelegate, portTestResult);
    }
    else
    { // set status based on test result
        if (portTestResult.UseThisPort)
        {
            this._autoDetectResults[portTestResult.PortName] = 1;   // 1 for a good response
            this.ComPortComboBox.SelectedItem = portTestResult.PortName;
        }
        else
        {
            this._autoDetectResults[portTestResult.PortName] = -1; // -1 for a bad response
        }
        this.ComPortComboBox.Invalidate();  // force the combobox to redraw with new colors
    }
}


protected override void Dispose(bool disposing)
{
    if (disposing && (components != null))
    {
        components.Dispose();
    }
    base.Dispose(disposing);
}
private void InitializeComponent()
{
    this.components = new System.ComponentModel.Container();
    this.ComPortComboBox = new System.Windows.Forms.ComboBox();
    this.ComPortLabel = new System.Windows.Forms.Label();
    this.MainErrorProvider = new System.Windows.Forms.ErrorProvider(this.components);
    this.autoQueryButton = new System.Windows.Forms.Button();
    ((System.ComponentModel.ISupportInitialize)(this.MainErrorProvider)).BeginInit();
    this.SuspendLayout();
    this.ComPortComboBox.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed;
    this.ComPortComboBox.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList;
    this.ComPortComboBox.FormattingEnabled = true;
    this.ComPortComboBox.Location = new System.Drawing.Point(71, 12);
    this.ComPortComboBox.Name = "ComPortComboBox";
    this.ComPortComboBox.Size = new System.Drawing.Size(136, 21);
    this.ComPortComboBox.DrawItem += new System.Windows.Forms.DrawItemEventHandler(this.ComPortComboBox_DrawItem);
    this.ComPortLabel.Location = new System.Drawing.Point(12, 15);
    this.ComPortLabel.Name = "ComPortLabel";
    this.ComPortLabel.Size = new System.Drawing.Size(53, 13);
    this.ComPortLabel.Text = "&Com Port:";
    this.autoQueryButton.Location = new System.Drawing.Point(213, 11);
    this.autoQueryButton.Name = "autoQueryButton";
    this.autoQueryButton.Size = new System.Drawing.Size(49, 21);
    this.autoQueryButton.Text = "detect";
    this.autoQueryButton.UseVisualStyleBackColor = false;
    this.autoQueryButton.Click += new System.EventHandler(this.autoQueryButton_Click);
    this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.ClientSize = new System.Drawing.Size(282, 47);
    this.Controls.Add(this.autoQueryButton);
    this.Controls.Add(this.ComPortLabel);
    this.Controls.Add(this.ComPortComboBox);
    this.Name = "Demo";
    this.SizeGripStyle = System.Windows.Forms.SizeGripStyle.Hide;
    this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
    this.Load += new System.EventHandler(this.Settings_Load);
    ((System.ComponentModel.ISupportInitialize)(this.MainErrorProvider)).EndInit();
    this.ResumeLayout(false);
    this.PerformLayout();
}
}

public class PortTestResult
{
    public string PortName { get; set; }
    public bool UseThisPort { get; set; }
}
}

Answer 1

这篇 CodeProject 文章提供了有关自定义组合框的大量信息：文章