C# 为什么设置 DroppedDown 时 ComboBox 隐藏光标？
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Why ComboBox hides cursor when DroppedDown is set?
提问by Ivan Danilov
Let's create WinForms Application (I have Visual Studio 2008 running on Windows Vista, but it seems that described situation takes place almost everywhere from Win98 to Vista, on native or managed code).
让我们创建 WinForms 应用程序（我在 Windows Vista 上运行 Visual Studio 2008，但似乎描述的情况几乎发生在从 Win98 到 Vista 的任何地方，在本机或托管代码上）。
Write such code:
写这样的代码：
using System;
using System.Drawing;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public class Form1 : Form
{
private readonly Button button1 = new Button();
private readonly ComboBox comboBox1 = new ComboBox();
private readonly TextBox textBox1 = new TextBox();
public Form1() {
SuspendLayout();
textBox1.Location = new Point(21, 51);
button1.Location = new Point(146, 49);
button1.Text = "button1";
button1.Click += button1_Click;
comboBox1.Items.AddRange(new[] {"1", "2", "3", "4", "5", "6"});
comboBox1.Location = new Point(21, 93);
AcceptButton = button1;
Controls.AddRange(new Control[] {textBox1, comboBox1, button1});
Text = "Form1";
ResumeLayout(false);
PerformLayout();
}
private void button1_Click(object sender, EventArgs e) {
comboBox1.DroppedDown = true;
}
}
}
Then, run app. Place mouse cursor on the form and don't touch mouse anymore. Start to type something in TextBox - cursor will hide because of it. When you press Enter key - event throws and ComboBox will be dropped down. But now cursor won't appear even if you move it! And appears only when you click somewhere.
然后，运行应用程序。将鼠标光标放在表单上，不要再触摸鼠标了。开始在 TextBox 中输入内容 - 光标将因此隐藏。当您按 Enter 键时 - 事件会引发并且 ComboBox 将被下拉。但是现在即使移动光标也不会出现！并且仅在您单击某处时出现。
ThereI've found discussion of this problem. But there's no good solution...
在那里我找到了关于这个问题的讨论。但是没有什么好的解决办法...
Any thoughts? :)
有什么想法吗？:)
采纳答案by Daniel Stutzbach
I was able to work around the problem like this:
我能够解决这样的问题：
comboBox1.DroppedDown = true;
Cursor.Current = Cursors.Default;
回答by Lazarus
For a start, it's a very obscure set of circumstances that I can't imagine being a useful interface action.
首先，这是一组非常模糊的情况，我无法想象这是一个有用的界面操作。
It would seem to be a bug that causes the programmatic dropdown to start editing in the text box that forms part of the dropdown control so effectively double hiding the cursor. To break it down...
这似乎是一个错误，导致编程下拉列表在构成下拉控件一部分的文本框中开始编辑，因此有效地双重隐藏了光标。为了打破它...
I'd suspect that each hide stores the state of the cursor and restores it on exit.
我怀疑每个隐藏都存储光标的状态并在退出时恢复它。
The text box has stored the actual cursor state and hidden it.
文本框存储了实际的光标状态并将其隐藏。
The dropdown causes the hidden state to be stored and the cursor set to hidden. When you move the cursor it probably does restore it but to the hidden state it saved so the cursor remains hidden.
下拉列表会导致隐藏状态被存储并且光标设置为隐藏。当您移动光标时，它可能会恢复它，但会恢复到它保存的隐藏状态，因此光标保持隐藏状态。
A click on the form seems to force a reset of that situation, not sure why on that but that's my 2 penneth worth.
单击表单似乎会强制重置这种情况，不知道为什么会这样，但那是我的 2 Penneth 值。
回答by Ivan Danilov
In fact I was able to resolve this issue in this way:
事实上，我能够通过这种方式解决这个问题：
#region Dirty methods :)
#pragma warning disable 169
[DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
public static extern void mouse_event(long dwFlags, long dx, long dy, long cButtons, long dwExtraInfo);
private const int MOUSEEVENTF_ABSOLUTE = 0x8000;
private const int MOUSEEVENTF_MOVE = 0x1;
private const int MOUSEEVENTF_LEFTDOWN = 0x02;
private const int MOUSEEVENTF_LEFTUP = 0x04;
private const int MOUSEEVENTF_RIGHTDOWN = 0x08;
private const int MOUSEEVENTF_RIGHTUP = 0x10;
#pragma warning restore 169
#endregion
private void button1_Click(object sender, EventArgs e) {
Point oldCursorPos = Cursor.Position; // save pos
Point a = comboBox1.Parent.PointToScreen(comboBox1.Location);
a.X += comboBox1.Width - 3;
a.Y += comboBox1.Height - 3;
Cursor.Position = a;
// simuate click on drop down button
mouse_event(MOUSEEVENTF_LEFTDOWN | MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
Cursor.Position = oldCursorPos; // restore pos
}
But it is not the solution I want :( It is rather a crutch but not a solution.
但这不是我想要的解决方案:(它是一个拐杖，但不是一个解决方案。
回答by Kev
It's a strange set of circumstances where the combo box is a DropDownListtype and you call the DroppedDownmethod on the combo box from within the code either while it has the focus or not.
这是一组奇怪的情况，其中组合框是一种DropDownList类型，您DroppedDown在代码中调用组合框上的方法，无论它是否具有焦点。
The cursor will disappear as though behind the form. If you click the form the cursor comes back but the combo box closes so not a good result.
光标将消失，就像在表单后面一样。如果您单击表单，光标会返回，但组合框会关闭，因此效果不佳。
I can confirm that this code fixes the issue without closing the combo box list.
我可以确认此代码无需关闭组合框列表即可解决问题。
cbo_VisitorTypes.DroppedDown = true;
Cursor.Current = Cursors.Default;
