[英]C# WinForms - filtering one combobox based on the value of another combobox in a databound datagridview
[英]C# Winforms: Add an “Select from list…” placeholder to databound combobox
我有一個像這樣數據綁定的組合框:
comboBox.InvokeIfRequired(delegate
{
var data = db.GetData();
comboBox.DisplayMember = "Value";
comboBox.ValueMember = "ID";
comboBox.DataSource = data;
});
它工作正常,但它預先選擇了第一個數據綁定值。 我希望使用像“從列表中選擇項目......”這樣的占位符來預先選擇組合框。
這樣做的最佳方式/方法是什么?
a)添加數據變量空項
b)通過combobox
變量屬性設置它? 如果是這樣,哪些?
c)其他
我在這里找到了解決方案
這個代碼是:
private const int EM_SETCUEBANNER = 0x1501;
[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern Int32 SendMessage(IntPtr hWnd, int msg, int wParam, [MarshalAs(UnmanagedType.LPWStr)] string lParam);
[DllImport("user32.dll")]
private static extern bool GetComboBoxInfo(IntPtr hwnd, ref COMBOBOXINFO pcbi);
[StructLayout(LayoutKind.Sequential)]
private struct COMBOBOXINFO
{
public int cbSize;
public RECT rcItem;
public RECT rcButton;
public UInt32 stateButton;
public IntPtr hwndCombo;
public IntPtr hwndItem;
public IntPtr hwndList;
}
[StructLayout(LayoutKind.Sequential)]
private struct RECT
{
public int left;
public int top;
public int right;
public int bottom;
}
public static void SetCueText(Control control, string text)
{
if (control is ComboBox)
{
COMBOBOXINFO info = GetComboBoxInfo(control);
SendMessage(info.hwndItem, EM_SETCUEBANNER, 0, text);
}
else
{
SendMessage(control.Handle, EM_SETCUEBANNER, 0, text);
}
}
private static COMBOBOXINFO GetComboBoxInfo(Control control)
{
COMBOBOXINFO info = new COMBOBOXINFO();
//a combobox is made up of three controls, a button, a list and textbox;
//we want the textbox
info.cbSize = Marshal.SizeOf(info);
GetComboBoxInfo(control.Handle, ref info);
return info;
}
然后你可以像這樣簡單地使用它:
SetCueText(comboBox, "text");
這也適用於文本框。
只需使用Text Property並在那里寫“從列表中選擇項目......”
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