205 lines
7.3 KiB
C#
205 lines
7.3 KiB
C#
using System;
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using System.Drawing;
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using System.Runtime.InteropServices;
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using System.Windows.Forms;
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namespace AT.STO.UI.Win
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{
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/// <summary>
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/// A class to assist in creating popup windows like Combo Box drop-downs and Menus.
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/// This class includes functionality to keep the title bar of the popup owner form
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/// active whilst the popup is displayed, and to automatically cancel the popup
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/// whenever the user clicks outside the popup window or shifts focus to another
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/// application.
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///
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/// Thousand thanks to Steve McMahon:
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/// http://www.vbaccelerator.com/home/NET/Code/Controls/Popup_Windows/Popup_Windows/Popup_Form_Demonstration.asp
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/// </summary>
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internal class DropDownWindowHelper : NativeWindow
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{
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#region Private Variable Declarations
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private EventHandler DropDownClosedHandler = null;
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private Form _dropDown = null;
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private bool _dropDownShowing = false;
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private DropDownMessageFilter _filter = null;
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private Form _owner = null;
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private bool _skipClose = false;
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#endregion
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#region Event Declarations
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public event DropDownCancelEventHandler DropDownCancel;
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public event DropDownClosedEventHandler DropDownClosed;
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#endregion
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#region Constructor / Destructor
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/// <summary>
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/// Default constructor.
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/// </summary>
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/// <remarks>Use the <see cref="System.Windows.Forms.NativeWindow.AssignHandle"/>
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/// method to attach this class to the form you want to show popups from.</remarks>
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public DropDownWindowHelper()
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{
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_filter = new DropDownMessageFilter(this);
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_filter.DropDownCancel -= new DropDownCancelEventHandler(Popup_Cancel);
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_filter.DropDownCancel += new DropDownCancelEventHandler(Popup_Cancel);
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}
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#endregion
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#region Event Handler
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private void Popup_Cancel(object sender, DropDownCancelEventArgs e)
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{
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OnDropDownCancel(e);
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}
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/// <summary>
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/// Responds to the <see cref="System.Windows.Forms.Form.Closed"/>
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/// event from the popup form.
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/// </summary>
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/// <param name="sender">Popup form that has been closed.</param>
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/// <param name="e">Not used.</param>
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private void Popup_Closed(object sender, EventArgs e)
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{
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CloseDropDown();
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}
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/// <summary>
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/// Subclasses the owning form's existing Window Procedure to enables the
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/// title bar to remain active when a popup is show, and to detect if
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/// the user clicks onto another application whilst the popup is visible.
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/// </summary>
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/// <param name="m">Window Procedure Message</param>
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protected override void WndProc(ref Message m)
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{
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base.WndProc(ref m);
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if (DropDownShowing)
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{
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if (m.Msg == UIApiCalls.WM_NCACTIVATE)
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{
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if (((int)m.WParam) == 0) // Check if the title bar will made inactive:
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{ // Note it's no good to try and consume this message; if you try to do that you'll end up with windows
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UIApiCalls.SendMessage(this.Handle, UIApiCalls.WM_NCACTIVATE, 1, IntPtr.Zero); // If so reactivate it.
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}
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}
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else if (m.Msg == UIApiCalls.WM_ACTIVATEAPP)
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{
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if ((int)m.WParam == 0) // Check if the application is being deactivated.
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{
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CloseDropDown(); // It is so cancel the popup:
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UIApiCalls.PostMessage(this.Handle, UIApiCalls.WM_NCACTIVATE, 0, IntPtr.Zero); // And put the title bar into the inactive state:
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}
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}
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}
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}
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#endregion
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#region Public Methods
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/// <summary>
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/// Shows the specified Form as a popup window, keeping the
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/// Owner's title bar active and preparing to cancel the popup
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/// should the user click anywhere outside the popup window.
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/// <para>Typical code to use this message is as follows:</para>
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/// <code>
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/// frmPopup popup = new frmPopup();
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/// Point location = this.PointToScreen(new Point(button1.Left, button1.Bottom));
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/// popupHelper.ShowPopup(this, popup, location);
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/// </code>
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/// <para>Put as much initialisation code as possible
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/// into the popup form's constructor, rather than the <see cref="System.Windows.Forms.Load"/>
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/// event as this will improve visual appearance.</para>
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/// </summary>
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/// <param name="Owner">Main form which owns the popup</param>
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/// <param name="Popup">Window to show as a popup</param>
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/// <param name="v">Location relative to the screen to show the popup at.</param>
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public void ShowDropDown(Form Owner, Form DropDown, Point Location)
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{
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_owner = Owner;
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_dropDown = DropDown;
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Application.AddMessageFilter(_filter); // Start checking for the popup being cancelled
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DropDown.StartPosition = FormStartPosition.Manual; // Set the location of the popup form:
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DropDown.Location = Location;
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Owner.AddOwnedForm(DropDown); // Make it owned by the window that's displaying it:
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DropDownClosedHandler = new EventHandler(Popup_Closed); // Respond to the Closed event in case the popup is closed by its own internal means
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DropDown.Closed += DropDownClosedHandler;
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_dropDownShowing = true; // Show the popup:
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DropDown.Show();
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DropDown.Activate();
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// A little bit of fun. We've shown the popup, but because we've kept the main window's
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// title bar in focus the tab sequence isn't quite right. This can be fixed by sending a tab,
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// but that on its own would shift focus to the second control in the form. So send a tab,
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// followed by a reverse-tab.
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UIApiCalls.keybd_event((byte) Keys.Tab, 0, 0, 0);
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UIApiCalls.keybd_event((byte) Keys.Tab, 0, UIApiCalls.KEYEVENTF_KEYUP, 0);
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UIApiCalls.keybd_event((byte) Keys.ShiftKey, 0, 0, 0);
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UIApiCalls.keybd_event((byte) Keys.Tab, 0, 0, 0);
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UIApiCalls.keybd_event((byte) Keys.Tab, 0, UIApiCalls.KEYEVENTF_KEYUP, 0);
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UIApiCalls.keybd_event((byte) Keys.ShiftKey, 0, UIApiCalls.KEYEVENTF_KEYUP, 0);
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_filter.DropDown = DropDown; // Start filtering for mouse clicks outside the popup
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}
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/// <summary>
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/// Called when the popup is being hidden.
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/// </summary>
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public void CloseDropDown()
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{
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if (DropDownShowing)
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{
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if (!_skipClose)
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{
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OnPDropDownClosed(new DropDownClosedEventArgs(_dropDown));
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}
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_skipClose = false;
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_owner.RemoveOwnedForm(_dropDown); // Make sure the popup is closed and we've cleaned up:
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_dropDownShowing = false;
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_dropDown.Closed -= DropDownClosedHandler;
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DropDownClosedHandler = null;
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_dropDown.Close();
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Application.RemoveMessageFilter(_filter); // No longer need to filter for clicks outside the popup.
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// If we did something from the popup which shifted focus to a new form, like showing another popup
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// or dialog, then Windows won't know how to bring the original owner back to the foreground, so
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// force it here:
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_owner.Activate();
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_dropDown = null; // Null out references for GC
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_owner = null;
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}
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}
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#endregion
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#region Public Properties
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/// <summary>
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/// Indicator weither the DropDown is showing.
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/// </summary>
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public bool DropDownShowing
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{
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get { return _dropDownShowing; }
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}
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#endregion
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#region Event Implementation
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protected virtual void OnDropDownCancel(DropDownCancelEventArgs e)
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{
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if (this.DropDownCancel != null)
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{
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this.DropDownCancel(this, e);
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if (!e.Cancel)
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{
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_skipClose = true;
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}
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}
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}
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protected virtual void OnPDropDownClosed(DropDownClosedEventArgs e)
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{
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if (this.DropDownClosed != null)
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{
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this.DropDownClosed(this, e);
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}
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}
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#endregion
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}
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}
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