When the user clicks on certain part of a window, I add a UserControl to the window's controls. The UserControl has a close button. What can I do in the UserControl's button handler to destroy the UserControl? There seems to be no .net analog to the Win32 DestroyWindow call, and there is no Close() method for a control. So far I have this:
private void sbClose_Click(object sender, EventArgs e)
{
Parent.Controls.Remove(this);
this.Dispose();
}
And, in case the parent needs to destroy the control, what are the steps? This is what I have so far:
Controls.Remove(control);
control.Dispose();
You're working in a managed code environment with garbage collection - there's nothing you can do to force the user control to be destroyed.
All you need to do, all you can do is to remove it from the parent and make sure there are no remaining references.
This will generally be sufficient:
private void sbClose_Click(object sender, EventArgs e)
{
Parent.Controls.Remove(this);
}
The only time you'll need more is if you tie things together with events, as you'll need to deregister those as well.
A control can't destroy itself. In terms of having a parent do it, you are on the right track. You can have the parent or another control call Dispose on it and remove all references to this control. Dereferencing the control this way will allow the GC to clean things up.
Related
I've written a Windows Forms app where I do custom drawing on a Panel using Control.CreateGraphics(). Here's what my Form looks like at startup:
The custom drawing is performed on the top panel in the Click event handler of the "Draw!" button. Here's my button click handler:
private void drawButton_Click(object sender, EventArgs e)
{
using (Graphics g = drawPanel.CreateGraphics())
{
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
g.Clear(Color.White);
Size size = drawPanel.ClientSize;
Rectangle bounds = drawPanel.ClientRectangle;
bounds.Inflate(-10, -10);
g.FillEllipse(Brushes.LightGreen, bounds);
g.DrawEllipse(Pens.Black, bounds);
}
}
After a click on drawButton, the form looks like this:
Success!
But when I shrink the form by dragging a corner...
...and expand it back to its original size,
part of what I drew is gone!
This also happens when I drag part of the window offscreen...
...and drag it back onscreen:
If I minimize the window and restore it, the whole image is erased:
What is causing this? How can I make it so the graphics I draw are persistent?
Note: I've created this self-answered question so I have a canonical Q/A to direct users to, as this is a common scenario that's hard to search for if you don't already know the cause of the problem.
TL;DR:
Don't do your drawing in response to a one-time UI event with Control.CreateGraphics. Instead, register a Paint event handler for the control on which you want to paint, and do your drawing with the Graphics object passed via the PaintEventArgs.
If you want to paint only after a button click (for example), in your Click handler, set a boolean flag indicating that the button has been clicked and then call Control.Invalidate(). Then do your rendering conditionally in the Paint handler.
Finally, if your control's contents should change with the size of the control, register a Resize event handler and call Invalidate() there too.
Example code:
private bool _doCustomDrawing = false;
private void drawPanel_Paint(object sender, PaintEventArgs e)
{
if (_doCustomDrawing)
{
Graphics g = e.Graphics;
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
g.Clear(Color.White);
Size size = drawPanel.ClientSize;
Rectangle bounds = drawPanel.ClientRectangle;
bounds.Inflate(-10, -10);
g.FillEllipse(Brushes.LightGreen, bounds);
g.DrawEllipse(Pens.Black, bounds);
}
}
private void drawButton_Click(object sender, EventArgs e)
{
_doCustomDrawing = true;
drawPanel.Invalidate();
}
private void drawPanel_Resize(object sender, EventArgs e)
{
drawPanel.Invalidate();
}
But why? What was I doing wrong, and how does this fix it?
Take a look at the documentation for Control.CreateGraphics:
The Graphics object that you retrieve through the CreateGraphics method should not normally be retained after the current Windows message has been processed, because anything painted with that object will be erased with the next WM_PAINT message.
Windows doesn't take responsibility for retaining the graphics you draw to your Control. Rather, it identifies situations in which your control will require a repaint and informs it with a WM_PAINT message. Then it's up to your control to repaint itself. This happens in the OnPaint method, which you can override if you subclass Control or one of its subclasses. If you're not subclassing, you can still do custom drawing by handling the public Paint event, which a control will fire near the end of its OnPaint method. This is where you want to hook in, to make sure your graphics get redrawn every time the Control is told to repaint. Otherwise, part or all of your control will be painted over to the control's default appearance.
Repainting happens when all or part of a control is invalidated. You can invalidate the entire control, requesting a full repaint, by calling Control.Invalidate(). Other situations may require only a partial repaint. If Windows determines that only part of a Control needs to be repainted, the PaintEventArgs you receive will have a non-empty ClipRegion. In this situation, your drawing will only affect the area in the ClipRegion, even if you try to draw to areas outside that region. This is why the call to drawPanel.Invalidate() was required in the above example. Because the appearance of drawPanel needs to change with the size of the control and only the new parts of the control are invalidated when the window is expanded, it's necessary to request a full repaint with each resize.
I have a user control which is having a listview inside it. The SelectionChanged event of this list view is handled inside the user control. The code for the same is as follows:
private void lstvMyView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{...}
I want to call this handler again from some other place inside the user control. So to call this handler i need the "SelectionChangedEventArgs" there. When I am trying to create the instance of "SelectionChangedEventArgs", i am unable to understand what should I pass as parameters to the constructor of "SelectionChangedEventArgs".
The place from where I am suppose to call this handler does not add or remove any items in the listview. It just navigates in the items in the listview thereby changing the selectedindex of the listview.
I am trying to do something like this. The below code is obviously incorrect.
lstvMyView_SelectionChanged(_lstvMyView, new SelectionChangedEventArgs());
I want to call this handler again from some other place inside the user control
Don't. An event handler is not supposed to be called explicitly from your code. Whatever you're doing in this handler, you can put it in another method that only takes the parameters it needs, and call that method from your code.
The SelectionChangedEventArgs can be instantiated for unit testing as follows:
new SelectionChangedEventArgs(
System.Windows.Controls.Primitives.Selector.SelectionChangedEvent,
new List<CustomViewModel> { },
new List<CustomViewModel> { customViewModel }
)
Beware that both the removedItems and addedItems cannot be null so an empty collection should be passed.
I'm creating a simple editor within our application using the WPF RichTextBox. Above it I've added the reguslar buttons like Bold, Italic, etc. These buttons use the RichTextBox's commands to set these properties, but next to these buttons, the commands also get send with CTRL+B, CTRL+I, etc. I want these buttons to represent the current state of the RichTextBox at the cursor. I already found out how to get this state and it works when I update this state on the SelectionChanged event. This event ofcourse isn't fired when Bold is toggled so there is no direct feedback.
I would like to know if there is a way to listen to the commands being called, without affecting its original behaviour or some other ideas to solve my problems.
I tried listening to the command the following way:
CommandBinding boldBinding = new CommandBinding(EditingCommands.ToggleBold, CommandExecuted);
_richTextBox.CommandBindings.Add(boldBinding);
and
private void CommandExecuted(object sender, ExecutedRoutedEventArgs e) {
UpdateProperties();
e.Handled = false;
}
This did update the properties, but the RichTextBox didn't seem to receive the command anymore.
I also tried to make my own commands on the control containing the RichTextBox, but when CTRL+B is pressed when the RichTextBox has focus, the original RichTextBox commands are called instead of the new one.
Many thanks in advance!
Liewe
In order to listen to the commands being called, you can use the events raised by CommandManager: Executed or PreviewExecuted.
If you change your XAML to:
<RichTextBox x:Name="_richTextBox" ...
CommandManager:PreviewExecuted="OnRichTextBoxCommand" ... />
you get the OnRichTextBoxCommand method called right before the command is executed. Unfortunately, using the Executed attached event does not work.
This method is called for each event, so you have to filter them:
private void OnRichTextBoxCommand(object sender, ExecutedRoutedEventArgs e) {
if (e.Command == EditingCommands.ToggleBold) {
UpdateProperties();
}
}
It may be even a bit more complex, as the current selection may not have changed when this method is called, so you have to post yourself a message, e.g. like this:
Dispatcher.BeginInvoke(new Action(UpdateProperties));
(if you reference already System.Core, you have the Action type, otherwise define a delegate taking no parameter and returning void, and use in instead.)
is there a way I can get a Load event for System.Windows.Forms.Control just like System.Windows.Forms.Form.Load?
I want to run some initialize code before the control first shown.
Also, it would be nice to be able to do the same for System.Windows.Forms.ToolStripStatusLabel which is not actually a Control, but works like one.
Ideally, I can do this:
control.OnLoad(() => { dosomething here; });
in which OnLoad is a extension method that would run the argument Action when the "control" "Loads".
Thanks!
Form.Load event is called by the OnLoad method which is called from the OnCreateControl method which belongs to the Control class. So for the form the calling sequence would be following:
OnCreateControl start
OnLoad start
Form Load event call
OnLoad finish
OnCreateControl finish
I guess you can override OnCreateControl for your component and add your optimization code there.
Hope this helps, Regards.
For a control you can override either OnControlCreated or OnHandleCreated. The latter one can fire multiple times if it is necessary to recreate the control window. Be sure to use it if your code affects the window itself. In other words, if you do anything that requires the Handle property.
Few suitable choices for a ToolStripItem derived control. I'd recommend overriding SetVisibleCore() or OnAvailableChanged() or the AvailableChanged event. They run when the Visible property of the ToolStripItem changes. Beware that it may fire multiple times, keep a bool field that tracks that your initialization code has already run.
Last but not least, be sure to only do any of this if your code actually requires the control to be created. The vast majority of init code can go in the constructor. You only need a Load event if your code depends on the actual Location and Size of the control. Which might be different from the designer value if the form rescales itself due to a different system font or video DPI setting on the target machine.
I needed a solution like this for a TabPage within a TabControl.The only thing I came up with was using the paint event handler. I added the event handler for Paint and in the very first line I remove the event handler and then do more initialization code. This only works if you do nothave any custom painting. Alternatively, if you do need to do custom painting you could add a flag to check for each time Paint Executes.
//Paint only runs once
private void tabPage1_Paint(object sender, PaintEventArgs e)
{
tabPage1.Paint -= tabPage1_Paint;
//Do initialization here
}
/////////////////////////////////////////////////////////////////////////////////
//Paint always runs
private bool IsFirstPaint = true;
private void tabPage1_Paint(object sender, PaintEventArgs e)
{
if(IsFirstPaint)
{
IsFirstPaint = false;
//Do initialization here
}
//Do custom painting here
}
I have a Window that contains a custom UserControl. The UserControl needs to know when the Window containing it has been closed so that it can terminate a thread.
My best guess as to how to accomplish this is to handle the UserControl's Unloaded event. However, the Unloaded event only seems to be firing when the user actually clicks to close the window, but not when I programmatically call the Close() method on the window.
For reference sake, here are some of the relevant parts of my code.
MyWindow.xaml:
<Window x:Class="Namespace.MyWindow"
xmlns:controls="clr-namespace:Namespace.Controls">
<controls:MyControl/>
</Window>
MyControl.xaml:
<UserControl x:Class="Namespace.Controls.MyControl"
Unloaded="UserControl_Unloaded"/>
<!-- Stuff -->
</UserControl>
MyControl.xaml.cs:
void UserControl_Unloaded(object sender, RoutedEventArgs e)
{
// Stop the thread.
}
So just to recap, the UserControl_Unloaded() method above is getting called when I close the window "manually" (alt-F4, click the red "X", etc.), but not when from elsewhere in the code I call myWindow.Close(). Any ideas?
Turns out the answer in this question solves the problem for me, too. It still seems strange, though, that the Unloaded event isn't getting fired. Go figure.
In MyWindow class
this.Closing += new System.ComponentModel.CancelEventHandler(Window1_Closing);
void Window1_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
call User Control Method()
}
Why just not connect handler to the window.Closed event? Your UserControl can walk through ui tree to find the window.