I have a WPF Window loaded. But on event of sizeChanged, it fires twice. May I know why?
Also, I have tried adding 'e.handled = true'
Yeah, I've noticed the same thing. If you look at the value for e.NewSize you'll see they are different values, with the final time being the correct size. It must be something in the way it gets laid out.
Related
A custom WPF Control overrides OnRender. The method generates and displays a Path from custom data. The data provider is bound using a Dependency Property. The Dependency Property registers for an event when data changed. This event in turn calls InvalidateVisual().
However, after the InvalidateVisual() the OnRender is not always called.
We use the Prism Framework and the Region functionallity. The Control in question is embedded in such a Region, which is activated and deactivated. However, the Control's property "IsVisible" is true whenever the region is active. But still, when calling InvalidateVisual() the OnRender method is not called...
What could prevent the OnRender method from being called?
I just had this problem, too.
Context
I've got a load of controls based on the DynamicDataDisplay graph components inside a VirtualizingStackPanel (inside a ListBox).
When there are more controls that are visible at once, but not enough for the VirtualizingStackPanel to start re-using them when you scroll then I see this issue with the D3 AxisControl class. For some reason it does a lot of work in it's OnRender method, which it tries to trigger by calling InvalidateVisual when something changes.
In the problem case the problem controls call InvalidateVisual but they never get a call to MeasureOverride, ArrangeOverride or OnRender. Interestingly, most of the controls still work, in one particular problem case I get the last 3 out of a set of 11 failing to work properly. Notably those 3 (and only those 3) receive a call to MeasureOverride immediately before the data binding update that triggers the call to InvalidateVisual.
My Fix
In the end I managed to fix it by adding a call to InvalidateMeasure alongside the call to InvalidateVisual.
It's a horrible solution, but it's not a performance critical part of our application, so I seem to be getting away with it.
If the size of your control is staying the same, you should not be using InvalidateMeasure() or InvalidateVisual() because they trigger an expensive re-layout.
WPF is a retained drawing system. OnRender() might be better called AccumulateDrawingObjects(), because it doesn't actually draw. It accumulates a set of drawing objects which WPF uses to draw your UI whenever it wants. The magic thing is, if you put a DrawingGroup into the DrawingContext during OnRender(), you can actually efficiently update it after OnRender, anytime you like.
See my answer here for more details..
https://stackoverflow.com/a/44426783/519568
I just had this problem, too.
I had a scrollbar for a control which only figured out during OnRender() how much space is really needed to display all content, which could be bigger than the available display space and therefor needed a scrollbar. It could happen that OnRender() called some methods which ultimately changed the value of the scrollbar which was supposed to start OnRender() with InvalidateVisual().
However, OnRender() did not get called again after InvalidateVisual(). I guess the reason is that InvalidateVisual() sets some flags which tells WPF that the control needs to get drawn again, but once OnRender() finishes, that flag gets reset. Here some pseudo code how I expect it to happen:
//someCode:
control.InvalidateVisual()
//code of InvalidateVisual()
control.RedrawFlag = true;
//WPF some time later:
if (control.RedrawFlag){
control.OnRender()
//OnRender code
//do some stuff
//decide control needs to be redrawn
//however, RedrawFlag is alreday true!
//next line is not changing anything
control.RedrawFlag = true;
//WPF finished executing control.OnRender
control.RedrawFlag = false;
}
I didn't further investigate if WPF really works this way, but it would explain why OnRender() does not get called a second time.
Instead of wasting even more time, I changed how to calculate the total width of the control content can be and put this code outside of OnRender().
I am using a standard TreeView in a WinForms application and everything works fine except for one issue:
Parts of the system need to change depending on the selected TreeNode, which works fine using the AfterSelect event.
However, sometimes the TreeView will get cleared completely resulting in an empty selection which does not trigger this event.
At the momemnt I am calling the event callback manually to fix this issue.
This is obviously dangerous, since I will forget to call this function somewhere. Is there a "correct" way to do this?
Thank You!
This is by design. The underlying native Windows controls only generate notifications for things you cannot figure out yourself. The ListBox control for example doesn't have any event that tells you an item got added or removed. Which is because there is no way for the user to add or remove items. Similarly, there's no way for the user to remove the nodes from a tree view.
These kinds of changes requires code that you write. Since it is your code, you cannot not know that these changes happened. If you want an event then you'll have to raise it yourself. Beware that this is harder than it looks, the TreeNodeCollection class doesn't reliably let you generate an event for programmatic changes to the node collection. It doesn't behave like an ObservableCollection. You are definitely better off by not needing this event.
I have a FlowDocumentPageViewer control that I am populating from the code behind. I am adding text from 3-4 items. I need to know on what page item 1,2,3... ends.
These items get added to a FlowDocument in a loop and then at the end I have
flowDocumentPageViewer.Document = resultsDocument;
However, even then if I call
flowDocumentPageViewer.PageCount
I still get 0. If I do some event like a click and print the above PageCount after the window renders, it does print the correct value. However, I need a running total of this value as I populate the FlowDocument. I am hoping someone knows some kind of trick with text metrics or any other way that this could be solved.
You have no choice but to trigger a (virtual) render of your control to get this kind of info.
the easiest way is to force a updateLayout() on the FlowDocumentPageViewer, but this means it'll show the result before you get the info which is probably not what you want.
you can also use the Arrange() method if you don't want the content to be shown:
http://msdn.microsoft.com/en-us/library/system.windows.uielement.arrange.aspx
after using this on your control you should get the updated info.
I had the same problem and to be honest I still do. Any updateLayout() did not help. Now I use a timer to get the pagecount a second later after I assigend to document to the viewer. Works fine.
have a TextBox item (MyTextBox) on a TabItem control. I have code that looks as follows:
MyTextBox.Focus();
Keyboard.Focus(MyTextBox);
When I run this code through the debugger I see the following after the lines are executed:
MyTextBox.IsFocused = true
MyTextBox.IsKeyboardFocused = false
Can anyone tell me why the textbox isn't receiving keyboard focus? It's just a standard TextBox control that is enabled.
When you try to set Focus to an element besides the things enumerated above by our coleague, you must also know that WPF does not allow cross threaded operations.
In some cases this exception is not raised like in the Focus method call case. What I've done to fix this issue is to call all the code that involves Keyboards focus in an action.
This action is ran inside the control dispatcher to make sure that my code is not being executed from another thread than the UI thread (e.g. timer event or an event raised from another thread):
[UIElement].Dispatcher.BeginInvoke(
new Action(
delegate{
/// put your Focus code here
}
)
);
MyTextBox.IsKeyboardFocused is false because you are looking at it under debugger and the keyboard focus is probably in your Visual Studio... Try debugging focus without breakpoints (e.g. Debug.Write or trace brakepoints) to see actual values of MyTextBox.IsKeyboardFocused in runtime.
Also notice that Focus() method returns boolean value that indicates whether focus was successfully set. Does it return False in your case? If yes, I would suggest stepping into Focus() method in order to find out what is wrong.
3 important properties must be true: IsVisible="True", Focusable="True". IsEnabled="True".
To be focusable, Focusable and IsEnabled must both be true.
http://msdn.microsoft.com/en-us/library/system.windows.uielement.focus.aspx
The accepted answer here does not solve the problem of textboxes who dont gain focus, no matter what the debugger tells you. If you have and can write to your textbox, then you have it keyboard-focused.
I found this here solving the problem (and actually gaining focus, not just settings the values so it looks like focus in the debugger), it comes very close to Pavlov's answer but with the "Focus code" : Keyboard.Focus does not work on text box in WPF
This worked for me (had to do UpdateLayout, otherwise Focus() didn't work immediately after changing tab from script)
tabControl.SelectedIndex = 2;
this.UpdateLayout();
txtMyTextBox.Focus();
It's important where your first two lines of code are executed.
If they are in an event handler that relates to the user pressing a key, using the mouse, altering the visibility of a control, or otherwise taking an action that might have an impact on focus, I find manually calling Focus() often doesn't work.
My theory is that internally, WPF operates as follows:
User or code takes action which could have an impact on focus, e.g. a TextBox control becomes enabled inside a focus scope which previously had no focusable control.
WPF notifies various event handlers, including yours which calls Focus().
WPF updates focus based on the state changes in step 1. This overrides whatever you did in step 2.
That is why this answer suggests to call your Focus() in a queued callback which will be executed after step 3.
Side note: you don't need to call both UIElement.Focus and Keyboard.Focus since the first includes the second (at least if you trust the Microsoft docs).
In conclusion, replace your first two lines of code with this:
// using System.Windows.Threading;
Dispatcher.BeginInvoke(DispatcherPriority.Input, MyTextBox.Focus);
I'm using DatePicker and TimePicker from the toolkit. I've got to hook up on the SelectedDateChanged event and I'm also setting the values in code.
My issue is that when I initialise both controls the SelectedDateChanged event doesn't get fired synchronously. That's quite a big issue for me because it means I initialise the control and some time later the event gets fired and changes the current value (because that's what I do in the event handler).
Is there any work around? I tried to listen to some event that get fired once everything is initialized but there's nothing apart from the Loaded event of each control (which is really ugly and gets fired each time the tab on which the controls are gets activated).
EDIT: my problem seemed to go away for a while so I didn't bother looking into it in case it came back. Now it did :(
I use MVVM and initialize the controls within the view in the constructor. Then, when the VM gets the view, it sets the default value as well.
Unfortunately, by the time the VM sets the value the controls haven't got initialized and happen to get themselves intialized some time later (even though I set them in the constructor). They then override the default values.
There's definitely an issue. However I found a very easy workaround: if I bind the control and don't listen to the SelectedDate event I get the change synchronously and everything works fine.
Took me ages to figure that out but now it's working.