Develop Reference

Assign a Keyboard key to a button click WINFORM

I am developing a small application with some buttons and textbox. What I am having problem is assigning a keyboard key (e.g. F3) to a button click.
For example if the user click the button Cash the code I wanted it's executed fine, but I want to make more easier instead clicking the button with mouse, I want the user be able to press the key on keyboard. I used the keydown event, also keypress event of that button, but still nothing.
I tried this keydown event
if (e.KeyCode == Keys.Enter)
{
btncash.PerformClick()
}
But still nothing

Do not use F3 function button it's used by OS for activating search. Enter key is fairs click event on focused control so do not use this also. Implement as suggested below.
In your Main form
Set KeyPreview to True in form load event.
Add KeyDown event handler with the following code
private void Form1_KeyDown(object sender,
KeyEventArgs e)
{
if (e.Control && e.KeyCode == Keys.H)
{
btncash.PerformClick();
//btncash_Click(null, null);
}
}

Focus in parent even if click on child element

I have a UserControl (let's call it "PresentationCell") which contains a label, and an PictureBox.
In another control, which is using this PresentationCell, I have added an event
presentationCell.GotFocus += OnFocus;
private void OnFocus(object sender, EventArgs e)
{
if (sender is PresentationCell current)
current.BackColor = Color.Azure;
}
This will not be fired, if I click / focus on the Label or PictureBox that is within the PresentationCell.
How can I make it fire, when just something within the PresentationCell is in focus?

The problem here is, that the Label and PictureBox controls aren't selectable controls, so they aren't able to receive focus from mouse clicks.
What you could to instead, is to handle the mouse click event and check if you have hit the PresentationCell. If the PresentationCell is hit you can programatically set the focus like so:
hitPresentationCell.Focus();
This will then fire the GotFocus event.
In your OnFocus method you will have to switch the focus to another control or the event will fire endlessly.

Winform Checkbox MouseDown event handler not allowing CheckedChanged event to fire

I have a WinForm which contains a multitude of controls interdependent on each other for their visibility and content.
I have a pair of radio buttons, controlling a combobox's (ComboBoxA) enable/disable flag and content. The selection on this combobox controls the visibility of a checkbox. The checking of this checkbox controls another combobox's (ComboBoxB) visibility and content. Business requirements are quite complicated around these controls. As a result, I require the ability to fire of the events programmatically and through user action, doing different things in each case.
In the checkbox's case, I check it programmatically while loading data (if needed), which fires the CheckedChanged event which in turn does additional action controlling ComboBoxB. The code for this is pretty vanilla, nothing special, but my question is more theoretical than practical. Please keep reading.
Due to this requirement, I need a way to distinguish between programmatic checking and user action. I tried using the Click event and CheckedChanged event, setting a flag in the click event, signifying user action. Unfortunately, the CheckedChanged event fires before the Click event, dead-ending this trick.
Now, I tried using the MouseDown event to capture user action. But funnily enough, once the event fires, checkbox remains unchecked and the CheckedChanged event doesnt fire.
Now, I have managed to use a flag in the code to determine programmatic checking and use that to distinguish between the two, but I was curious as to why the MouseDown event didnt allow the checkbox to be checked. Any ideas? I searched online but either I didnt do a thorough job of it, or google is not returning the right results for me. I apologize if anybody is actually able to find a google result for this problem.

It's something else in your code, not the MouseDown event that's preventing the CheckChanged to be fired.
Here is how I know this:
I've added a checkbox and a button to an empty form, and added event handlers to Click on the button, and on the checkbox CheckedChanged, KeyDown and MouseDown events. I've also added to the form a string variable called LastEventRaised, and in the CheckedChanged I've simply shown a MessageBox:
string LastEventRaised = string.Empty;
private void checkBox1_CheckedChanged(object sender, EventArgs e)
{
MessageBox.Show("Checked changed " + LastEventRaised);
LastEventRaised = string.Empty;
}
private void checkBox1_KeyDown(object sender, KeyEventArgs e)
{
LastEventRaised = "KeyDown";
}
private void checkBox1_MouseDown(object sender, MouseEventArgs e)
{
LastEventRaised = "MouseDown";
}
private void button1_Click(object sender, EventArgs e)
{
LastEventRaised = "programmatically";
checkBox1.Checked = !checkBox1.Checked;
}
Each time the message box popped up I've got the correct message.

How to prevent clicks from passing through a control to the one below it

I have a textbox in a groupbox, both with double click events. When I double click in the textbox both events are triggered.
How do I stop clicks in the textbox from passing through to the groupbox? I've tried putting "e.Handled = true;" at the end of the textbox_DoubleClick event but this makes no difference.

Because WPF uses a "tunneling / bubbling" model of event propagation, most events begin bubbling UP from the bottom of the visual tree. If you want to catch an event on the way down, there are Preview versions of the events that tunnel downwards. For example:
PreviewMouseDoubleClick
Set e.Handled = true in there.

In your GroupBox's DoubleClick event you could check the value of e.OriginalSource and if that value is not the GroupBox, ignore the event
private void TabItem_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
if (e.OriginalSource is GroupBox)
{
// Your code here
}
}
I believe ClickEvents are actually Direct Events, and not Tunneled/Bubbled events, so setting e.Handled in one won't cancel the other.
Per MSDN Site for MouseDoubleClick
Although this routed event seems to follow a bubbling route through an
element tree, it actually is a direct routed event that is raised
along the element tree by each UIElement.

you should handle e.Handled in the PreviewDoubleClick because tunneled events happens before bubbled up ones.
also why would you need to handle that event in both textbox and groupbox ? as it is getting fired in both because 2 separate events are getting fired.

Equivalent of WinForms TextBox.Validating event in WPF

In WinForms I could handle the Validated event to do something after the user changed text in a TextBox. Unlike TextChanged, Validated didn't fire for every character change; it only fired when the user was done.
Is there anything in WPF I can use to get the same result, an event raised only after the user is done changing the text?

LostFocus will fire when the user moves from your textbox onto any other control.

It seems that there is no native solution.
The LostFocus event is a good idea. But when the user click on Enter, he wants the TextBox to validate the change.
So here is my suggestion : use the LostFocus event and the KeyDown event when the key is Enter.
private void TextBox_LostFocus(object sender, RoutedEventArgs e)
{
// code to lauch after validation
}
private void TextBox_KeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Enter)
{
// call the LostFocus event to validate the TextBox
((TextBox)sender).RaiseEvent(new RoutedEventArgs(TextBox.LostFocusEvent));
}
}

LostFocus is not equivalent to Validate. It creates lots of problem when you have multiple text boxes on one screen and every text box has some logic written in Validate. In validate event you can control focus easily but not in LostFocus so easily.

You can also try Binding.ValidationRules
Documented at : http://msdn.microsoft.com/en-us/library/system.windows.data.binding.validationrules.aspx
Here is the article to get started:
How to implement binding validations :
http://msdn.microsoft.com/en-us/library/ms753962.aspx