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Clicking of a button with the help of 'A' key from keyboard in c#

Assume that i am creating a button for counter application, here i need to click the button with the help of a keyboard key instead of mouse click. Anyone can help with that function.

If you want to use Alt + A instead of button , which is access key for your button you can refer to the https://msdn.microsoft.com/en-in/library/ms178233.aspx

As said in another answer Alt + the key is a button shortcut. One way in WinForms is to stick & in front of the character in the button text that you want to use to activate the button. E.g. if the button text is "ABC", change it to "&ABC". Then Alt-A can be used to activate the button. & is how button shortcuts are defined.
For WPF use AccessText or, without using Alt, key bindings: Assign Short Cut Key to a button in WPF

If you are working on windows app
You should add an event to the form, where the user is expected to press the key
Right click on the object that should receive the key press (the body of the form)
Go to properties page
Click on the thunder icon (Events)
Go to the KEY section
Double click on Key Down
Write the following:
if (e.KeyValue == 65) MessageBox.Show("You clicked the letter A. Code of B is 66, and so on");
To discover the KeyValue of the key pressed by the user:
MessageBox.Show(e.KeyValue.ToString());

Handle button which has drill-down menu

So i have a UI that when you right click on a button, it opens a screen with 3 other buttons on it. How do i get the event system to not override the last button clicked (being what i right clicked to open the screen) when i click down on the button that is opened. The only way i can think to do it is to store the button that was right clicked in another variable. I was wondering if there was a way to prevent the event system from overriding the last button pressed. So that my code will run off what was right clicked and not the button that was clicked.

C# WIndows phone disable button after one press

I'm making a Windows Phone 8.1 app in Visual Studio 2013.
I have a page where a user sees an image and button labelled "Complete". The user has to do (in real life) what is in the image, and then press the button. After the button is pressed he is awarded 3 points.
Once the user presses the button, the first time, I would like to disable it. Right now, there is a bug where the user can press it many times and gain more points from one task.

Try doing this:
Button myButton = FindName("ButtonName") as Button;
myButton.IsEnabled = false;
For more information check this: Disable button in WPF?

when I pressed enter it goes direct to the button

I am developing web form in asp.net inside it there are drop down list , text box and buttons when I pressed enter after text box it goes direct to buttons how can I stop that I didn't put that button as default button but I need to know why is that happening ?

Keep a Button control in the pressed state wp7?

How can I keep a Button control in the pressed state in a windows phone 7 app using C#? I want to have many different buttons on the screen, but when I press any of them I want it to stay pressed. Any ideas?
Also, once it is in its pressed state, is there a way to "depress" it manually?
Thanks

If the button properties are as follows:
foreground: white
background:black
Then in the pressing state its properties will be
foreground: black
background:white
If you change the properties of button in click event it can be seen as it is pressed. And making the IsEnabled property of button prevents it from firing the events on buttons.