How do I send text to an active window when I click a button on a WPF window using C#?

Question

I'm building an On-Screen keyboard using WPF and C# and I would like to know how to tell my program to enter text in an active window when I click a button. I want it to behave like other on-screen keyboards.

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Answer 1

One way could be the use of a Messenger, like it's a common use in MVVM-Patterns.

You can register a Method to the messenger:

messengerInstance.Register<objecttype>(object recipient, string identCode, Action<objecttype> method);

And you can send a message like this:

messengerInstance.Send<objecttype>(object obj, string identCode);

So for example you have a Method MyMethod(string str). Then you can register it with

messengerInstance.Register<string>(this /*you are referring to this instance*/, "MyCode", MyMethod);

Now you send a message in another class:

messengerInstance.Send<string>("A", "MyCode");

What happens now, is that every Method, that is registered to the Code "MyCode" gets "A" as parameter and gets executed.

Bigger example:

public class A
{
    private Messenger messenger = Messenger.Instance; //Messenger is singleton, means it is build to only have one instance

    public A()
    {
        messenger.Register<string>(this, "MyCode", MyMethod);
    }

    private void MyMethod(string str)
    {
        Console.WriteLine(str);
    }
}

public class B
{
    private Messenger messenger = Messenger.Instance;

    public B()
    {
        messenger.Send<string>("Hello, World!", "MyCode");
    }
}

When class B gets initialized, the constructor sends the message "Hello, World!" with the IdentCode "MyCode". Now class A gets the notification "I have the message Hello, World! for everyone who is registered to MyCode". Class A sees that MyMethod is registered to this code and passes the message "Hello, World!" to the Method. In the end you get the output "Hello, World!"

Of course this is simplified, there are plenty of possibilities to create such a messenger, this is just my version that I use, but it's quite without stress, you can basically send the letters to the textbox. Of course you can send any object you like. For example

//an integer
messenger.Send<int>(10, "MyCode");

//a boolean
messenger.Send<bool>(true, "MyCode");

//or even other classes
messenger.Send<MyClass>(new MyClass(), "MyCode");

This is my Messenger-class I use at work: https://pastebin.com/k6q9Y6rR

Answer 2

Is your button subscribed to some sort of click event? If it is, you can just add the value the button has to the active window you're talking about by concatenating the button string value to the current value in your active window. If there's no click event, you can add one and then do as i mentionned above

how to subscribe to a button click event:

btn.Click += btn1_Click;

private void btn1_Click(object sender, RoutedEventArgs e)
{
    // concatenate to the active window result view the button value here
}