如何使用按钮在文本框中添加和插入文本

我正在为我的项目编程一个虚拟键盘.在按钮A上，我写的代码为

Hi,

I am programming a virtual keyboard for my project. On a button A, i written a code as

Private Sub Button19_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btna.Click
        txtpatname.Text = txtpatname.Text.Insert(txtpatname.SelectionStart, "a")
End Sub

使用此代码，每次我必须选择文本框然后单击按钮A时(即不附加按钮)，它将直接在文本框的开头显示光标.

任何帮助将不胜感激.

在此先谢谢您.

With this code, everytime I have to select textbox and then click on Button A i.e it not appending, it is showing cursor directly at start of the textbox.

Any help will be kindly appreciated.

Thanks in advance.