按钮单击事件直到完成为止不更新文本框

Question

Here's a C# code, What happens is when qsubmit button is clicked, program straight away displays "wait..!".

When I debug the program it is found that when I click and function executes textbox1.text = "Hello"; but doesn't updates textbox, it updates only when the control goes off the event function, when that happens value of textbox has already been changed to "wait..!" . I want to know why it doesn't updates textbox instantly(If that would have done, I would have seen the text during Thread.Sleep() )

 private void Button_QSubmit_Click(object sender, EventArgs e)
 {
      textBox1.Text = "Hello";
      Thread.Sleep(1000);
      textBox1.Text = "Wait..!";  
 }

Answer 1

You are hanging the UI Thread by calling Thread.Sleep from the Main Thread (UI), to update the text box you have to let the UI thread do its job outside your function to update the UI..anyway call Application.DoEvents() before the sleep. But calling Application.DoEvents() is a bad design

Answer 2

The UI thread is responsible to redraw the windows. So as long as you are doing this inside the UI Thread (eg a Button click event), the process is busy with your code and the window is not drawn.

A easy solution could be the use of an Timer. Just add an timer and in the button click you start it (eg you set itup to fire in 1 second).

The Timer Event then will simply set the Text.

https://msdn.microsoft.com/en-us/library/system.windows.forms.timer.aspx shows details about the Timer class.