On button click Change Text of button in CollapsiblePanelextender

I've a panel with button tied up to collapsiblepanelextender.when I click on the button with text "Click" the collapsepanel expands and my button text needs to be changed as "Cancel" and when clicked cancel the panel collapses and button again changed to "Click".I've my below code.It's changing the button text to "Cancel" when the panel expands but not reverting back to "Click" text.

protected void Button1_Click(object sender, EventArgs e) { if (IsPostBack) { Button1.Text = "Cancel"; }




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