c# - Selecting all contents of TextBox on clicking it -

i have 1 textbox. on clicking it, contents of textbox should selected. solution this? code have tried is:

<textbox name="questiontitle_textbox" text="question title" previewmousedown="questiontitle_textbox_previewmousedown"/> 

the function questiontitle_textbox_previewmousedown defined as

private void questiontitle_textbox_previewmousedown(object sender, system.windows.input.mousebuttoneventargs e) {         questiontitle_textbox.selectall(); } 

this works

<textbox name="questiontitle_textbox" text="question title" gotfocus="questiontitle_textbox_gotfocus" previewmouseleftbuttondown="questiontitle_textbox_previewmouseleftbuttondown"/> 

and in code behind

private void questiontitle_textbox_previewmouseleftbuttondown(object sender, mousebuttoneventargs e) {     textbox tb = (sender textbox);     if (tb != null)     {         if (!tb.isfocused)         {             e.handled = true;             tb.focus();         }     } }  private void questiontitle_textbox_gotfocus(object sender, routedeventargs e) {     textbox tb = (sender textbox);     if (tb != null)     {         tb.selectall();     } }