title: In ExtJS, event fired before clicking opening a file upload field
body: <p>I have <code>Ext.form.field.File</code>, with the <code>buttonOnly</code> attribute set to <code>true</code>. My question is, is there any event I can execute after I press the 'browse' button but before the file selector pops-up. I want the selector not to pop-up in certain conditions that I want to check. Any advice? I tried <code>show</code> and <code>keydown</code>. Both of which didn't execute.</p>