Question: When I use different layouts to support different screens , should I use dp or px .

Answer: 
```
$(".fold_reply").click(function() {
    $(".reply").toggle(500)
}

```

Toggle will show or hide the element depending on its current state, eliminating your if block.

Check this fiddle out for an example:

<http://jsfiddle.net/z9rGz/3/>
Use the jQueryUI version of `toggle()` since you seem to be using a jQuery UI effect

**.toggle( effect [, options ] [, duration ] [, complete ] )**

Reference: <http://api.jqueryui.com/toggle/>

```
$(".fold_reply").click(function() {
     $(".reply").toggle("fold",  500);
})

```