ZK: Trigger upload button click by click on label

Introduction

This post is about how to trigger upload button's click by clicking on a label.
(Or, at least, looks like clicking on a label.)

The Program

trigger_button_click_by_click_label.zul

3 parts in this fragment, trigger by client side programming,
trigger by Clients.evalJavaScript from server side,
or triiger by real click on the invisible button

<zk xmlns:w="client">
    <!-- The style make upload button not visible
        instead of the red border -->
    <style>
        .z-button *,
        .z-upload * {
            background: transparent !important;
            margin: 0 !important;
            border: 0 !important;
            cursor: default !important;
        }
        .z-button-cm {
            display: none;
        }
        <!-- remove the red border below to make the
            upload button completely invisible -->
        .z-button {
            border: 1px solid red;
        }
    </style>
    <window>
        <!-- Click button by client side programming,
            override label's doClick_ function
            may not work in IE -->
        <label value="open upload dialog by client side programming">
            <attribute w:name="doClick_">
                function (evt) {
                    // call the original doClick_ function
                    this.$doClick_(evt);
                    //---- update domTarget and domEvent as need ----//
                    // evt.domEvent = THE_NEW_EVENT;                 //
                    // evt.domTarget = THE_NEW_TARGET;               //
                    //---- ------------------------------------- ----//
                    // click the upload button by JQuery
                    jq('$btn').next().find('input').click();
                }
            </attribute>
        </label>
        <div></div>
        <!-- Click button by Clients.evalJavascript
            may not work in some browsers -->
        <label value="open upload dialog by javascript that executed by server">
            <attribute name="onClick">
                Clients.evalJavaScript("jq('$btn').next().find('input').click();");
            </attribute>
        </label>
        <div></div>
        <!-- Click button directly
            the style of upload button is overridden
            to make it invisible, and will change position
            while mouseover one of the 3 labels below
            
            should work in most browsers -->
        <div style="position: relative; cursor: default;" height="30px"
            onMouseOver="uploadDiv.setParent(self);">
            <label value="open upload by real click on it" />
        </div>
        <div style="position: relative; cursor: default;" height="30px"
            onMouseOver="uploadDiv.setParent(self);">
            <label value="also open upload by real click on it" />
        </div>
        <div style="position: relative; cursor: default;" height="30px"
            onMouseOver="uploadDiv.setParent(self);">
            <label value="still open upload by real click on it" />
        </div>
        result: <label id="result" />
        <div style="position: relative;">
            <div id="uploadDiv" style="position: absolute; left: 0px; top: 0px; z-index: 100;">
                <button id="btn" label="Upload" upload="true"
                    width="200px" height="15px">
                    <attribute name="onUpload"><![CDATA[
                        import org.zkoss.util.media.Media;
                        Media[] media = event.getMedias();
                        if (media != null) { // show the infprmation of updated media
                            StringBuilder sb = new StringBuilder("");
                            for (int i = 0; i < media.length; i++) {
                                sb.append(media[i].getName() + ", "+media[i].getByteData().length +" bytes\n");
                            }
                            result.setValue(sb.toString());
                        }
                        ]]></attribute>
                </button>
            </div>
        </div>
    </window>
</zk>

The Result

view demo flash on line:
http://screencast.com/t/HIXvMRjMGhrb

download it:
https://github.com/benbai123/ZK_Practice/blob/master/Components/demos/trigger_button_click_by_click_label.swf?raw=true

Download

trigger_button_click_by_click_label.zul
https://github.com/benbai123/ZK_Practice/blob/master/Components/projects/Components_Practice/WebContent/trigger_button_click_by_click_label.zul