Templates

When working with HTML projects they often use template driven development. A small HTML stub is expanded on the server side with code generated by the server using a template mechanism. For example, for a photo list, the list header would be coded in HTML and the dynamic image list would be dynamically generated using a template mechanism. In general, this can also be done using QML but there are some issues with it.

First, it is not necessary. The reason HTML developers are doing this is to overcome limitations on the HTML backend. There is no component model yet in HTML so dynamic aspects have to be covered using these mechanisms or using programmatically javascript on the client side. Many JS frameworks are out there (jQuery, dojo, backbone, angular, …) to solve this issue and put more logic into the client-side browser to connect with a network service. The client would then just use a web-service API (e.g. serving JSON or XML data) to communicate with the server. This seems also the better approach for QML.

The second issue is the component cache from QML. When QML accesses a component it caches the render-tree and just loads the cached version for rendering. A modified version on disk or remote would not be detected without restarting the client. To overcome this issue we could use a trick. We could use URL fragments to load the URL (e.g. http://localhost:8080/main.qml#1234), where ‘#1234’ is the fragment. The HTTP server serves always the same document but QML would store this document using the full URL, including the fragment. Every time we would access this URL the fragment would need to change and the QML cache would not get a positive hit. A fragment could be for example the current time in milliseconds or a random number.

Loader {
    source: 'http://localhost:8080/main.qml#' + new Date().getTime()
}

In summary templating is possible but not really recommended and does not play to the strength of QML. A better approach is to use web-services which serve JSON or XML data.