Archive for the ‘custom controls’ Category
Create a custom headerRender for the AdvancedDataGrid column with a checkbox control embeded and adhering to the following functional requirements
- support(retain) the column sort functionality
- must be a reusable component (no tight coupling)
- easy to extend and plugin to use in any other grid control
Provide the Select All rowItems functionality for the grid column. Each row item will have a checkbox to allow its (un)selection.
The Select All functionality for all the row items in the grid is a very common requirement for any application, but however before implementing we need to be clear about the dataProvider as well.
Will the dataProvider for the grid have dataFields, which can be binded to the state of the checkbox in the column header and for each of the row items?
If the dataProvider contains dataFields which can be binded to the UI it is fairly simple to handle the use case, but if the SelectAll is purely a UI operation for populating the list of selected items for further processing, then it becomes little more challenging.
One more challenge here is to preserve the sort functionality for the column, as any custom implementation of the headerRenderer or any component being used as the headerRenderer will strip off the sort functionality for the column. Check it out for yourself if you dont believe it.
Here is the approach that I followed to address the constraint on
>ReUsability: Program to an interface and avoid tight coupling with the parentDocument while handling the communication and binding with the grid.
>Extensibility: Encapsulate the behaviour in the class as a separate .as file extending UIComponent and provide the customizable behaviour in the virtual methods which cane be overriden if required by the derived classes.
There are two approaches to implement the checkbox headerRenderer
Appraoch 1: Specify any implementation of UIComponent (say CustomCheckbox) as a headerRenderer for the grid column
But then you need to be prepared to handle the layout and rendering of the sortItemRenderer inorder to provide the sort functionality on the column. Also you need to be prepared to hook onto the instance of the headerRenderer for communication with the grid as you will be stumped to discover that the grid creates a new instance of the headerRenderer every now and then. Possible work around for this is to create the instance of the headerRenderer as an instance of the classFactory and store it as a bindable value in the parentDocument. After managing all of it you still need to be able to differentiate between a click to Sort and click to SelectAll by putting in vague logic based on the position of mouse click. I hope you agree that it cant get simpler than this 🙂
Approach 2: Implement the custom headerRenderer by extending the default AdvancedDataGridHeaderRender implementation and specify it in the grid column
This approach looks the obvious natural choice but then you need to know how and where to insert the custom implementation. Refer to my post on creating custom Flex controls for more info on it. Also you need to be able to differentiate between a click to Sort and click to SelectAll, which I managed it by controling the sort property of the column in response to mouse hover 😉 . Look below for the OnMouseRollOver method.
Show me the source code: Continue reading
commitProperties(): Update/Bind the properties of the child controls in the custom control here. This is the last method to be called before rendering, hence it is a good place to update the properties of the child controls to acheive the binding . More Info
We would not require to make an explict call to any of the methods above as they are called by the Flex framework itself, we only need to plugin in the custom code in the invocation sequence appropriately. Refer to the link “More Info” for a comprehensive documentation of the usage of the methods.
We may not need to override all of them, but it is important to know the appropriate method to be overriden. Also do not forget to call the implementation of the base class unless you are really sure to do so.