Issues with keyboard navigation on list with custom renderer

问题

We have a list that uses a custom renderer containing a label, a checkbox and two icons (which have click events). This list needs to be made WCAG 2.0 compliant and in order to do that we need the list to be keyboard navigable.

The problem is with being able to move from one list item to the next and have the focus move to the label for the next/previous list item. Specifically, when the user enters the list using TAB button, the label for the first list item receives focus (highlighted box around text) and the entire row in the list is highlighted as the selected item.

However, when the user then presses the down arrow key to move to the next list item, the next row becomes highlighted (is now the selected item) but the focus remains on the label of the previous row (highlight still shown around label for row 1). The only way to get the focus to move to the newly selected row is to tab through the checkbox and two icons. This isn't a big deal if there are only a couple list items but would be a pain if there are 20+ rows in the list.

Is there a way to get the focus to move to the label of the newly selected row as soon as the user moves (using up/down cursor keys) to the new list item? I know a picture would help but I don't have anyway of posting a screenshot online. Any help would be greatly appreciated.

回答1:

You're going to have to dig into how focus works in Flex. This is not a complete answer, but hopefully you can put together a solution that works for you. I did this about 4-5 years ago in Flex 3, but it should be similar in Flex 4.

How Focus Works in Flex

The main things to know are the FocusManager singleton class and the IFocusManagerComponent interface.

The FocusManager moves the focus around the UI based on user interactions (mouse clicks, keyboard navigation, etc.).

If a component implements the IFocusManagerComponent interface, then the FocusManager will include it in the "tab" loop and allow the component to be focused via keyboard navigation.

How Focus Works With Flex List Components

You've already stumbled onto the peculiarities of how focus works with the List component and item renderers. The Flex List components implement IFocusMangerComponent and so when you tab through the UI the FocusManager sends the focus to the list.

The List may or may not focus the item renderers. In Flex 3 you had to be using editable item renderers for this to happen, it may or may not be the same in Flex 4.

Some Ideas for Solutions to Your Problem

I think there are numerous ways to solve this. Use some combination of these techniques:

• override the protected keyDownHandler() method of the List component. I don't have the code handy, but if you look at it's implementation in the List class you should be able to make your overridden version set the focus on the next renderer.

• use methods of the FocusManager to find components in the tab loop: getNextFocusManagerComponent(), findFocusManagerComponent(). Check the docs there are others that will be useful. For example, when the user presses the down arrow, you can let the next item renderer get selected, then use findFocusManagerComponent() (passing in the newly selected renderer) and then tell the FocusManager to focus it with the setFocus() method. This is probably not exactly the right approach ;)

• By the way, the FocusManger is a Flex singleton object, every UIComponent in Flex has a focusManager property you can use to get a reference to it.

• consider disabling focus on objects that don't need to receive focus (like the Label in your item renderer). There are numerous properties to do this: focusEnabled, hasFocusableChildren, mouseFocusEnabled, tabEnabled, tabChildren etc.

• consider disabling focus on the List component, but then making your item renderers implement the IFocusManagerComponent interface. Implementing the interface is simple, you just declare it in your class (there's no actual methods to implement). The tricky part will be now your item renderers need to have key down handlers (just override the protected keyDownHandler() method that all UIComponent objects have).

I think there are other techniques you can use, it's just been too long since I did this. I'd be happy to provide more help if you get stuck somehwere...

来源：https://stackoverflow.com/questions/18924620/issues-with-keyboard-navigation-on-list-with-custom-renderer