objective-c - CALayer 的动态可访问性标签

Question

如何使 CALayer 可访问？具体来说，我希望图层能够动态更改其标签，因为它可以随时更改。官方文档的示例代码并没有真正允许这样做。

Answer 1

以下假设您有一个超级视图，其层都是 class AccessableLayer，但如果您有更复杂的布局，则可以修改此方案以处理该问题。

为了使CALayer可访问，您需要一个实现UIAccessibilityContainer方法的父视图。这是执行此操作的一种建议方法。

首先，让每一层都有自己的UIAccessibilityElement

@interface AccessableLayer : CALayer 
@property (nonatomic) UIAccessibilityElement *accessibilityElement;
@end

现在在其实现中，您可以在元素更改时对其进行修改：

@implementation AccessableLayer

... self.accessibilityElement.accessibilityLabel = text;

@end

AccessableLayer 永远不会创建UIAccessibilityElement，因为构造函数需要 UIAccessibilityContainer。所以让超级视图创建并分配它：

#pragma mark - accessibility

// The container itself is not accessible, so return NO
- (BOOL)isAccessibilityElement
{
    return NO;
}

// The following methods are implementations of UIAccessibilityContainer protocol methods.
- (NSInteger)accessibilityElementCount
{
    return [self.layer.sublayers count];
}

- (id)accessibilityElementAtIndex:(NSInteger)index
{
    AccessableLayer *panel = [self.layer.sublayers objectAtIndex:index];
    UIAccessibilityElement *element = panel.accessibilityElement;
    if (element == nil) {
        element = [[UIAccessibilityElement alloc] initWithAccessibilityContainer:self];
        element.accessibilityFrame = [self convertRect:panel.frame toView:[UIApplication sharedApplication].keyWindow];
        element.accessibilityTraits = UIAccessibilityTraitButton;
        element.accessibilityHint = @"some hint";
        element.accessibilityLabel = @"some text";
        panel.accessibilityElement = element;
    }
    return element;
}

- (NSInteger)indexOfAccessibilityElement:(id)element
{
    int numElements = [self accessibilityElementCount];
    for (int i = 0; i < numElements; i++) {
        if (element == [self accessibilityElementAtIndex:i]) {
            return i;
        }
    }
    return NSNotFound;
}