ios - UISearchDisplayController 如何窃取 UISearchBar 事件

Question

我想实现一个类似 UISearchDisplayController 的 Controller 来显示搜索结果，并添加了一些日志来弄清楚逻辑。

看到日志后，我很好奇UISearchDisplayController是如何窃取UISearchBar事件的。

UISearchDisplayController 在不将 UISearchBarDelegate 设置为自身的情况下工作。而 UISearchBarDelegate 同时在外面工作!

以下是日志:

searchBarShouldBeginEditing:

searchBarTextDidBeginEditing:

searchDisplayControllerWillBeginSearch:

searchDisplayController:didLoadSearchResultsTableView:

searchBar:shouldChangeTextInRange:replacementText:

searchBar:textDidChange:

searchDisplayController:shouldReloadTableForSearchString:

searchDisplayController:willShowSearchResultsTableView:

searchDisplayController:didShowSearchResultsTableView:

searchBarCancelButtonClicked:

searchBarShouldEndEditing:

searchBarTextDidEndEditing:

searchDisplayController:willHideSearchResultsTableView:

searchDisplayController:didHideSearchResultsTableView:

searchBarShouldBeginEditing:

searchBarTextDidBeginEditing:

searchDisplayControllerWillBeginSearch:

searchBar:shouldChangeTextInRange:replacementText:

searchBar:textDidChange:

searchDisplayController:shouldReloadTableForSearchString:

searchDisplayController:willShowSearchResultsTableView:

searchDisplayController:didShowSearchResultsTableView:

searchBar:shouldChangeTextInRange:replacementText:

searchBarSearchButtonClicked:

searchBarShouldEndEditing:

searchBarTextDidEndEditing:

searchBarCancelButtonClicked:

searchDisplayController:willHideSearchResultsTableView:

searchDisplayController:didHideSearchResultsTableView:

Answer 1

好吧，我想通了。

您只需将 UISearchBar 委托(delegate)属性添加到 KVO 观察，然后将您的实现作为委托(delegate)代理即可做到这一点。

示例代码:

---

    if (searchBar.delegate) {
        self.searchBarDelegate = searchBar.delegate;
    }

    searchBar.delegate = self;

    [searchBar addObserver:self forKeyPath:@"delegate" options:NSKeyValueObservingOptionNew context:kSearchBarKVOContext];

---

#pragma mark - KVO
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if (context == kSearchBarKVOContext) {
        [self updateSearchBarDelegate];
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

---

- (void)updateSearchBarDelegate
{
    if (self.searchBar.delegate == self) {
        self.searchBarDelegate = nil;
    } else {
        self.searchBarDelegate = self.searchBar.delegate;
        self.searchBar.delegate = self;
    }
}

---

#pragma mark - NSObject Overrides
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
{
    NSMethodSignature *result = [super methodSignatureForSelector:aSelector];

    if (!result) {
        NSObject *obj = (NSObject *)self.searchBarDelegate;

        result = [obj methodSignatureForSelector:aSelector];
    }

    return result;
}

- (void)forwardInvocation:(NSInvocation *)anInvocation
{
    if ([self.searchBarDelegate respondsToSelector:[anInvocation selector]]) {
        [anInvocation invokeWithTarget:self.searchBarDelegate];
    } else {
        [super forwardInvocation:anInvocation];
    }
}

- (BOOL)respondsToSelector:(SEL)aSelector {
    return ([super respondsToSelector:aSelector] ||
            [self.searchBarDelegate respondsToSelector:aSelector]);
}