在 UITableView 中观察捏合多点触控手势

Question

我希望在 UITableView 上实现捏合/拉出，我已经研究了几种方法，包括这个：

Similar question

但是，虽然我可以创建一个 UIViewTouch 对象并将其覆盖到我的 UITableView 上，但滚动事件不会被中继到我的 UITableView，我仍然可以选择单元格，并且它们会通过触发到新 ViewController 对象的转换来正确响应。但是，尽管传递了 touchesBegan、touchesMoved 和 touchesEnded 事件，但我无法滚动 UITableView。

Answer 1

这似乎是一个经典问题。就我而言，我想通过 UIWebView 拦截一些不能被子类化的事件，等等。

我发现最好的方法是使用 UIWindow 拦截事件：

EventInterceptWindow.h

@protocol EventInterceptWindowDelegate
- (BOOL)interceptEvent:(UIEvent *)event; // return YES if event handled
@end


@interface EventInterceptWindow : UIWindow {
    // It would appear that using the variable name 'delegate' in any UI Kit
    // subclass is a really bad idea because it can occlude the same name in a
    // superclass and silently break things like autorotation.
    id <EventInterceptWindowDelegate> eventInterceptDelegate;
}

@property(nonatomic, assign)
    id <EventInterceptWindowDelegate> eventInterceptDelegate;

@end

EventInterceptWindow.m：

#import "EventInterceptWindow.h"

@implementation EventInterceptWindow

@synthesize eventInterceptDelegate;

- (void)sendEvent:(UIEvent *)event {
    if ([eventInterceptDelegate interceptEvent:event] == NO)
        [super sendEvent:event];
}

@end

创建该类，将 MainWindow.xib 中的 UIWindow 类更改为 EventInterceptWindow，然后在某处将 eventInterceptDelegate 设置为要拦截事件的视图控制器。拦截双击的示例：

- (BOOL)interceptEvent:(UIEvent *)event {
    NSSet *touches = [event allTouches];
    UITouch *oneTouch = [touches anyObject];
    UIView *touchView = [oneTouch view];
    //  NSLog(@"tap count = %d", [oneTouch tapCount]);
    // check for taps on the web view which really end up being dispatched to
    // a scroll view
    if (touchView && [touchView isDescendantOfView:webView]
            && touches && oneTouch.phase == UITouchPhaseBegan) {
        if ([oneTouch tapCount] == 2) {
            [self toggleScreenDecorations];
            return YES;
        }
    }   
    return NO;
}

这里的相关信息： http://iphoneincubator.com/blog/windows-views/360idev-iphone-developers-conference-presentation

Answer 2

尼姆罗德写道：

在某处将 eventInterceptDelegate 设置为要拦截事件的视图控制器

我没有立即理解这句话。为了其他和我有同样问题的人的利益，我这样做的方法是将以下代码添加到我的 UIView 子类中，该子类必须检测触摸。

- (void) viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    // Register to receive touch events
    MyApplicationAppDelegate *appDelegate = (MyApplicationAppDelegate *) [[UIApplication sharedApplication] delegate];
    EventInterceptWindow *window = (EventInterceptWindow *) appDelegate.window;
    window.eventInterceptDelegate = self;
}


- (void) viewWillDisappear:(BOOL) animated
{
    // Deregister from receiving touch events
    MyApplicationAppDelegate *appDelegate = (MyApplicationAppDelegate *) [[UIApplication sharedApplication] delegate];
    EventInterceptWindow *window = (EventInterceptWindow *) appDelegate.window;
    window.eventInterceptDelegate = nil;

    [super viewWillDisappear:animated];
}


- (BOOL) interceptEvent:(UIEvent *) event
{
    NSLog(@"interceptEvent is being called...");
    return NO;
}

这个版本的interceptEvent: 是捏到缩放检测的简单实现。注意。部分代码取自 Apress 的《开始 iPhone 3 开发》。

CGFloat initialDistance;

- (BOOL) interceptEvent:(UIEvent *) event
{
    NSSet *touches = [event allTouches];

    // Give up if user wasn't using two fingers
    if([touches count] != 2) return NO;

    UITouchPhase phase = ((UITouch *) [touches anyObject]).phase;
    CGPoint firstPoint = [[[touches allObjects] objectAtIndex:0] locationInView:self.view];
    CGPoint secondPoint = [[[touches allObjects] objectAtIndex:1] locationInView:self.view];

    CGFloat deltaX = secondPoint.x - firstPoint.x;
    CGFloat deltaY = secondPoint.y - firstPoint.y;
    CGFloat distance = sqrt(deltaX*deltaX + deltaY*deltaY);

    if(phase == UITouchPhaseBegan)
    {
        initialDistance = distance;
    }
    else if(phase == UITouchPhaseMoved)
    {
        CGFloat currentDistance = distance;
        if(initialDistance == 0) initialDistance = currentDistance;
        else if(currentDistance - initialDistance > kMinimumPinchDelta) NSLog(@"Zoom in");
        else if(initialDistance - currentDistance > kMinimumPinchDelta) NSLog(@"Zoom out");
    }
    else if(phase == UITouchPhaseEnded)
    {
        initialDistance = 0;
    }

    return YES;
}

编辑：虽然这段代码在 iPhone 模拟器中 100% 运行良好，但当我在 iPhone 设备上运行它时，我遇到了与表格滚动相关的奇怪错误。如果您也遇到这种情况，请强制 interceptEvent: 方法在所有情况下都返回 NO。这意味着超类也会处理触摸事件，但幸运的是这并没有破坏我的代码。