拾取和弹出力触摸手势有时不起作用

Question

我有一个视图控制器，它在viewDidLoad方法中注册预览：

- (void) viewDidLoad
{
    [super viewDidLoad];
    if ([self.traitCollection respondsToSelector:@selector(forceTouchCapability)] &&
        (self.traitCollection.forceTouchCapability == UIForceTouchCapabilityAvailable))
    {
        [self registerForPreviewingWithDelegate:self sourceView:self.view];
    }
}

但有时无法识别强制触摸，就好像视图控制器没有注册预览一样。

Answer 1

从状态恢复启动应用程序时出现问题。修复：在视图中放置预览注册代码WillAppear:

- (void) viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    if ([self.traitCollection respondsToSelector:@selector(forceTouchCapability)] &&
        (self.traitCollection.forceTouchCapability == UIForceTouchCapabilityAvailable))
    {
        [self registerForPreviewingWithDelegate:self sourceView:self.view];
    }
}

当从状态恢复调用viewDidLoad时，注册预览的时机正合适。