UILongPressGestureRecognizer未调用其目标方法 [英] UILongPressGestureRecognizer not calling its target method

问题描述

此功能适用于iOS 11上的设备，但我的设备已更新至iOS 12不再有效：

This worked with devices on iOS 11, but with my device updated to iOS 12 it no longer works:

//the viewcontroller is initiated with UIGestureRecognizerDelegate

let longPressGesture = UILongPressGestureRecognizer(target: self, action: #selector(longPress))

//in cellForRowAt:
longPressGesture.minimumPressDuration = 1.0
longPressGesture.delegate = self
longPressGesture.cancelsTouchesInView = false
cell.addGestureRecognizer(longPressGesture)

@objc func longPress(longPressGestureRecognizer: UILongPressGestureRecognizer) {
     //never called
}

我也尝试将手势识别器添加到按钮，以确保它不是tableview的问题，并且longPress函数仍然没有被调用。

I also tried adding the gesture recognizer to a button in viewDidLoad to ensure it wasn't an issue with the tableview, and the longPress function is still not getting called.

推荐答案

//the viewcontroller is initiated with UIGestureRecognizerDelegate
let longPressGesture = UILongPressGestureRecognizer(target: self, action: #selector(longPress))

您似乎正在尝试将 longPressGesture 设置为UIViewController的实例属性，同时将其目标和操作作为其初始值设定项的一部分。那是行不通的，因为在初始化时，目标 self 不是实例。还没有实例；

It looks like you are trying to make longPressGesture an instance property of your UIViewController while giving it a target and action as part of its initializer. That's not going to work, because at the time it is initialized, the target, self, is not the instance. There is no instance yet; the instance is what we are in the middle of creating!

相反，将该行移动到 cellForRowAt：中，就像这样：

Instead, move that line into cellForRowAt:, like this:

//in cellForRowAt:
let longPressGesture = UILongPressGestureRecognizer(target: self, action: #selector(longPress))
longPressGesture.minimumPressDuration = 1.0
longPressGesture.delegate = self
longPressGesture.cancelsTouchesInView = false
cell.addGestureRecognizer(longPressGesture)

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