January 2020
Intermediate to advanced
356 pages
6h 4m
Chinese
Content preview from Swift游戏开发经典实例
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96
｜
第
3
章
UIPinchGestureRecognizer
的核心属性是
Scale
。手势开始时，
Scale
的初始值是
1
，
如果手指间距离正在靠近（捏合手势），则这个值会无限趋近于
0
，如果手指间距
离正在扩大（捏放手势），则这个值会从
1
开始不断增大。
Scale
的值是相对于初
始值的，例如，如果用户手指做放大动作，直到
Scale
值变为
2
，然后又做捏合手势，
那么从捏合手势一开始的那一刻起，
Scale
就被重设为
1
。
要想验证这个，你可以把下面这行代码注释掉试试：
pinchGesture.scale = 1.0
3.6
自定义手势
问题
如何为自定义手势创建一个手势识别器？
解决方案
要创建新的手势识别器需要子类化
UIGestureRecognizer
。首先，我们创建一个新
的类，让它继承自
UIGestureRecognizer
。
在本例中，我们创建了一个新手势识别器，用于识别手指先向下移动然后又向上移
动，然后抬起的动作。如图
3-1
所示。当然，无论是创建多简单还是多复杂的手势
都是可以的。
图
3
-
1
：先向下划然后又向上划的手势
在这个例子中，新的
UIGestureRecognizer
子类命名为
DownUpGestureRecognizer
。
新建一个文件
DownUpGestureRecognizer
.swift
，然后加入如下代码：
输入
｜
97
import UIKit.UIGestureRecognizerSubclass
class DownUpGestureRecognizer: UIGestureRecognizer ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.