Swift版PhotoStackView——照片叠放视图
浏览数：38 /
时间：2015年06月08日
前言
之前流行过一种图片展示视图——photo stack，即照片叠放视图。大致上是这个样子的：
（图片出自code4app）
现在我们已经能够使用UICollectionViewLayout来实现这种视图了。Apple给的示例代码中就有这样一个layout，并且示例代码中不仅仅是展示这样的视图，还有非常棒的layout过度动画（结合手势）。在这之前，也有非常多的开源代码能实现这样的效果。本文正是借鉴了开源的源代码“PhotoStackView”,使用Objective-C实现，并且带手势移动图片的功能。由于这是上一学期课设的时候拿来用的库，结果现在找不到了，无法给出链接，还望见谅。
最后的效果图如下
移动、添加与删除
下一张
这样重复造轮子的目的是什么呢？一方面，不使用UICollectionViewLayout而是纯粹的用UIView来实现，提高灵活性，方便“私人订制”。另一方面，学习大神的源代码，从中学习一下自定义库的书写方式等。最后，swift。。天杀的swift，是谁说swift对新手友好来着
当然，这里也不是简单的对源代码的搬运、抄袭与翻译，我还根据自己的需要给他改了一个bug，添加了一些功能，比如全屏展示与返回等。示例图如下：
- 全屏展示
（图片有些卡，测试运行时还是非常流畅的）
思路
- 使用若干和自己一样大的view来装载图片，每次添加新图片到视图上时为其随机旋转一定角度，把最前面的这张旋转角度设为0。
- “view装载图片”的意思是，view里面放一个imageView，为什么不直接用imageVIew呢？因为我们要放边框，边框可以是图片，另外在highlighted状态下也可以用图片或自定义颜色铺在图片上，因此使用一个view统一管理
- 添加pan手势，当手指移动时让view跟着做相应平移，手指松开时根据velocity决定返回还是移到最后
- 综上，我们还需要不少辅助方法，例如获取顶部图片和其下标、使用动画移动view、让view旋转到某一度数等
代码
computed property & stored property
oc中可以声明属性然后覆写setter或getter，从而实现赋值或取值时进行一些操作的功能，如下代码
@property(strong, nonatomic) NSString *someString
- (void)setSomeString() {...}
- (NSString *)someString() {...}swift中相对应的写法，目前我知道的有两种，一种是使用computed property 的set和get，缺点是必须同时声明一个stored property（？可以不用吗，求科普），很像oc2.0之前的属性。另一种是使用监听器（didSet和willSet），缺点是只能对setter操作，不能对getter操作。
但是，要想实现重写父类的setSomeThing这样的功能，只能通过监听器的方法。否则会报错
由上，该类用到的属性如下（部分）：
//MARK: computed property
var s_rotationOffset: CGFloat = 0.0
/// the scope of offset of rotation on every photo except the first one. default is 4.0.
/// ie, 4.0 means rotate iamge with degree between (-4.0, 4.0)
var rotationOffset: CGFloat {
set {
if s_rotationOffset == newValue {
return
}
s_rotationOffset = newValue
reloadData()
}
get {
return s_rotationOffset
}
}
var s_photoImages: [UIView]?
var photoImages: [UIView]? {
set {
//remove all subview and prepare to re-add all images from data source
for view in subviews {
view.removeFromSuperview()
}
if let images = newValue {
for view in images {
//keep the original transfrom for the existing images
if let index = find(images, view), count = s_photoImages?.count where index < count {
let existingView = s_photoImages![index]
view.transform = existingView.transform
} else {
makeCrooked(view, animated: false)
}
insertSubview(view, atIndex: 0)
}
}
s_photoImages = newValue
}
get {
return s_photoImages
}
}
override var highlighted: Bool {
didSet {
let photo = self.topPhoto()?.subviews.last as! UIImageView
if highlighted {
let view = UIView(frame: self.bounds)
view.backgroundColor = self.highlightColor
photo.addSubview(view)
photo.bringSubviewToFront(view)
} else {
photo.subviews.last?.removeFromSuperview()
}
}
}
override var frame: CGRect {
didSet {
if CGRectEqualToRect(oldValue, self.frame) {
return
}
reloadData()
}
}
上面大部分还有其他省略的大都是一样的思路：设置新值时调用reloadData刷新，主要是上面那个photoImage数组的setter：首先移除当前所有的子视图，接下来遍历新数组，那句判断if let index = find(images, view), count = s_photoImages?.count where index < count的作用是判断此次循环中view是否是之前已经添加到界面上的，如果是，则保留其transform不变，否则为其重新生产一个旋转角度（产生照片堆效果），这样做保证了添加照片时原先的照片形状不会变。
Set up & Touches
初始化的工作非常简单，一方面为属性设置默认值，另一方面添加手势监听。
//MARK: Set up
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setup()
}
func setup() {
//default value
borderWidth = 5.0
showBorder = true
rotationOffset = 4.0
let panGR = UIPanGestureRecognizer(target: self, action: Selector("handlePan:"))
addGestureRecognizer(panGR)
let tapGR = UITapGestureRecognizer(target: self, action: Selector("handleTap:"))
addGestureRecognizer(tapGR)
reloadData()
}
override func sendActionsForControlEvents(controlEvents: UIControlEvents) {
super.sendActionsForControlEvents(controlEvents)
highlighted = (controlEvents == .TouchDown)
}sendActionsForControlEvents是自定义UIControl时可能会使用或重写的方法，作用是发送事件。为了说明这一点，这里顺带附上view的触摸方法：
//MARK: Touch Methods
override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
super.touchesBegan(touches, withEvent: event)
sendActionsForControlEvents(.TouchDown)
}
override func touchesMoved(touches: Set<NSObject>, withEvent event: UIEvent) {
super.touchesMoved(touches, withEvent: event)
sendActionsForControlEvents(.TouchDragInside)
}
override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent) {
super.touchesEnded(touches, withEvent: event)
sendActionsForControlEvents(.TouchCancel)
}例如，当用户点击该控件时，发送UIControlEventTouchDown事件，这样使用该控件的人就可以通过addTarget:selector:forControlEvent:方法对此事件添加监听了。我们平时最经常使用的button不就是对TouchUpInside事件进行监听的吗。
reloadData
刷新视图时，要做的事情有：重新获取size，计算frame，添加border，设置images
/**
use this method to reload photo stack view when data has changed
*/
func reloadData() {
if dataSource == nil {
photoImages = nil
return
}
if let number = dataSource?.numberOfPhotosInStackView(self) {
var images = [UIView]()
let border = borderImage?.resizableImageWithCapInsets(UIEdgeInsets(top: borderWidth, left: borderWidth, bottom: borderWidth, right: borderWidth))
let topIndex = indexOfTopPhoto()
for i in 0..<number {
if let image = dataSource?.stackView(self, imageAtIndex: i) {
//add image view for every image
let imageView = UIImageView(image: image)
var viewFrame = CGRectMake(0, 0, image.size.width, image.size.height)
if let ds = dataSource where ds.respondsToSelector(Selector("stackView:sizeOfPhotoAtIndex:")) {
let size = ds.stackView!(self, sizeOfPhotoAtIndex: i)
viewFrame.size = size
}
imageView.frame = viewFrame
let view = UIView(frame: viewFrame)
//add border for view
if showBorder {
if let b = border {
viewFrame.origin = CGPoint(x: borderWidth, y: borderWidth)
imageView.frame = viewFrame
view.frame = CGRect(x: 0, y: 0, width: imageView.frame.width + 2 * borderWidth, height: imageView.frame.height + 2 * borderWidth)
let backgroundImage = UIImageView(image: b)
backgroundImage.frame = view.frame
view.addSubview(backgroundImage)
} else {
view.layer.borderWidth = borderWidth
view.layer.borderColor = UIColor.whiteColor().CGColor
}
}
view.addSubview(imageView)
//add view to array
images.append(view)
view.tag = i
view.center = CGPoint(x: CGRectGetMidX(bounds), y: CGRectGetMidY(bounds))
}
}
photoImages = images
goToImageAtIndex(topIndex)
}
}这里要干的仅有前三件事，添加photos的任务交给photoImages的setter去做，这个之前已经说过了。
逻辑相关
在谈这个之前，让我们先来了解一下view的组织方式。如果一个view内有若干个subview，你知道subviews.lastObject和subviews.firstObject分别指哪个吗？
事实上，越是靠近我们的，下标识越小。换句话说，subviews[0]指的是子视图中位于最底层的，被其他子视图遮住了的那一个，而subviews.lastObject指的则是最顶层的，能被我们看到（一般来说）的。
这样，很容易能得出下面几个函数
/**
find the index of top photo
:returns: index of top photo
*/
func indexOfTopPhoto() -> Int {
if let images = photoImages, let photo = topPhoto() {
if let index = find(images, photo) {
return index
}
}
return 0
}
/**
get the top photo on photo stack
:returns: current first photo
*/
func topPhoto() -> UIView? {
if subviews.count == 0 {
return nil
}
return subviews[subviews.count - 1] as? UIView
}
/**
jump to photo at index
*/
func goToImageAtIndex(index: Int) {
if let photos = photoImages {
for view in photos {
if let idx = find(photos, view) where idx < index {
sendSubviewToBack(view)
}
}
}
makeStraight(topPhoto()!, animated: false)
}swift知识补充：swift中没有indexForObject:这样的方法，众所周知，swift更多的是“函数式编程”，因此Int、Float甚至Array、Dictionary都是结构体（虽然和类挺相似），我们也是使用一些函数来对这些结构体操作。例如这里取代上述方法的是find()函数
有了这些方法，我们就能使用动画后处理view的层级关系了。
动画相关
这里用到的动画相关的都非常简单，所以直接上代码：
//MARK: Animations
func returnToCenter(view: UIView) {
UIView.animateWithDuration(0.2, animations: { () -> Void in
view.center = CGPoint(x: CGRectGetMidX(self.bounds), y: CGRectGetMidY(self.bounds))
})
}
func flickAway(view: UIView, withVelocity velocity: CGPoint) {
if let del = delegate where del.respondsToSelector(Selector("stackView:willFlickAwayPhotoFromIndex:toIndex:")) {
let from = indexOfTopPhoto()
var to = from + 1
if let number = dataSource?.numberOfPhotosInStackView(self) where to >= number {
to = 0
}
del.stackView!(self, willFlickAwayPhotoFromIndex: from, toIndex: to)
}
let width = CGRectGetWidth(bounds)
let height = CGRectGetHeight(bounds)
var xPosition: CGFloat = CGRectGetMidX(bounds)
var yPosition: CGFloat = CGRectGetMidY(bounds)
if velocity.x > 0 {
xPosition = CGRectGetMidX(bounds) + width
} else if velocity.x < 0 {
xPosition = CGRectGetMidX(bounds) - width
}
if velocity.y > 0 {
yPosition = CGRectGetMidY(bounds) + height
} else if velocity.y < 0 {
yPosition = CGRectGetMidY(bounds) - height
}
UIView.animateWithDuration(0.1, animations: { () -> Void in
view.center = CGPoint(x: xPosition, y: yPosition)
}) { (finished) -> Void in
self.makeCrooked(view, animated: true)
self.sendSubviewToBack(view)
self.makeStraight(self.topPhoto()!, animated: true)
self .returnToCenter(view)
if let del = self.delegate where del.respondsToSelector("stackView:didRevealPhotoAtIndex:") {
del.stackView!(self, didRevealPhotoAtIndex:self.indexOfTopPhoto())
}
}
}
func rotate(degree: Int, onView view: UIView, animated: Bool) {
let radian = CGFloat(degree) * CGFloat(M_PI) / 180
if animated {
UIView.animateWithDuration(0.2, animations: { () -> Void in
view.transform = CGAffineTransformMakeRotation(radian)
})
} else {
view.transform = CGAffineTransformMakeRotation(radian)
}
}
func makeCrooked(view: UIView, animated: Bool) {
let min = Int(-rotationOffset)
let max = Int(rotationOffset)
let scope = UInt32(max - min - 1)
let randomDegree = Int(arc4random_uniform(scope))
let degree: Int = min + randomDegree
rotate(degree, onView: view, animated: animated)
}
func makeStraight(view: UIView, animated: Bool) {
rotate(0, onView: view, animated: animated)
}swift相关：一直不是太明白swift中可选值的意义是什么。到是给我们带来了不少麻烦，因为不怎么想全都用强解(!)，所以用了大量if let解包的方式。其中oc中很简单就能完成的操作：
if (self.delegate responseToSelector:@selector(@"someMethod")) {
[self.delegate someMethod];
}到了swift中
if let del = delegate where del.responseToSelector(Selector("someMethod") {
del.someMethod()
}且不说swift的Selector机制，每次都这样写可真是要累死人了:[
手势
和之前说的一样，pan手势中要做的就是通知代理，让view随手指移动，释放手指后根据velocity将view归位或切换到最后一张。
//MARK: Gesture Recognizer
func handlePan(recognizer: UIPanGestureRecognizer) {
if let topPhoto = self.topPhoto() {
let velocity = recognizer.velocityInView(recognizer.view)
let translation = recognizer.translationInView(recognizer.view!)
if recognizer.state == .Began {
sendActionsForControlEvents(.TouchCancel)
if let del = delegate where del.respondsToSelector(Selector("stackView:willBeginDraggingPhotoAtIndex")) {
del.stackView!(self, willBeginDraggingPhotoAtIndex: self.indexOfTopPhoto())
}
} else if recognizer.state == .Changed {
topPhoto.center = CGPoint(x: topPhoto.center.x + translation.x, y: topPhoto.center.y + translation.y)
recognizer.setTranslation(CGPoint.zeroPoint, inView: recognizer.view)
} else if recognizer.state == .Ended || recognizer.state == .Cancelled {
if abs(velocity.x) > 200 {
flickAway(topPhoto, withVelocity: velocity)
} else {
returnToCenter(topPhoto)
}
}
}
}
func handleTap(recognizer: UIGestureRecognizer) {
sendActionsForControlEvents(.TouchUpInside)
if let del = delegate where del.respondsToSelector(Selector("stackView:didSelectPhotoAtIndex:")) {
del.stackView!(self, didSelectPhotoAtIndex: self.indexOfTopPhoto())
}
}Show All Images
创建一层黑色的遮罩（view），然后将每个view从自己原来的位置移到计算好的新位置，为了产生顺序关系，为每个view 的动画设置各自的delay。点击黑色遮罩后所有view回位，view消失。
func showAllPhotos() {
let screenBounds = UIScreen.mainScreen().bounds
let maskView = UIView(frame: screenBounds)
maskView.backgroundColor = UIColor.blackColor()
maskView.alpha = 0
UIApplication.sharedApplication().keyWindow?.addSubview(maskView)
UIView.animateWithDuration(0.1, delay: 0.0, options: nil, animations: { () -> Void in
maskView.alpha = 1.0
}) { (_) -> Void in
}
let column = 3
let imageWidth = 80
let padding = (Int(screenBounds.width) - column * imageWidth) / (column + 1)
if let photos = photoImages {
for view in photos {
//set the initial location
view.removeFromSuperview()
maskView.addSubview(view)
view.frame = frame
if let index = find(photos, view) {
UIView.animateWithDuration(0.1, delay: NSTimeInterval(Double(index) * 0.1), options: nil, animations: { () -> Void in
view.frame = CGRect(x: padding + (index % column) * (imageWidth + padding), y: padding + (index / column) * (padding + imageWidth), width: imageWidth, height: imageWidth)
}, completion: { (finished) -> Void in
})
}
}
}
let tapGR = UITapGestureRecognizer(target: self, action: Selector("removeMaskView:"))
maskView.addGestureRecognizer(tapGR)
} func removeMaskView(recognizer: UITapGestureRecognizer) {
let maskView = recognizer.view!
for i in stride(from: maskView.subviews.count - 1, through: 0, by: -1) {
let photo = maskView.subviews[i] as? UIView
UIView.animateWithDuration(0.25, animations: { () -> Void in
photo?.frame = self.frame
}, completion: { (_) -> Void in
})
}
UIView.animateWithDuration(0.25, animations: { () -> Void in
maskView.alpha = 0.0
}) { (_) -> Void in
maskView.removeFromSuperview()
self.reloadData()
}
}源代码
本文的源代码可以从这里下载
总结
刚接触swift不久就直接写东西，确实不好写，swift为了安全做了很多努力，但却增加了一些注意事项。一个Int乘以一个Double都报错的“强类型“检查实在不习惯。但是不得不说这门语言确实有意思，省略小括号，不用分号，switch，where…以后多接触，说不定就能喜欢上这门语言了:]
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