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複数回addSubviewを呼んだ時の挙動について

Last updated at Posted at 2015-07-18

概要

動的にUIViewに別のUIViewを追加したい場合には、addSubviewというメソッドが利用できます。

//view1にview2を追加したい場合
        var view1 = UIView(frame:CGRectMake(0, 0, 200, 200))
        view1.backgroundColor = UIColor.blueColor()
        var view2 = UIView(frame:CGRectMake(50, 50, 100, 100))
        view2.backgroundColor = UIColor.greenColor()
        view1.addSubview(view2)

Figure:1

では、view2をview1以外のビューに対してaddSubviewを使って追加したらどうなるのでしょうか??

        //view1, view1Aにview2を追加したい場合
        var view1 = UIView(frame:CGRectMake(0, 0, 200, 200))
        view1.backgroundColor = UIColor.blueColor()
        var view1A = UIView(frame:CGRectMake(0, 300, 200, 200))
        view1A.backgroundColor = UIColor.redColor()
        var view2 = UIView(frame:CGRectMake(50, 50, 100, 100))
        view2.backgroundColor = UIColor.greenColor()
        view1.addSubview(view2)
        view1A.addSubview(view2)

スクリーンショット 2015-07-18 13.14.26.png

最後に追加したview1Aにのみ追加されるようです。
ということは、view1に追加されていたview2はremoveFromSuperviewによって削除されたのでしょうか？
view1にもview1Aにも追加されると思ってしまうケースも多いような気がします :sweat:

検証

Case1: 追加先を順々に変更してみる

見た目で挙動を確認するために次のようなコードを書いてみました。

        let averageHeight = CGRectGetHeight(UIScreen.mainScreen().bounds) / 11.0
        let averageWidth = CGRectGetWidth(UIScreen.mainScreen().bounds) / 2.0
        //5つviewを追加するためのviewを用意する
        var subview1 = UIView(frame: CGRectMake(averageHeight,
                                                averageHeight,
                                                averageHeight,
                                                averageHeight))
        subview1.backgroundColor = UIColor.blueColor()
        subview1.center = CGPointMake(averageWidth, subview1.center.y)
        var subview2 = UIView(frame: CGRectMake(averageHeight,
                                                averageHeight*3,
                                                averageHeight,
                                                averageHeight))
        subview2.backgroundColor = UIColor.greenColor()
        subview2.center = CGPointMake(averageWidth, subview2.center.y)
        var subview3 = UIView(frame: CGRectMake(averageHeight,
                                                averageHeight*5,
                                                averageHeight,
                                                averageHeight))
        subview3.backgroundColor = UIColor.redColor()
        subview3.center = CGPointMake(averageWidth, subview3.center.y)
        var subview4 = UIView(frame: CGRectMake(averageHeight,
                                                averageHeight*7,
                                                averageHeight,
                                                averageHeight))
        subview4.backgroundColor = UIColor.yellowColor()
        subview4.center = CGPointMake(averageWidth, subview4.center.y)
        var subview5 = UIView(frame: CGRectMake(averageHeight,
                                                averageHeight*9,
                                                averageHeight,
                                                averageHeight))
        subview5.backgroundColor = UIColor.blackColor()
        subview5.center = CGPointMake(averageWidth, subview5.center.y)

        //追加するビューを用意する
        targetView = UIView(frame: CGRectMake(averageHeight/4, averageHeight/4, averageHeight/2, averageHeight/2))
        targetView.layer.cornerRadius = 4.0
        targetView.backgroundColor = UIColor.purpleColor()
        NSTimer.scheduledTimerWithTimeInterval(2.0, target: self, selector: "moveTargetView:", userInfo: nil, repeats: true)
        viewList = [subview1, subview2, subview3, subview4, subview5]
        subview1.addSubview(targetView)

    func moveTargetView(timer:NSTimer) {
        //追加先ビューの変更
        currentIndex = (currentIndex >= viewList.count - 1) ? 0 : currentIndex + 1
        let view = viewList[currentIndex]
        view.addSubview(targetView)
    }

gif.gif

moveTargetView:がcallされる度にビューの位置が変わっていますね。
追加される先は１つのように見えます。

Case2: RetainCountの確認

以下の様なコードを書いて追加されたchildViewのRetainCountを計測してみました。

    UIView *parentView = [[UIView alloc] init];
    UIView *childView = [[UIView alloc] init];
    NSLog(@"Number of RetainCount = %ld", (long)CFGetRetainCount((__bridge CFTypeRef)childView));
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    NSLog(@"Number of RetainCount = %ld", (long)CFGetRetainCount((__bridge CFTypeRef)childView));


2015-07-18 13:00:03.168 test-objC[9989:328391] Number of RetainCount = 1
2015-07-18 13:00:03.170 test-objC[9989:328391] Number of RetainCount = 2

childViewのRetainCountはインスタンス生成 & parentViewへのaddSubviewの2回分しかないみたいです。

念のため、ParentViewのsubviewsの数も確認してみました。

    UIView *parentView = [[UIView alloc] init];
    UIView *childView = [[UIView alloc] init];
    NSLog(@"Number of Subviews = %lu", (unsigned long)parentView.subviews.count);
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    [parentView addSubview:childView];
    NSLog(@"Number of Subviews = %lu", (unsigned long)parentView.subviews.count);


2015-07-18 13:03:16.407 test-objC[10052:330128] Number of Subviews = 0
2015-07-18 13:03:16.408 test-objC[10052:330128] Number of Subviews = 1

Case3: addSubviewをする先を変更した場合に[will|did]MoveToSuperviewを確認

例えば、view1にview2を追加した場合やview2をview1から削除した場合、view2に対して,
willMoveToSuperview(newSuperview: UIView?)、didmoveToSuperView()が呼ばれます。
willMoveToSuperviewの第一引数がnilの場合は、superviewから削除された場合です。 確認するため、以下のようにView2`クラスのそれぞれのメソッドでログを吐くようにしてみました :bow:

        var view1 = UIView(frame:CGRectMake(0, 0, 200, 200))
        view1.backgroundColor = UIColor.blueColor()
        var view1A = UIView(frame:CGRectMake(0, 300, 200, 200))
        view1A.backgroundColor = UIColor.redColor()
        var view2 = View2(frame:CGRectMake(50, 50, 100, 100))
        view2.backgroundColor = UIColor.greenColor()
        view1.addSubview(view2)   //View2クラスのview2にview1を追加
        view1A.addSubview(view2)  //View2クラスのview2にview1Aを追加
    
class View2: UIView {
    override func willMoveToSuperview(newSuperview: UIView?) {
        let isExistSuperview = (newSuperview != nil) ? true : false
        println("willMoveToSuperview: \(isExistSuperview)")
    }
    override func didMoveToSuperview() {
        println("didMoveToSuperview")
    }
}


willMoveToSuperview: true
didMoveToSuperview
willMoveToSuperview: true
didMoveToSuperview

あれ。。。?! 呼ばれてないというかここは通らないよう...。
明示的にview1からview1Aに追加先を変更する前に、removeFromSuperviewを呼ぶと、やはりそれぞれ３回ずつ呼ばれました。

willMoveToSuperview: true
didMoveToSuperview
willMoveToSuperview: false
didMoveToSuperview
willMoveToSuperview: true
didMoveToSuperview

まとめ

  • 同じUIViewクラスのオブジェクトを別のUIViewクラスのオブジェクトに追加した場合、直前の追加先からは削除され、参照カウンタに変動はない
  • 暗黙的にremoveFromSuperviewが呼ばれているような挙動だが、willMoveToSuperviewなどは呼ばれない

ということでした :smiley:

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