iOS 多 UIView 添加點擊手勢：為何共用 UITapGestureRecognizer 失效？

問題現象

同一 UITapGestureRecognizer 實例分別添加給 sendView、payView、receiverView、commentView，結果**只有最後添加的 commentView 能響應點擊**。

根本原因

UIGestureRecognizer **一次只能附屬於一個 View**。當對同一手勢實例呼叫 addGestureRecognizer: 時，系統會**自動從先前的 View 移除**，再添加到新 View。因此前三個 View 實際上並未持有該手勢。

正確做法：每個 View 獨立實例

// 方式一：分別建立實例（推薦，語意清晰）
UITapGestureRecognizer *tap1 = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewClick:)];
[self.sendView addGestureRecognizer:tap1];

UITapGestureRecognizer *tap2 = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewClick:)];
[self.payView addGestureRecognizer:tap2];

UITapGestureRecognizer *tap3 = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewClick:)];
[self.receiverView addGestureRecognizer:tap3];

UITapGestureRecognizer *tap4 = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewClick:)];
[self.commentView addGestureRecognizer:tap4];

進階：統一處理點擊邏輯

- (void)viewClick:(UITapGestureRecognizer *)sender {
    UIView *tappedView = sender.view;
    if (tappedView == self.sendView) { /* 發送邏輯 */ }
    else if (tappedView == self.payView) { /* 支付邏輯 */ }
    else if (tappedView == self.receiverView) { /* 收件邏輯 */ }
    else if (tappedView == self.commentView) { /* 評論邏輯 */ }
}

替代方案：單一手勢 + hitTest（不推薦）

在共同父視圖添加手勢，通過 hitTest:withEvent: 判斷點擊落在哪個子視圖。**缺點**：事件傳遞鏈複雜、易與子視圖自身手勢衝突、難以維護。

Swift 版本

let views = [sendView, payView, receiverView, commentView]
views.forEach { view in
    let tap = UITapGestureRecognizer(target: self, action: #selector(viewClick(_:)))
    view.addGestureRecognizer(tap)
}

@objc func viewClick(_ sender: UITapGestureRecognizer) {
    switch sender.view {
    case sendView: /* ... */ break
    case payView: /* ... */ break
    case receiverView: /* ... */ break
    case commentView: /* ... */ break
    default: break
    }
}

總結

一個手勢識別器只能綁定一個視圖。多視圖需多實例。這是 UIKit 設計決策，非 Bug。記住：addGestureRecognizer: 會自動從舊視圖移除。