UITextField禁止拖动粘贴 --UITextDragga

起始于一个需求，禁止文本输入框复制粘贴。自定义一个TextField，重写canPerFormAction方法：

- (BOOL)canPerformAction:(SEL)action withSender:(id)sender {
//    if (action == @selector(paste:)) {
//        return NO;
//    }
//    return [super canPerformAction:action withSender:sender];
    return NO;
}

直接全部禁用，完美收工。
直到某一天，测试过来一顿sao操作让我措不及防：
双击或者长按文字，进入了选中状态，再长按一会，文字就能拖动到其他文本框，实现了粘贴效果，嗯？
抢过测试机连上电脑，反复调试，canPerformAction无法拦截此sao操作，万能的千度也没找到灵感，无奈老老实实去看UITextField.h，找到了这个：

#if TARGET_OS_IOS

@interface UITextField () <UITextDraggable, UITextDroppable, UITextPasteConfigurationSupporting>
@end

#endif

直觉上UITextDraggable应该是目标。
点进去：

/* Defines a text draggable control.
 */
API_AVAILABLE(ios(11.0)) API_UNAVAILABLE(watchos, tvos)
@protocol UITextDraggable <UITextInput>

@property (nonatomic, weak, nullable) id<UITextDragDelegate> textDragDelegate;

定义文本拖动控制，就是这个了，看看UITextDragDelegate代理方法：

API_AVAILABLE(ios(11.0)) API_UNAVAILABLE(watchos, tvos)
@protocol UITextDragDelegate <NSObject>

@optional

/* Implement this to provide custom drag items when dragging out of a text control.
 * If you return an empty array here, no drag will occur.
 * The drag request provides the text range from which the user is dragging, and
 * a set of default drag items which would be used if this delegate method were
 * not implemented. You can modify and/or augment these at will.
 *
 * Note: this method might be called more than once. For instance, if the control
 * is asked to provide more items to add to an existing session.
 * You can detect this by checking the `existingItems` in the drag request.
 */
- (NSArray<UIDragItem *> *)textDraggableView:(UIView<UITextDraggable> *)textDraggableView itemsForDrag:(id<UITextDragRequest>)dragRequest;

很幸运，第一个就是寻找的方法，返回空数组就可以拦截拖动，那么解决方法有了，设置代理textDragDelegate，实现上面的代理方法，返回空数组：

- (NSArray<UIDragItem *> *)textDraggableView:(UIView<UITextDraggable> *)textDraggableView itemsForDrag:(id<UITextDragRequest>)dragRequest  API_AVAILABLE(ios(11.0)){
    return @[];
}