QQ的输入界面实现了摇一摇能清空输入框功能，感觉很实用，然后就琢磨了一下实现思路。以下是自己的实现方法：

• 首先开启“摇一摇”的监听
  [UIApplication sharedApplication].applicationSupportsShakeToEdit = YES;
• 分别重写

- (void)motionBegan:(UIEventSubtype)motion withEvent:(nullable UIEvent *)event NS_AVAILABLE_IOS(3_0);//摇一摇开始
- (void)motionEnded:(UIEventSubtype)motion withEvent:(nullable UIEvent *)event NS_AVAILABLE_IOS(3_0);//摇一摇结束
- (void)motionCancelled:(UIEventSubtype)motion withEvent:(nullable UIEvent *)event NS_AVAILABLE_IOS(3_0);//摇一摇退出

• 接着监听输入框文本的变化，当文本不为空的时候，摇一摇就弹出一个alert；为空的时候就不处理。

 - (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event {
    if (event.subtype == UIEventSubtypeMotionShake) { // 判断是否是摇动结束
        if (_b) {
            UIAlertController *alertVC = [UIAlertController alertControllerWithTitle:@"是否撤销？" message:nil preferredStyle:UIAlertControllerStyleAlert];
            UIAlertAction *action1 = [UIAlertAction actionWithTitle:@"是" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
                self.textField.text = @"";
            }];
            UIAlertAction *action2 = [UIAlertAction actionWithTitle:@"否" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
                [alertVC dismissViewControllerAnimated:YES completion:nil];
            }];
            [alertVC addAction:action1];
            [alertVC addAction:action2];
            [self presentViewController:alertVC animated:YES completion:nil];
        }
    }
}

完整的项目代码

#import "ViewController.h"

@interface ViewController (){
    BOOL _b;
}
@property (weak, nonatomic) IBOutlet UITextField *textField;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    _b = NO;
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(change) name:UITextFieldTextDidChangeNotification object:self.textField];
    //开启支持摇动
    [UIApplication sharedApplication].applicationSupportsShakeToEdit = YES;
}
//当输入框值发生变化的时候
- (void)change{
    _b = self.textField.text.length > 0;
}
//摇动结束
- (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event {
    if (event.subtype == UIEventSubtypeMotionShake) {
        if (_b) {
            UIAlertController *alertVC = [UIAlertController alertControllerWithTitle:@"是否撤销？" message:nil preferredStyle:UIAlertControllerStyleAlert];
            UIAlertAction *action1 = [UIAlertAction actionWithTitle:@"是" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
                self.textField.text = @"";
            }];
            UIAlertAction *action2 = [UIAlertAction actionWithTitle:@"否" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
                [alertVC dismissViewControllerAnimated:YES completion:nil];
            }];
            [alertVC addAction:action1];
            [alertVC addAction:action2];
            [self presentViewController:alertVC animated:YES completion:nil];
        }
    }
}
@end