为什么我的目标C实现文件不能识别我的导入语句?

这是我的头文件

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import <PolygonShape.h>

@interface Controller : NSObject {
    IBOutlet UIButton *decreaseButton;
    IBOutlet UIButton *increaseButton;
    IBOutlet UILabel *numberOfSidesLabel;
    //IBOutlet PolygonShape *shape;
}
- (IBAction)decrease;
- (IBAction)increase;
@end

这是我的实现文件

#import "Controller.h"

@implementation Controller
- (IBAction)decrease {
    //shape.numberOfSides -= 1;
}

- (IBAction)increase {
    //shape.numberOfSides += 1;
}
@end

为什么我的 #import "Controller.h" 线路?

error: PolygonShape.h: No such file or directory

polygonshape.h和.m文件与controller类位于同一项目和同一目录中。