相关疑难解决方法(0)

我刚刚掌握了Objective-C 2.0

当我尝试在Xcode中构建以下内容时,它失败了.编译器的错误如下:

unsafe_unretained属性'title'的现有ivar'title'必须是__unsafe_unretained.

// main.m
#import <Foundation/Foundation.h>
#import "Movie.h"
int main (int argc, const char * argv[]){
    Movie *movie = Movie.new;

    NSLog(@"%@", movie);

    return 0;
}

// movie.h
#import <Foundation/Foundation.h>

@interface Movie : NSObject{
    NSString *title;
    int year;
    int rating;
}

@property(assign) NSString *title;
@property(assign) int rating;
@property(assign) int year;

@end

#import "Movie.h"

@implementation Movie;

@synthesize title; // this seems to be issue - but I don't understand why?
@synthesize rating;
@synthesize year;

@end

谁能解释我哪里出错了？