Ios 为什么可以'；t我使用“；“强”；或；分配；在这里I'；MVC模式下的m编程

我正试图做出一个选择的观点，我有一个充满国家名称的plist。现在，我想通过我的模型加载这些数据，并用我的控制器将它们显示在picker视图上。起初，我使用“assign”和“strong”来描述文件“WXFlagsModel”中的属性“name”，但一旦我开始滚动选择器，程序就崩溃了！然后我试着“复制”，然后一切都很好。有人能告诉我为什么吗？谢谢大家！ 1.这是“WXFlagsModel.h”文件的一部分

Xcode告诉我：

线程1:EXC\u错误访问（代码=1，地址=0x20）

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PS：我不允许在这里嵌入屏幕截图，所以我只是键入单词。

assign

用于基本类型

strong

用于目标c类类型。请提供崩溃的详细信息，包括异常名称、消息和堆栈跟踪。我打赌崩溃的不是返回语句。代码中有任何警告吗？

        #import <Foundation/Foundation.h>

@interface WXFlagsModel : NSObject

@property (copy ,nonatomic) NSString *name;

@property (strong,nonatomic)NSString *icon;

-(instancetype)initWithDict:(NSDictionary*)dict;

+(instancetype)flagsWithDict:(NSDictionary*)dict;

+(NSArray*)flags;

@end

#import "ViewController.h"
#import "WXFlagsModel.h"

@interface ViewController ()<UIPickerViewDataSource,UIPickerViewDelegate>
@property (nonatomic,strong) NSArray *flags;
@end

@implementation ViewController

#pragma mark - lazy loading
-(NSArray *)flags
{
    if (_flags == nil) {
        NSArray *array = [NSArray arrayWithContentsOfFile:[[NSBundle mainBundle]pathForResource:@"flags.plist" ofType:nil]];
        
        NSMutableArray *arrayM = [NSMutableArray array];
        for (NSDictionary *dict in array) {
            WXFlagsModel *model = [WXFlagsModel flagsWithDict:dict];
            
            [arrayM addObject:model];
        }
        _flags = arrayM;
    }
    return _flags;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    NSLog(@"%@",self.flags);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - picker view delegate

#pragma mark - picker view data source
// returns the number of 'columns' to display.
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    return 1;
}

// returns the # of rows in each component..
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    return self.flags.count;
}

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
//    WXFlagsModel *flag = [WXFlagsModel new];
    WXFlagsModel *flag = self.flags[row];
    return flag.name;
}


#pragma  mark - private methods

@end

return flag.name;