Question

我已经在一个方法中创建了NSMutable Array并将其添加到NSMutable Array中。以下是代码

-(void)setupSegmentButtons {

NSInteger numControllers = 7;

NSDate *now = [NSDate date];
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *beginningOfThisWeek;
NSTimeInterval durationOfWeek;

[calendar rangeOfUnit:NSWeekCalendarUnit
            startDate:&beginningOfThisWeek
             interval:&durationOfWeek
              forDate:now];

NSMutableArray *dtDate = [@[] mutableCopy];

NSDateComponents *comps = [calendar components:NSUIntegerMax fromDate:now];
NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd/MM/YYYY"];

for (int i = 0; i<numControllers; i++) {

    UIButton *button = [[UIButton alloc]initWithFrame:CGRectMake(X_BUFFER+i*(self.view.frame.size.width-2*X_BUFFER)/numControllers-X_OFFSET, Y_BUFFER, (self.view.frame.size.width-2*X_BUFFER)/numControllers, HEIGHT)];

    [navigationView addSubview:button];

    NSString *dateString = [dateFormatter stringFromDate:[calendar dateFromComponents:comps]];

    [dtDate addObject:dateString];

    [button addTarget:self action:@selector(tapSegmentButtonAction:) forControlEvents:UIControlEventTouchUpInside];

    ++comps.day;
}

//****** Manage to display my array with all the dates
NSLog(@" Can get my array : %@",dtDate);

}

但是当点击按钮并调用另一个方法时，NSMutable Array dtDate返回（null），为什么？

-(void)tapSegmentButtonAction:(UIButton *)button {

//Can't get the NSMutable Array here 
NSLog(@" Returns Null : %@",dtDate);

NSString *txtDate = dtDate[0];
//Returns NULL
NSLog(@"txtDate=%@",txtDate);
}

Answer 1

您的方法tapSegmentButtonAction:在没有任何声明的情况下访问dtDate ，表明它是实例或全局变量。

您的方法setupSegmentButtons 声明变量dtDate创建一个隐藏任何实例或全局同名的局部变量。

而不是：

NSMutableArray *dtDate = [@[] mutableCopy];

你应该尝试：

dtDate = [NSMutableArray new];

HTH

Answer 2

dtDate是您方法中的局部变量..

如果你有一个存储dtDate变量的属性

你应该执行

self.yourProperty = dtDate

Answer 3

//假设它被写为全局变量

NSMutableArray *dtDate;

-(void)setupSegmentButtons {

NSInteger numControllers = 7;

NSDate *now = [NSDate date];
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *beginningOfThisWeek;
NSTimeInterval durationOfWeek;

[calendar rangeOfUnit:NSWeekCalendarUnit
            startDate:&beginningOfThisWeek
             interval:&durationOfWeek
              forDate:now];

dtDate = [NSMutableArray alloc] init];

NSDateComponents *comps = [calendar components:NSUIntegerMax fromDate:now];
NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd/MM/YYYY"];

for (int i = 0; i<numControllers; i++) {

    UIButton *button = [[UIButton alloc]initWithFrame:CGRectMake(X_BUFFER+i*(self.view.frame.size.width-2*X_BUFFER)/numControllers-X_OFFSET, Y_BUFFER, (self.view.frame.size.width-2*X_BUFFER)/numControllers, HEIGHT)];

    [navigationView addSubview:button];

    NSString *dateString = [dateFormatter stringFromDate:[calendar dateFromComponents:comps]];

    [dtDate addObject:dateString];
    NSLog(@"dtDate inside loop =%@",dtDate);// for checking wheter at ths instance You have value or not
    button.tag = i;

    [button addTarget:self action:@selector(tapSegmentButtonAction:) forControlEvents:UIControlEventTouchUpInside];

    ++comps.day;
}

//****** Manage to display my array with all the dates
NSLog(@" Can get my array : %@",dtDate);

}

-(void)tapSegmentButtonAction:(UIButton *)button {

//Can't get the NSMutable Array here 
NSLog(@" Returns Null : %@",dtDate);

NSString *txtDate = dtDateArray[0];
//Returns NULL
NSLog(@"txtDate=%@",txtDate);
}

Answer 4

将NSMutable数组放在viewDidLoad后，它变为Global

- (void)viewDidLoad
{
[super viewDidLoad];

dtDate = [[NSMutableArray alloc] init];
}

不要理解为什么，如果有人能够解释，那将是伟大的。

NSMutable Array不在另一个方法中返回值

4 个答案: