NSLog Printing (null) for object?

Question

每当按下"保存"按钮时，我都会使用委派将对象从我的 AssignmentViewController 传递到我的 TableViewController。

我

正在尝试打印出我应该刚刚保存并忽略的对象的内容，但 NSLog 显示 （null）。 有人可以帮我弄清楚为什么吗？

AssignmentViewController.h

@protocol AssignmentDelegate <NSObject>
-(void)newAssignment:(Homework *)assignment;
@end
@interface Assignment : UIViewController <UITextViewDelegate> 
@property (nonatomic,weak)id<AssignmentDelegate> delegate;
@property(nonatomic) IBOutlet UITextField *ClassNameField;
@property(nonatomic) IBOutlet UILabel *ClassNameLabel;
@property(nonatomic) IBOutlet UITextField *AssignmentTitleField;
@property(nonatomic) IBOutlet UILabel *AssignmentTitleLabel;

@property (nonatomic, strong) Homework *homeworkAssignment;

- (IBAction)Save:(UIButton *)sender;

AssignmentViewController.m

- (IBAction)Save:(UIButton *)sender {
self.homeworkAssignment = [[Homework alloc] init];
self.homeworkAssignment.className = self.ClassNameField.text;
self.homeworkAssignment.assignmentTitle = self.AssignmentTitleField.text;
self.homeworkAssignment.assignmentDiscription = self.DiscriptionTextView.text;
[self.delegate newAssignment:self.homeworkAssignment];
 NSLog(@"%@",self.delegate);   //PRINTS (null)*******************************
[self.navigationController popViewControllerAnimated:YES];
}

这是我的TableViewController.h，以防问题出在这里

@interface AssignmentTableController : UITableViewController
<
AssignmentDelegate
>
@property (strong, nonatomic) NSMutableArray *alist;

@end

TableViewController.m

-(NSMutableArray *)alist
{
if (!_alist) {
    _alist = [[NSMutableArray alloc]init];
}
return _alist;
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if([segue.identifier isEqualToString:@"to2"]) {
    Assignment *assignmentViewController = segue.destinationViewController;
    assignmentViewController.delegate = self;
}
}
-(void)newAssignment:(Homework *)assignment
{

[self.alist addObject:assignment];
NSString *filePath = [self dataFilePath];
[NSKeyedArchiver archiveRootObject:self.alist toFile:filePath];
[self.tableView reloadData];
}

Answer 1

通过验证 segue id 并在方法的 if 语句中放置一个 beakpoint 来确保 - (void) prepareForSegue 正在运行。