HomeViewController.h
#import "DataParser.h"
@interface HomeViewController : UIViewController <DataParserDelegate>
{
UILabel *theLabel;
}
主视图控制器.m
#import "HomeViewController.h"
@implementation HomeViewController
-(void)viewDidLoad
{
theLabel = [[UILabel alloc] initWithFrame:CGRectMake(200, 200, 100, 30)];
theLabel.text = @"Bob";
theLabel.font = [UIFont italicSystemFontOfSize:20.0];
theLabel.textColor = [UIColor whiteColor];
theLabel.backgroundColor = [UIColor blueColor];
[self.view addSubview:theLabel];
UIButton *theButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[theButton addTarget:self action:@selector(clicked:) forControlEvents:UIControlEventTouchUpInside];
[theButton setTitle:@"Big Button" forState:UIControlStateNormal];
theButton.frame = CGRectMake(100,100,200,50);
[self.view addSubview:theButton];
}
-(void)clicked:(id)sender
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND,0),
^{
DataParser *data = [[DataParser alloc] init];
data.delegate = self;
[data loadSomething];
dispatch_async(dispatch_get_main_queue(),
^{
NSLog(@"Thread done");
});
});
}
-(void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
{
theLabel.frame = CGRectMake(250,250,100,30);
theLabel.text = @"This message displays fine";
}
-(void)loadMessage:(NSString *)message
{
NSLog(@"Received message: %@", message);
theLabel.frame = CGRectMake(300,300,100,30);
theLabel.text = @"This message won't display";
}
@end
数据解析器.h
@protocol DataParserDelegate;
@interface DataParser : NSObject
@property (weak, nonatomic) id <DataParserDelegate> delegate;
-(void)loadSomething;
@end
@protocol DataParserDelegate <NSObject>
-(void)loadMessage:(NSString *)message;
@end
数据解析器.m
#import "DataParser.h"
@implementation DataParser
@synthesize delegate=_delegate;
-(void)loadSomething
{
[[self delegate] loadMessage:@"ASDF"];
}
@end
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基本上,我创建一个标签并将其添加到屏幕上。此时,您可以清楚地看到一个蓝色按钮,上面有白色文字“Bob”。当您旋转屏幕时,按钮会很好地更改文本和位置。但是,如果我单击该按钮,它会创建一个 dataParser 对象,将委托设置为 self,并调用“loadSomething”。在 dataParser 对象中,“loadSomething”仅调用委托方法“loadMessage”。
问题是,当调用“loadMessage”时,NSLog 语句会正确打印(“Received message: ASDF”),但是,theLabel 不会移动,也不会更改其文本。为什么是这样?我该如何解决这个问题?