UILabel 为 nil - 无法更新 UILabel 的文本

Question

所以这是一个初学者的问题，我不得不向你们承认，但我真的不知道我应该做什么，我花了几个小时来尝试解决它。

所以：我的问题是为什么当我想更新它的文本时 UILabel 为 nil？

详情：

1:我有两个视图，DetectionView 是初始视图，在该视图按钮的工具栏中有一个 UILabel 和一个名为 "Setting" 的条形按钮项，第二个视图是 EnterCommandView，其中此视图顶部的工具栏中有一个 UITextField 和一个名为 "save" 的条形按钮项。

2：输入字符串后，应用程序启动完成后，单击“设置”，然后从第一个视图转到第二个视图。其次，我在 UITextField 中输入一些字符串，然后单击 "Save" 按钮，第二个视图被关闭，然后我返回初始视图，

3: 当我回到InitialView的时候，刚刚输入的String应该出现在UILabel中，但是，对不对，这正是我的问题，然后我设置了一个断点我更新 UILabel 的地方，我在这个 post 的末尾有信息，说 UILabel 是 nil

代码：

EnterCommnadViewController.h

#import <UIKit/UIKit.h>
#import "RscMgr.h"

@protocol EnterCommandDelegate <NSObject>
@optional
-(void) commandEntered:(NSString*)command;
@end
@interface EnterCommandViewController : UIViewController  <RscMgrDelegate,EnterCommandDelegate>
{
RscMgr* rscMgr;
IBOutlet UITextField *inputTextField;
}
-(void)sendMessage:(NSString*)message;
-(id)initWithDelegate:(id)delegateToBe;
- (IBAction)cancelPressed;
- (IBAction)savePressed;
@property (nonatomic,weak) id<EnterCommandDelegate> delegate; 
@end

EnterCommandViewController.m

#import "EnterCommandViewController.h"
#import "DetectionViewController.h"
@interface EnterCommandViewController () <UITextFieldDelegate>
{
@private
BOOL connected;
}
@end
@implementation EnterCommandViewController
@synthesize delegate;

- (void)viewDidLoad {
[super viewDidLoad];
[inputTextField becomeFirstResponder];
}

-(void) viewWillAppear:(BOOL)animated{
[super viewWillAppear:animated];
inputTextField.delegate = self;
}

-(void) viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
inputTextField.delegate = nil;
}

- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
- (IBAction)cancelPressed {
[self dismissViewControllerAnimated:YES completion:^{}];
}

- (IBAction)savePressed {
if([[[UIDevice currentDevice]systemVersion] compare:@"7.0"  options:NSNumericSearch] != NSOrderedAscending){
    NSLog(@"SYStem version > 7.0");
}
if(delegate&&[delegate respondsToSelector:@selector(commandEntered:)]){
    [delegate commandEntered:inputTextField.text];
}
[self dismissViewControllerAnimated:YES completion:nil]; //commened: ^{}
}
@end

DetectionViewController.h

#import <UIKit/UIKit.h>
#import "EnterCommandViewController.h"
@interface DetectionViewController : UIViewController <EnterCommandDelegate>{
}
- (IBAction)showSettings:(UIBarButtonItem *)sender;
@property (nonatomic, strong) EnterCommandViewController* enterCVC;
@property (nonatomic, strong) IBOutlet UILabel *showReceivedCommand;
@end

DetectionViewController.m

#import <Foundation/Foundation.h>
#import "DetectionViewController.h"

@implementation DetectionViewController
@synthesize showReceivedCommand;
@synthesize enterCVC;

- (IBAction)showSettings:(UIBarButtonItem *)sender {
}

-(void) viewDidLoad{
    [super viewDidLoad];
}

#pragma mark - EnterCommandDelegate function(s)

-(void)commandEntered:(NSString *)command{
 dispatch_async(dispatch_get_main_queue(), ^{
    showReceivedCommand.text = command;
   });
}
#pragma mark -sugue
-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
 enterCVC = (EnterCommandViewController*)segue.destinationViewController;
[enterCVC setDelegate:self];
}

@end

下面是我在 DetectionViewController.m 设置断点时得到的结果 --> -(void)commmandEntered:(NSString*)command {} --> showReceivedCommand.text = 命令；

self    DetectionViewController *   0x1465132a0 0x00000001465132a0
command NSString *  @"testStringJustEntered"    0x000000017424ada0
showReceivedCommand UILabel *   0x1465149d0 0x00000001465149d0
UIView  UIView      
UIResponder UIResponder     
_layer  CALayer *   0x17409ae50 0x000000017409ae50
_gestureInfo    id  0x0 0x0000000000000000
_gestureRecognizers NSMutableArray *    nil 0x0000000000000000
_subviewCache   NSArray *   @"0 objects"    0x00000001740033b0
_charge float   0   0
_tag    NSInteger   0   0
_viewDelegate   UIViewController *  nil 0x0000000000000000
_backgroundColorSystemColorName NSString *  nil 0x0000000000000000
_countOfMotionEffectsInSubtree  NSUInteger  0   0
_viewFlags  <anonymous struct>

Answer 1

UILabel 没有任何问题，我猜问题是 "commnad" 的格式与 UILabel 中的文本不兼容。

Try follow code for the delegate function:


-(void)commandEntered:(NSString *)command{
dispatch_async(dispatch_get_main_queue(), ^{
    NSString* str1=@"";
    NSString* str=[str1 stringByAppendingString:command];
    showReceivedCommand.text = str;
});
}

UILabel 为 nil - 无法更新 UILabel 的文本

UILabel is nil- canot update text of UILabel

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