編程一個UIButton來更改UILabel

Question

我想在iOS單一視圖應用程序中使用Objective-C來編程一個UIButton來更改UILabel中的文本。有沒有辦法運行一個函數來實現這個在我的「ViewController.m」文件中實現？

這裏是我的源代碼：

#import "ViewController.h" 

@interface ViewController() 

@end 

@implementation ViewController 

- (void)loadView { 

//UIBUTTON 

//allocate the view 
self.view = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]]; 

//set the view's background color 
self.view.backgroundColor = [UIColor whiteColor]; 

//create the button 
UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 

//set the position of the button 
button.frame = CGRectMake(50, 280, 280, 50); 

//set the font size of the button 
button.titleLabel.font = [UIFont systemFontOfSize:40]; 

//set the text color of the button, before it is pressed 
[button setTitleColor:[UIColor blueColor] forState:UIControlStateNormal]; 

//set the text color of the button, while it is pressed 
[button setTitleColor:[UIColor grayColor] forState:UIControlStateHighlighted]; 

//set the button's title 
[button setTitle:@"3" forState:UIControlStateNormal]; 

//listen for clicks 
[button addTarget:self action:@selector(buttonPressed) 
forControlEvents:UIControlEventTouchUpInside]; 

//add the button to the view 
[self.view addSubview:button]; 

//UILABEL 
UILabel *Question=[ [UILabel alloc] initWithFrame:CGRectMake(10,200,350,60)]; 
Question.text=@"How many horns does a Triceratops have?"; 
Question.backgroundColor = [UIColor grayColor]; 
Question.textColor = [UIColor whiteColor]; 
Question.font=[UIFont fontWithName:@"Helvetica" size:18 ]; 
[self.view addSubview:Question]; 
} 

-(void)buttonPressed { } 

@end 

是否有可能引發文本的變化在我的buttonPressed函數？非常感謝任何人的幫助！

Answer 1

的問題是，當你創建你的標籤，並將其添加到界面...

UILabel *Question=[ [UILabel alloc] initWithFrame:CGRectMake(10,200,350,60)]; 
// ... 
[self.view addSubview:Question]; 

...你沒有保持對它的引用。所以現在，在buttonPressed，你沒有辦法談論標籤。

使屬性：

@interface ViewController() 
@property (nonatomic, weak) UILabel* questionLabel; 
@end 

...當你創建標籤，記得設置該屬性到該標籤。 現在您將可以通過該屬性在buttonPressed（或其他任何地方）訪問該標籤的text。