How to change a UILabel using a slider - ios

Question

I'm new to objective c and I want to change a label text to the value of a slider.
Should I add some text first and should I add the UILabel inside the Action?
What I have is:
#import "slRootViewController.h"
#implementation slRootViewController {
NSMutableArray *_objects;
}
- (void)loadView {
[super loadView];
_objects = [[NSMutableArray alloc] init];
self.title = #"Slider Test ";
CGRect frame = CGRectMake(0.0, 0.0, 200.0, 10.0);
UISlider *slider = [[UISlider alloc] initWithFrame:frame];
[slider addTarget:self action:#selector(sliderAction:) forControlEvents:UIControlEventValueChanged];
[slider setBackgroundColor:[UIColor clearColor]];
slider.minimumValue = 0.0;
slider.maximumValue = 50.0;
slider.continuous = YES;
slider.value = 25.0;
UILabel *sliderText=[ [UILabel alloc] initWithFrame:CGRectMake(273,442,32,20)];
[self.view addSubview:slider];
[self.view addSubview:sliderText];
}
// voids
-(void)sliderAction:(id)sender
{
UISlider *slider = (UISlider*)sender;
self.sliderText.text=[NSString stringWithFormat:#"%f", slider.value];
//-- Do further actions
}
#end
But I'm getting an error saying
error: Use of undeclared identifier "sliderText"

Answer 1

Define the Label object Globally in your file.
#implementation slRootViewController {
NSMutableArray *_objects;
UILabel *sliderText; //Define globally label object
}
and change name or any activity for this label using globally object, like a
Change name,
sliderText.text = #"Set Name";
Set Text Color,
sliderText.textColor = [UIColor redColor];
and so on......

Answer 2

The error is due to the variable's scope. You are declaring sliderText inside loadView and finally accessing it in another method called sliderAction. It should be an instance variable (defined in either your .h or .m file depending on your needs). Just like you did with _objects.
#implementation slRootViewController {
NSMutableArray *_objects;
UILabel *sliderText; // Move it to your .h file if needed
}

Answer 3

It should be like this
#import "slRootViewController.h"
#implementation slRootViewController {
NSMutableArray *_objects;
}
#property (strong ,nonatomic) UILabel *sliderText;
- (void)loadView {
[super loadView];
_objects = [[NSMutableArray alloc] init];
self.title = #"Slider Test ";
CGRect frame = CGRectMake(60, 200.0, 200.0, 10.0);
UISlider *slider = [[UISlider alloc] initWithFrame:frame];
[slider addTarget:self action:#selector(sliderAction:) forControlEvents:UIControlEventValueChanged];
[slider setBackgroundColor:[UIColor clearColor]];
slider.minimumValue = 0.0;
slider.maximumValue = 50.0;
slider.continuous = YES;
slider.value = 25.0;
self.sliderText = [[UILabel alloc] initWithFrame:CGRectMake(60,CGRectGetMaxY(slider.frame)+40,120,20)];
//You can change y axis what you want
[self.view addSubview:slider];
[self.view addSubview:self.sliderText];
}
// voids
-(void)sliderAction:(id)sender
{
UISlider *slider = (UISlider*)sender;
self.sliderText.text=[NSString stringWithFormat:#"%f", slider.value];
//-- Do further actions
}

Answer 4

Let me clear with your error.
When you try to access any object in controller or class, which you haven't declared, or you declared in one method and you try to call its outside method (that's called as Out of Scope), then you will get an error like this.
Solutions:
1) Check your header file about the variable declaration.
2) Here you write self.sliderText. So make sure you have proper synthesize it.

Answer 5

You just need to change the UILabel declaration in implementation part..,just shown below in code
#import "slRootViewController.h"
#implementation slRootViewController {
NSMutableArray *_objects;
UILabel *sliderText; //<<---
}
- (void)loadView {
[super loadView];
_objects = [[NSMutableArray alloc] init];
self.title = #"Slider Test ";
CGRect frame = CGRectMake(0.0, 0.0, 200.0, 10.0);
UISlider *slider = [[UISlider alloc] initWithFrame:frame];
[slider addTarget:self action:#selector(sliderAction:) forControlEvents:UIControlEventValueChanged];
[slider setBackgroundColor:[UIColor clearColor]];
slider.minimumValue = 0.0;
slider.maximumValue = 50.0;
slider.continuous = YES;
slider.value = 25.0;
sliderText=[ [UILabel alloc] initWithFrame:CGRectMake(273,442,32,20)];
[self.view addSubview:slider];
[self.view addSubview:sliderText];
}
// voids
-(void)sliderAction:(id)sender
{
UISlider *slider = (UISlider*)sender;
sliderText.text=[NSString stringWithFormat:#"%f", slider.value];
}
#end