UIScrollView中的实例

Question

I'm wondering about instances in UIScrollView.

I checked what is happening for the instances in UIScrollView just by writing a easy code.

Here is the code.


UIViewController.m

#import "ViewController.h"
#import "CustomScrollView.h"


@interface ViewController ()

@end

CustomScrollView *sv1, *sv2;

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    int height = self.view.frame.size.height;

    sv1 = (CustomScrollView*)[[CustomScrollView alloc] initWithFrame:CGRectMake(0, 0, 320, height/2)];
    sv1.backgroundColor = [UIColor redColor];
    [self.view addSubview:sv1];
    [sv1 setIntegerWithNum:1];

    sv2 = (CustomScrollView*)[[CustomScrollView alloc] initWithFrame:CGRectMake(0, height/2, 320, height/2)];
    sv2.backgroundColor = [UIColor blueColor];
    [self.view addSubview:sv2];
    [sv2 setIntegerWithNum:2];

    int returnVal1 = [sv1 getInteger];
    int returnVal2 = [sv2 getInteger];

    NSLog(@"Sv1:%d, Sv2:%d", returnVal1, returnVal2);
}

CustomScrollView.m

#import "CustomScrollView.h"

int number;
@implementation CustomScrollView

-(void)setIntegerWithNum:(int)num {
    number = num;
}
-(int)getInteger {
    return number;
}

By this, I see the values in the output area. I thought it will be "Sv1:1, Sv2:2" because the numbers are set as 1 and 2, respectively. But I got an output like "Sv1:2, Sv2:2"

What happened here?

Answer 1

You have only one variable of type int in your CustomScrollView.h that your setting with your setter setIntegerWithNum and then you are returning the value of " int number" with your getter getInteger . essentially with your setter, you are setting your "number" variable twice. The second time you set it with 2. so the variable number then holds 2, overwriting the previous value 1.

Therefore when you use the getter for the NSLog , you are returning the same value twice.

I would follow @Akhilrajtr's advice. simply set number as a property of type int . Then you will correctly return each object's property. That is, each individual objects int property for sv1 and sv2.

You can do this with @property (nonatomic, assign) NSInteger *number;

Answer 2

Try this,

set number as @property in CustomScrollView.h by

@property(nonatomic, assign) int number;

then in ViewController

sv1 = (CustomScrollView*)[[CustomScrollView alloc] initWithFrame:CGRectMake(0, 0, 320, height/2)];
sv1.backgroundColor = [UIColor redColor];
[self.view addSubview:sv1];
[sv1 setNumber:1];

sv2 = (CustomScrollView*)[[CustomScrollView alloc] initWithFrame:CGRectMake(0, height/2, 320, height/2)];
sv2.backgroundColor = [UIColor blueColor];
[self.view addSubview:sv2];
[sv2 setNumber:2];

int returnVal1 = [sv1 number];
int returnVal2 = [sv2 number];

NSLog(@"Sv1:%d, Sv2:%d", returnVal1, returnVal2);

Answer 3

This is because you declared

int number;

not as an instance variable or property. You can do this in two ways

1.

@interface CustomScrollView(){
int number;
}
@end

2.

@interface CustomScrollView()
@property(nonatomic)int number;

@end