iOS 编程 : Problem extending UIButton class

Question

我正在尝试扩展 UIButton 类以添加一些方法，但当我尝试初始化对象时遇到一些问题。

-(id)init{

UIImage* image = [UIImage imageNamed:@"button_background.png"];    
CGRect frame=  CGRectMake(100.0, 70.0, 45.0 ,45.0);

self.frame = frame;

[self setTitle:@"title" forState:UIControlStateNormal];
[self setBackgroundImage:image forState:UIControlStateNormal];
[self setImage:image forState:UIControlStateNormal];

NSLog(@"type: %d",self.buttonType);
NSLog(@"x: %f\ny: %f\nwidth: %f\nheight: %f",frame.origin.x, frame.origin.y ,frame.size.width, frame.size.height);
NSLog(@"x: %f\ny: %f\nwidth: %f\nheight: %f",self.frame.origin.x, self.frame.origin.y ,self.frame.size.width, self.frame.size.height);

if(self != nil){
    //
}
return self;

}

它工作正常，执行过程中没有警告或错误。但是在控制台中，frame 和 self.frame 的值之间出现了一些不一致，当然按钮也没有出现在屏幕上。

type: 0
x: 100.000000
y: 70.000000
width: 45.000000
height: 45.000000

x: 0.000000
y: 0.000000
width: 0.000000
height: -1.998576

请帮帮我，我快疯了! :\

Answer 1

当您在 Objective-C 中进行子类化时，您必须 (1) 覆盖指定的初始值设定项 (2) 调用父类(super class)的指定初始值设定项。你两者都不做。

你应该做这样的事情:

/** 
 * \brief Convenience class method to replace button method of UIButton
 */
+(id)myButton
{
    MyButton* myButton = [[MyButton alloc] 
                              initWithFrame:CGMakeRect(100.0, 70.0, 45.0, 45.0)];
    return [myButton autorelaase];
}

-(id)initWithFrame:(CGRect)f
{
    if(self = [super initWithFrame:f])
    {
        UIImage* image = [UIImage imageNamed:@"button_background.png"];    

        [self setTitle:@"title" forState:UIControlStateNormal];
        [self setBackgroundImage:image forState:UIControlStateNormal];
        [self setImage:image forState:UIControlStateNormal];

        NSLog(@"type: %d",self.buttonType);
        NSLog(@"x: %f\ny: %f\nwidth: %f\nheight: %f", NSStringFromCGRect(frame));
        NSLog(@"x: %f\ny: %f\nwidth: %f\nheight: %f", NSStringFromCGRect(self.frame));
    }
    return self;
}

希望这有帮助。如果您需要更多信息，请告诉我。