解析iOS应用的UI开发中懒加载和xib的简单使用方法

  
    self.leftbtn.enabled=(self.i!=0);
    self.rightbtn.enabled=(self.i!=4);
}

//延迟加载
/**1.图片的序号标签*/
-(UILabel *)firstlab
{
    //判断是否已经有了，若没有，则进行实例化
    if (!_firstlab) {
        _firstlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 10, 300, 30)];
        [_firstlab setTextAlignment:NSTextAlignmentCenter];
        [self.view addSubview:_firstlab];
    }
    return _firstlab;
}

/**2.图片控件的延迟加载*/
-(UIImageView *)icon
{
     //判断是否已经有了，若没有，则进行实例化
    if (!_icon) {
        _icon=[[UIImageView alloc]initWithFrame:CGRectMake(POTOIMGX, POTOIMGY, POTOIMGW, POTOIMGH)];
        UIImage *image=[UIImage imageNamed:@"biaoqingdi"];
        _icon.image=image;
        [self.view addSubview:_icon];
    }
    return _icon;
}

/**3.描述控件的延迟加载*/
-(UILabel *)lastlab
{
     //判断是否已经有了，若没有，则进行实例化
    if (!_lastlab) {
        _lastlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 400, 300, 30)];
        [_lastlab setTextAlignment:NSTextAlignmentCenter];
        [self.view addSubview:_lastlab];
    }
    return _lastlab;
}

/**4.左键按钮的延迟加载*/
-(UIButton *)leftbtn
{
     //判断是否已经有了，若没有，则进行实例化
    if (!_leftbtn) {
        _leftbtn=[UIButton buttonWithType:UIButtonTypeCustom];
        _leftbtn.frame=CGRectMake(0, self.view.center.y, 40, 40);
        [_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_normal"] forState:UIControlStateNormal];
        [_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_highlighted"] forState:UIControlStateHighlighted];
        [self.view addSubview:_leftbtn];