iOS 4.2中未正确绘制子类uiAlertView

我将uiAlertView子类化如下:

@interface NarrationAlertView : UIAlertView {
    UIImage * backgroundImage; //The image I want as custom background
    UILabel * textualNarrationView; //The test I wanna be displayed on the view        
}

并通过以下方式实现:

- (id)initNarrationViewWithImage:(UIImage *)image{

    if (self = [super init]){
        UILabel * alertTextLabel = [[UILabel alloc] initWithFrame:CGRectZero];
        self.textualNarrationView = alertTextLabel;
        [alertTextLabel release];
        [self addSubview:alertTextLabel];
    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    /* Here I draw the image as background */
    CGSize imageSize = self.backgroundImage.size;
    [self.backgroundImage drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
}

- (void)layoutSubviews {
    /* To fit the text */
    [textualNarrationView sizeToFit];

    CGRect textRect = textualNarrationView.frame;
    textRect.origin.x = (CGRectGetWidth(self.bounds) - CGRectGetWidth(textRect)) / 2;
    textRect.origin.y = (CGRectGetHeight(self.bounds) - CGRectGetHeight(textRect)) / 2;
    textRect.origin.y -= 70;
    textualNarrationView.frame = textRect;
}

- (void)show{
    /* Showing the view */
    [super show];
    CGSize imageSize = self.backgroundImage.size;
    self.bounds = CGRectMake(0, 0, imageSize.width, imageSize.height);
}

在以前版本的iOS上(我总是在模拟器上测试),子类运行良好,当显示时,它显示了正确绘制的自定义背景图像,并且 只是文本 在它上面,而在4.2版本中,它绘制uiAlertView经典背景(蓝色圆角矩形) 顶上 我的形象。

我做错什么了?如有任何有关uialertview编程和uiview的建议,我们将不胜感激。

更新 有人要共享uialertview替换类吗?