从AlertView例解设置view背景的几种方法

UIAlertView *alv_obj = [[[UIAlertView alloc] initWithTitle:@"AlertView"
message:@"This is Example！"
delegate:nil
cancelButtonTitle:@"cancel"
otherButtonTitles:@"confirm", nil] autorelease];
[alv_obj show];

// undocument API UIAlertView类头文件里面带 “ _”的成员是可以通过 valueforkey来引用的。但这些都是不公开的，私有方法
通过字典的方式取出其对象就可以操作其属性。如下：
UILabel *theTitle = [alv_obj valueForKey:@"_titleLabel"];
[theTitle setTextColor:[UIColor greenColor]];

UILabel *theBody = [alv_obj valueForKey:@"_bodyTextLabel"];
[theBody setTextColor:[UIColor blueColor]];

/* 第一种自定义方法*/
UIImageView *imgv = [alv_obj valueForKey:@"_backgroundImageView"];
imgv.image = [UIImage imageNamed:@"loveChina.png"];

/* 第二种自定义方法,因有过期属性的使用，所以新版iOS中无效*/
// undocument API
UIImage *theImage = [UIImage imageNamed:@"loveChina.png"];
theImage = [theImage stretchableImageWithLeftCapWidth:0.0 topCapHeight:0.0];
CGSize theSize = [alv_obj frame].size;

UIGraphicsBeginImageContext(theSize);
[theImage drawInRect:CGRectMake(0, 0, theSize.width, theSize.height)];
theImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
alv_obj.layer.contents = (id)[theImage CGImage]; // iOS4.0开始不支持contents属性

 /* 第三种自定义方法*/
   //遍历alv_obj对象的子view，获取其UIImageView视图
   for (UIView *v in [alv_obj subviews])
{
      if ([v isKindOfClass:[UIImageView class]])
{
        UIImage *theImage = [UIImage imageNamed:@"loveChina.png"];
       ((UIImageView *)v).image = theImage;
     }
   }

 /* 第四种自定义方法 */
UIView *additionBackgroundView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, alv_obj.frame.size.width-30, alv_obj.frame.size.height-20)];
additionBackgroundView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"loveChina.png"]];
#if TARGET_IPHONE_SIMULATOR
[alv_obj insertSubview:additionBackgroundView atIndex:1];
#else
[alv_obj insertSubview:additionBackgroundView atIndex:0];
#endif
[additionBackgroundView release];

UIAlertView *theAlert = [[[UIAlertView alloc] initWithTitle:@"Atention"
message:@"我是中国人！"
delegate:nil
cancelButtonTitle:@"取消"
otherButtonTitles:@"确定", nil] autorelease];
UIImage *alertImage = [UIImage imageNamed:@"loveChina.png"];
UIImageView *backgroundImageView = [[UIImageView alloc] initWithImage:alertImage];
backgroundImageView.frame = CGRectMake(0, 0, 282, 160);
backgroundImageView.contentMode = UIViewContentModeScaleToFill;
[theAlert addSubview:backgroundImageView];
[theAlert sendSubviewToBack:backgroundImageView];

[theAlert show];
[theAlert release];

本质：作为复合控件，UIAlertView是由多个基本控件组合而成，每个基本控件的功能也是UIAlertView的功能的有效组成部分。所以，我们想修改UIAlertView的某个属性，可以通过修改控制UIAlertView的该属性的基本控件而达到目的。这是一个整体和局部的分析方法。例如本例，我们想修改UIAlertView的背景图，就是通过获取到控制UIAlertView的背景图的子控件UIImageView而达到目的的。

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