1.UIImageView不支持内部图片平铺(tile)

2.资源中的图片要用小写的,模拟器中可能不区分大小写,但在真机中区分.

   [UIImage imageNamed:@""]; 在设备中区分大小写

3.UIView没有背景图属性,有背景色属性.设置背景图可以用addSubView(backgroundImage);，推荐的是设置背景色。

4.[UIImage imageNamed:@""];//它是有缓存特性的

  This method looks in the system caches for an image object with the specified name and returns that object if it exists. If a matching image object is not already in the cache, this method loads the image data from the specified file, caches it, and then returns the resulting object.

  On a device running iOS 4 or later, the behavior is identical if the device’s screen has a scale of1.0. If the screen has a scale of2.0, this method first searches for an image file with the same filename with an@2xsuffix appended to it. For example, if the file’s name isbutton, it first searches forbutton@2x. If it finds a 2x, it loads that image and sets thescale property of the returnedUIImage object to2.0. Otherwise, it loads the unmodified filename and sets thescale property to1.0.

   On iOS 4 and later, the name of the file is not required to specify the filename extension. Prior to iOS 4, you must specify the filename extension.

    可能在多次操作之后，应用经常发生内存警告从而导致自动退出的问题。定位之后发现是由于[UIImage imageNamed: @""]分配的图像都没有释放引起的。而之前从官方的reference中得到的信息应该是[UIImage imageNamed:@""]分配的图像系统会放到cache里面。而关于cache管理的规则就没有明确的介绍。由此看来[UIImage imageNamed:]只适合与UI界面中小的贴图的读取，而一些比较大的资源文件应该尽量避免使用这个接口。

  5.  + (UIImage *)imageWithContentsOfFile:(NSString *)path  //这个方法does not cache the image object.