iOS6和iOS7的navigation空白问题

//有时候你的iOS6和iOS7的风格会有问题如上
//可以通过设置这个属性改写
self.navigationController.navigationBar.translucent = YES;

/*
下面是apple文档
New behavior on iOS 7.
Default is YES.
You may force an opaque background by setting the property to NO.
If the navigation bar has a custom background image, the default is inferred
from the alpha values of the image—YES if it has any pixel with alpha < 1.0
If you send setTranslucent:YES to a bar with an opaque custom background image
it will apply a system opacity less than 1.0 to the image.
If you send setTranslucent:NO to a bar with a translucent custom background image
it will provide an opaque background for the image using the bar's barTintColor if defined, or black
for UIBarStyleBlack or white for UIBarStyleDefault if barTintColor is nil.
*/
@property(nonatomic,assign,getter=isTranslucent) BOOL translucent NS_AVAILABLE_IOS(3_0); // Default is NO on iOS 6 and earlier. Always YES if barStyle is set to UIBarStyleBlackTranslucent