UISearchbar去除背景色的方法，适合iOS5/6/7/8.0beta

通常使用UISearchbar都须要去除其背景色来与自己的界面风格保持协调，可是UISearchbar的设计随着iOS版本号的升级不断地在发生着变化。以下我们通过分析UISearchbar在各个iOS版本号下的视图层次结构来探讨去除其背景色的方法。

首先使用UIView的私有方法recursiveDescription来看一下UISearchbar在iOS各个模拟器版本号中的视图层次结构。

这里使用调试命令po [self.searchBar recursiveDescription]来查看，结果例如以下：

ios5.0:

<UISearchBar: 0x76c96c0; frame = (27 1; 290 44); text = ''; autoresize = W+BM; layer = <CALayer: 0x76c9870>>

   | <UISearchBarBackground: 0x76b3d40; frame = (0 0; 290 44); userInteractionEnabled = NO; layer = <CALayer: 0x76ad4a0>>

   | <UISearchBarTextField: 0x76c9e40; frame = (5 6; 280 31); text = ''; clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x76c9fa0>>

   |    | <UITextFieldBorderView: 0x76e9e70; frame = (0 0; 280 31); opaque = NO; layer = <CALayer: 0x76e9f00>>

   |    | <UIImageView: 0x76cce70; frame = (10 8; 15 15); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x76cceb0>>

   |    | <UITextFieldLabel: 0x76cf630; frame = (32 7; 216 18); text = '提示语'; clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x76cb2c0>>

ios5.1:

<UISearchBar: 0x8378110; frame = (27 1; 290 44); text = ''; autoresize = W+BM; layer = <CALayer: 0x83782e0>>

   | <UISearchBarBackground: 0x8378630; frame = (0 0; 290 44); userInteractionEnabled = NO; layer = <CALayer: 0x83786c0>>

   | <UISearchBarTextField: 0x8378e50; frame = (0 0; 0 0); text = ''; clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x8378f90>>

ios6.0:

<UISearchBar: 0xa13fc60; frame = (27 1; 290 44); text = ''; autoresize = W+BM; layer = <CALayer: 0xa13fe40>>

   | <UISearchBarBackground: 0xa140380; frame = (0 0; 290 44); userInteractionEnabled = NO; layer = <CALayer: 0xa140440>>

   | <UISearchBarTextField: 0xa140b90; frame = (0 0; 0 0); text = ''; clipsToBounds = YES; opaque = NO; gestureRecognizers = <NSArray: 0xa1428b0>; layer = <CALayer: 0xa140cf0>>

ios6.1:

<UISearchBar: 0x8953b20; frame = (27 1; 290 44); text = ''; autoresize = W+BM; layer = <CALayer: 0x8953d10>>

   | <UISearchBarBackground: 0x8954230; frame = (0 0; 290 44); userInteractionEnabled = NO; layer = <CALayer: 0x89542f0>>

   | <UISearchBarTextField: 0x8954a30; frame = (0 0; 0 0); text = ''; clipsToBounds = YES; opaque = NO; gestureRecognizers = <NSArray: 0x8956630>; layer = <CALayer: 0x8954b90>>

ios7.0:

<UISearchBar: 0xac923d0; frame = (27 21; 290 44); text = ''; opaque = NO; autoresize = W+BM; gestureRecognizers = <NSArray: 0xac92fe0>; layer = <CALayer: 0xac92630>>

   | <UIView: 0xac92860; frame = (0 0; 290 44); clipsToBounds = YES; autoresize = W+H; layer = <CALayer: 0xac928c0>>

   |    | <UISearchBarBackground: 0xac93320; frame = (0 0; 290 44); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0xac93440>>

   |    | <UISearchBarTextField: 0xac93940; frame = (0 0; 0 0); text = ''; clipsToBounds = YES; opaque = NO; gestureRecognizers = <NSArray: 0xac953a0>; layer = <CALayer: 0xac93b20>>

   |    |    | <_UISearchBarSearchFieldBackgroundView: 0xac98520; frame = (0 0; 0 0); opaque = NO; autoresize = W+H; userInteractionEnabled = NO; layer = <CALayer: 0xac985d0>>

ios7.1:

<UISearchBar: 0xa4ef3e0; frame = (27 21; 290 44); text = ''; opaque = NO; autoresize = W+BM; gestureRecognizers = <NSArray: 0xa4f0e80>; layer = <CALayer: 0xa4ef6d0>>

   | <UIView: 0xa4f06f0; frame = (0 0; 290 44); clipsToBounds = YES; autoresize = W+H; layer = <CALayer: 0xa4f0750>>

   |    | <UISearchBarBackground: 0xa4f11b0; frame = (0 0; 290 44); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0xa4f1300>>

   |    | <UISearchBarTextField: 0xa4f1870; frame = (0 0; 0 0); text = ''; clipsToBounds = YES; opaque = NO; layer = <CALayer: 0xa4f1a80>>

   |    |    | <_UISearchBarSearchFieldBackgroundView: 0xa4f4880; frame = (0 0; 0 0); opaque = NO; autoresize = W+H; userInteractionEnabled = NO; layer = <CALayer: 0xa4f49e0>>

ios8.0beta:

<UISearchBar: 0x1405e140; frame = (27 21; 290 44); text = ''; opaque = NO; autoresize = W+BM; gestureRecognizers = <NSArray: 0x1405a650>; layer = <CALayer: 0x1405e3f0>>

   | <UIView: 0x14059ec0; frame = (0 0; 290 44); clipsToBounds = YES; autoresize = W+H; layer = <CALayer: 0x14059f30>>

   |    | <UISearchBarBackground: 0x1405a9d0; frame = (0 0; 290 44); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1405ab20>>

   |    | <UISearchBarTextField: 0x1405b0b0; frame = (0 0; 0 0); text = ''; clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x1405b2d0>>

   |    |    | <_UISearchBarSearchFieldBackgroundView: 0x140609b0; frame = (0 0; 0 0); opaque = NO; autoresize = W+H; userInteractionEnabled = NO; layer = <CALayer: 0x14060b10>>

从以上能够看出。在iOS7.0之前，UISearchbar视图里直接包括UISearchBarBackground和UISearchBarTextField两个视图，在iOS7.0及之后，UISearchbar视图里包括的是一个UIView视图，UIView视图里才是UISearchBarBackground和UISearchBarTextField两个视图。经多次试验，发现去除UISearchbar视图里的UISearchBarBackground后UISearchbar的背景就透明了，代码例如以下：

for (UIView *view in self.searchBar.subviews) {

    // for before iOS7.0

    if ([view isKindOfClass:NSClassFromString(@"UISearchBarBackground")]) {

        [view removeFromSuperview];

        break;

    }

    // for later iOS7.0(include)

    if ([view isKindOfClass:NSClassFromString(@"UIView")] && view.subviews.count > 0) {

        [[view.subviews objectAtIndex:0] removeFromSuperview];

        break;

    }

}

以上代码在iOS5/6/7/8.0beta下測试均有效，希望对须要使用UISearchBar的人有帮助。