参考：ON IOS 7 UISEARCHBAR LEFT ALIGN PLACEHOLDER TEXT?

1 @interface NSCodingSearchBar : UISearchBar2  3 // Default by the system is YES.4 // https://github.com/nst/iOS-Runtime-Headers/blob/master/Frameworks/UIKit.framework/UISearchBar.h5 @property (nonatomic, assign, setter = setHasCentredPlaceholder:) BOOL hasCentredPlaceholder;6  7 @end

 1 @implementation NSCodingSearchBar 2   3   4 // ------------------------------------------------------------------------------------------ 5 #pragma mark - Initializers 6 // ------------------------------------------------------------------------------------------ 7 - (instancetype)initWithFrame:(CGRect)frame 8 { 9     if ((self = [super initWithFrame:frame]))10     {11         self.hasCentredPlaceholder = YES;12     }13     14     return self;15 }16  17  18 // ------------------------------------------------------------------------------------------19 #pragma mark - Methods20 // ------------------------------------------------------------------------------------------21 - (void)setHasCentredPlaceholder:(BOOL)hasCentredPlaceholder22 {23     _hasCentredPlaceholder = hasCentredPlaceholder;24     25     SEL centerSelector = NSSelectorFromString([NSString stringWithFormat:@"%@%@", @"setCenter", @"Placeholder:"]);26     if ([self respondsToSelector:centerSelector])27     {28         NSMethodSignature *signature = [[UISearchBar class] instanceMethodSignatureForSelector:centerSelector];29         NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];30         [invocation setTarget:self];31         [invocation setSelector:centerSelector];32         [invocation setArgument:&_hasCentredPlaceholder atIndex:2];33         [invocation invoke];34     }35     36 }37  38  39 @end