ios中UISearchBar的placeHolder左对齐

实现方法

重写UISearchBar，添加一个是否居中显示PlaceHolder的属性，然后利用NSMethodSignature这个类修改对齐的属性

@interfaceNSCodingSearchBar:UISearchBar/// 是否居中显示@property(nonatomic,assign, setter = setHasCentredPlaceholder:)BOOLhasCentredPlaceholder;@end

#pragma mark - Initializers// ------------------------------------------------------------------------------------------- (instancetype)initWithFrame:(CGRect)frame

{if((self= [superinitWithFrame:frame]))

{self.hasCentredPlaceholder=NO;

}returnself;

}// ------------------------------------------------------------------------------------------#pragma mark - Methods// ------------------------------------------------------------------------------------------- (void)setHasCentredPlaceholder:(BOOL)hasCentredPlaceholder

{

_hasCentredPlaceholder = hasCentredPlaceholder;

SEL centerSelector = NSSelectorFromString([NSStringstringWithFormat:@"%@%@", @"setCenter", @"Placeholder:"]);if([selfrespondsToSelector:centerSelector])

{

NSMethodSignature *signature = [[UISearchBarclass] instanceMethodSignatureForSelector:centerSelector];

NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];

[invocation setTarget:self];

[invocation setSelector:centerSelector];

[invocation setArgument:&_hasCentredPlaceholder atIndex:2];

[invocation invoke];

}

}@end