iOS11以下 searchbar占位文字居左

SEL centerSelector = NSSelectorFromString([NSString stringWithFormat:@"%@%@", @"setCenter", @"Placeholder:"]);
        if ([self respondsToSelector:centerSelector]) {
                    BOOL centeredPlaceholder = NO;
                    NSMethodSignature *signature = [[UISearchBar class] instanceMethodSignatureForSelector:centerSelector];
                    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
                    [invocation setTarget:self];
                    [invocation setSelector:centerSelector];
                    [invocation setArgument:&centeredPlaceholder atIndex:2];
                    [invocation invoke];
      }