解決方法:新建一個UISearchBar的category，我這裡新建的名字為UISearchBar+ZMSearchBarPlaceholder

程式碼如下：

UISearchBar+ZMSearchBarPlaceholder.h

#import <UIKit/UIKit.h>
@interface UISearchBar (ZMSearchBarPlaceholder)
-(void)changeLeftPlaceholder:(NSString *)placeholder;
@end

UISearchB ar+ZMSearchBarPlaceholder.h

@implementation
 
 UISearchBar (ZMSearchBarPlaceholder)
-(void)changeLeftPlaceholder:(NSString *)placeholder {
    self.placeholder = placeholder;
    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];
    }
}
@end

然後呼叫該方法即可：

-(void)changeLeftPlaceholder:(NSString *)placeholder;

最後在工程中用到UISearchBar的類中匯入#UISearchBar+ZMSearchBarPlaceholder.h標頭檔案，