如何在 iPhone / XCode 中定义静态字符串表？

Question

当我开发自定义手势时，我需要一个用于调试/跟踪消息的状态名称表。这个声明及其用法有什么问题？

static NSDictionary *dictStateNames = nil;

@implementation MyCustomGesture


@synthesize state;

+(void)initStateNames {
    if (dictStateNames == nil) {
        dictStateNames = [NSDictionary dictionaryWithObjectsAndKeys:
                          @"StateBegan", [NSNumber numberWithInt:UIGestureRecognizerStateBegan],
                          @"StateCancelled", [NSNumber numberWithInt:UIGestureRecognizerStateCancelled],
                          @"StateChanged", [NSNumber numberWithInt:UIGestureRecognizerStateChanged],
                          @"StateEnded", [NSNumber numberWithInt:UIGestureRecognizerStateEnded],
                          @"StateFailed", [NSNumber numberWithInt:UIGestureRecognizerStateFailed],
                          @"StatePossible", [NSNumber numberWithInt:UIGestureRecognizerStatePossible],
                          @"StateRecognized", [NSNumber numberWithInt:UIGestureRecognizerStateRecognized],
                          nil];
    }
}

-(id) init {
    self = [super init];
    if (self) {
        [MyCustomGesture initStateNames];
        state = UIGestureRecognizerStatePossible;
    }
    return self;
}

-(id) initWithTarget:(id)target action:(SEL)action {
    self = [super initWithTarget:target action:action];
    if (self) {
        [MyCustomGesture initStateNames];
        state = UIGestureRecognizerStatePossible;
    }
    return self;
}

+(NSString*) stateName: (UIGestureRecognizerState) state {
    NSString *retName = [dictStateNames objectForKey:[NSNumber numberWithInt:state]];
    if (retName == nil) {
        return [NSString stringWithFormat:@"Unknown state (%@)", state];
    } else {
        return retName;
    }
}

-(NSString*) currentStateName {
    return [MyCustomGesture stateName:state];
}

-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@"%s (%@): %@", __FUNCTION__, [self currentStateName], event);
}

Answer 1

当您将对象的引用存储在静态变量中时，您需要确保它不会被释放。因此，您可以向其发送 retain 消息，或者使用 alloc 而不是便捷的创建方法来创建。例如：

    dictStateNames = [[NSDictionary dictionaryWithObjectsAndKeys:
                      // List of objects and keys...
                      nil] retain];

或者这个...

    dictStateNames = [NSDictionary alloc] initWithObjectsAndKeys:
                      // List of objects and keys...
                      nil];

另外，您可以将 stateNames getter 和初始化代码合并到一个方法中，因此您通常会看到 Objective-C 开发人员编写如下方法

+ (NSDictionary *)stateNames
{
    static NSDictionary *stateNames;

    if (stateNames == nil) {
        stateNames = [NSDictionary alloc] initWithObjectsAndKeys:
                      // List of objects and keys...
                      nil];
    }

    return stateNames;
}

： ，没有必要在实例方法中调用它（无论如何这都是错误的，因为每次初始化实例时都会创建一个新字典，除非您以不同的方式处理它，否则前一个字典将会泄漏）。

在另一个（不相关的）注释中，请考虑重写您的 init 方法，如下所示：

- (id)init
{
    return [self initWithTarget:nil action:NULL];
}

Answer 2

[NSDictionary DictionaryWithObjectsAndKeys] 首先获取一个对象，然后是它的键（如方法名称所示），这看起来有点落后，但确实如此。