是否有必要覆盖bind:toObject:withKeyPath:options:在NSView子类中实现绑定？

Question

我有一个NSView子类,它具有我想要绑定的属性.我在子类中实现了以下内容:

myView.h:

@property (readwrite, retain) NSArray *representedObjects;

myView.m:

@synthesize representedObjects;

+(void)initialize
{
    [self exposeBinding: @"representedObjects"];
}


-(void)bind:(NSString *)binding toObject:(id)observableController withKeyPath:(NSString *)keyPath options:(NSDictionary *)options
{
    if ([binding isEqualToString:@"representedObjects"]) {
        [observableController addObserver: self forKeyPath:@"arrangedObjects" options:NSKeyValueChangeNewKey context:nil];
    } else {
        [super bind: binding toObject:observableController withKeyPath:keyPath options: options];
    }
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"arrangedObjects"]) {
        [self setRepresentedObjects: [object arrangedObjects]];
    }
}

然后我创建了对arrayController的绑定-[AppController awakeFromNib]:

[myView bind:@"representedObjects" toObject:arrayController withKeyPath:@"arrangedObjects" options: nil];

这是实现绑定的正确方法吗？它涉及很多锅炉板代码,这让我觉得我做错了.

我认为NSObject会自动实现我手动完成的工作,-bind:toObject:withKeyPath:options:但事实并非如此.如果我注释掉我-bind:toObject:withKeyPath:options:的setRepresentedObjects方法永远不会被调用.

附加信息:我已经做了一些更多的调查,并得出结论我的原始方法是正确的,你必须超越-bind:toObject:withKeyPath:options:.以下是Cocoa Bindings编程主题:绑定如何工作的引用？:

在其bind:toObject:withKeyPath:options:方法中,对象必须至少执行以下操作:

• 确定要设置的绑定
• 使用什么键路径和哪些选项记录它绑定到的对象
• 注册为绑定对象的keypath的观察者,以便它接收更改通知

清单2中的代码示例显示了Joystick的bind的部分实现:toObject:withKeyPath:options:仅处理角度绑定的方法.

清单2部分实现bind:toObject:withKeyPath:Joystick类的options方法:

static void *AngleBindingContext = (void *)@"JoystickAngle";

- (void)bind:(NSString *)binding
 toObject:(id)observableObject
 withKeyPath:(NSString *)keyPath
 options:(NSDictionary *)options
{
 // Observe the observableObject for changes -- note, pass binding identifier
 // as the context, so you get that back in observeValueForKeyPath:...
 // This way you can easily determine what needs to be updated.

if ([binding isEqualToString:@"angle"])
 {
    [observableObject addObserver:self
                   forKeyPath:keyPath
                  options:0
                  context:AngleBindingContext];

    // Register what object and what keypath are
    // associated with this binding
    observedObjectForAngle = [observableObject retain];
    observedKeyPathForAngle = [keyPath copy];

    // Record the value transformer, if there is one
    angleValueTransformer = nil;
    NSString *vtName = [options objectForKey:@"NSValueTransformerName"];
    if (vtName != nil)
    {
        angleValueTransformer = [NSValueTransformer
            valueTransformerForName:vtName];
    }
 }
 // Implementation continues...

这清楚地表明Joystick类(它是一个NSView子类)需要覆盖-bind:toObject:withKeyPath:options:.

我觉得这很令人惊讶.我对此结论持怀疑态度,因为我没有找到其他代码示例.但是,正如苹果公司的官方文档说我应该过度使用,-bind:toObject:withKeyPath:options:我得出结论认为这是正确的方法.

如果有人能证明我错了,我会很高兴的!

Answer 1

不，您不应该\xe2\x80\x99 需要该粘合代码。

\n\n

\xe2\x80\x9cdoesn\xe2\x80\x99t 似乎是这样\xe2\x80\x9d 是什么意思？如果忽略它会发生什么？

\n