一个 绑定 定义了一个对象属性——源——与另一个对象属性（即目的地）之间的连接。

这种模式可以简化视图控制器，完全去除胶水代码的需求 - 更新视图自模型或相反的代码。它还可在模型层或视图层强制关系。

触发器

Cocoa 使用不同的方法来通知客户端值的变化：KVO、目标-动作、通知和委托。因此，绑定由多个 触发器 组成，其中触发器对其中任何一种方法做出响应。

以下是一个简单绑定的代码示例

// Set up the environment
UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Storyboard" bundle:nil];
RDPersonViewController *personVC = [storyboard instantiateInitialViewController];
personVC.person = [[Person alloc] initWithName:@"Jimmy"];
personVC.bindings = [[BNDBindings alloc] init];

// Define the source property
BNDProperty *sourceProperty = [[BNDProperty alloc] initWithObject:[personVC person] keyPath:@"name"];

// Define the destination property
BNDProperty *destinationProperty = [[BNDProperty alloc] initWithObject:[personVC textField] keyPath:@"text"];

// Create a bind from the source property to the destination property
BNDBinding *binding = [[BNDBinding alloc] initWithSourceProperty:sourceProperty destinationProperty:destinationProperty];

// Add a trigger to update the binding when KVO notifications are sent for person's name property
BNDTrigger *trigger = [[BNDKVOTrigger alloc] initWithKeyPath:@"name" object:[personVC person] delegate:binding];
[binding addTrigger:trigger];

// Add to the VC
[[personVC bindings] addBinding:binding];

上面的代码摘录不完整，因为没有反向绑定来确保人的名字与文本框的文本相匹配。然而，当 [UITextField name] 被修改时，UITextField 不发送 KVO 通知 - 相反，它发送一个 UITextFieldTextDidChangeNotification。

触发器可以在收到通知时更新绑定

// Create a binding as normal
BNDBinding *binding = [[BNDBinding alloc] initWithSource:[personVC textField] sourceKeyPath:@"text" destination:[personVC person] destinationKeyPath:@"name"];

// Create a trigger and add it to the binding
BNDTrigger *trigger = [[BNDNotificationTrigger alloc] initWithNotificationCenter:[NSNotificationCenter defaultCenter] notificationName:UITextFieldTextDidChangeNotification sender:[personVC textField] delegate:binding];
[binding addTrigger:trigger];

// Add it to the VC's bindings
[[personVC bindings] addBinding:binding];

当触发器收到 UITextFieldTextDidChangeNotification 时，它将使用新文本更新人的名字。

转换器

值通常需要从一种格式转换为另一种格式，特别是当从视图层传递到模型层时。您的用户界面组件可能认识到的数据格式与您的模型不同，例如，用户将数字输入到字符串中，而您的模型接受一个数字。一个 转换器 代替了属性对象，在值传递时进行转换。

------------       ---------------       -----------       ---------------       ------------
| Property |  -->  | Transformer |  -->  | Binding |  -->  | Transformer |  -->  | Property |
------------       ---------------       -----------       ---------------       ------------

转换器可以在值从源检索或分配到目的地时转换值——这无关紧要。在以下示例中，destinationProperty 预先定义为一个对象的属性

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
destinationProperty = [[BNDStringToNumberTransformer alloc] initWithProperty:destinationProperty numberFormatter:formatter];

destinationProperty 可以继续像定义对象属性一样处理。

可以通过用另一个转换器初始化转换器（而不是属性）进行转换器的链式调用，例如

transformer = [[CustomTransformer alloc] initWithProperty:transformer];

目前唯一的内置转换器是 BNLStringToNumberTransformer。欢迎提出建议和贡献力量。

安装

要将 Bindings 安装到您的项目中，将其添加到您的 Podfile 中：pod 'Bindings', '~> 0.2.0'。

许可证

Copyright (c) 2013 Ryan Davies

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