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The editor will share with you an example analysis of the Hook mechanism in Flex. I hope you will gain something after reading this article. Let's discuss it together.

In the previous article, we briefly introduced the Flex-based interface composition SDK, which uses the Hook mechanism to implement UI Part lifecycle management, Master-Details relationship building, and UI Part injection. Hook is a hook, which can be understood as adding additional functions to an object in a transparent way, so as to achieve transparent extension. Hook mechanism can be applied to all kinds of platforms, regardless of language, and it conveys an idea. The advantage of using the Hook mechanism to implement these functions is that it provides these functions without increasing the complexity of the user, and it is fully compatible with the design based on Flex components, so that users have no idea that we are using SDK. In other words, with the introduction of this Hook mechanism, the functionality provided by the SDK is completely transparent to developers, which is cool. However, no solution is *. This Hook mechanism needs to be controlled in a certain order during resource release and event capture, which requires high requirements for SDK maintainers. If you don't pay attention, inexplicable errors will occur. In addition, the Hook mechanism is a little more difficult to implement.

The following figure is a class diagram of the Hook mechanism implementation.

IDisposable interface draws lessons from Microsoft memory management model, Adobe Flex is very rough in memory management and GC, and there are a lot of SDK memory leaks, especially in modular applications. Therefore, when I designed the SDK, I introduced some of Microsoft's memory management ideas, but made a few changes as needed. The SDK memory release is divided into two phases: * the preDispose function is implemented to release dependencies between class instances, and the second phase is the postDispose function implementation, which is used to release instance references. All Hook implement the IDisposable interface, which can achieve memory release.

IComponentHook inherits from the IDisposable interface and defines a basic interface of Hook, which is composed of compositionManager, component, isHooked properties and hook, unHook methods, which are used to represent the composition manager, the components mounted by Hook, whether to mount and unmount, and to unmount.

ComponentHook is all the Hook base classes, it directly implements the definition of compositionManager, component, isHooked properties, and sets the mounted component and isHooked properties in the hook method and unHook method.

The lifecycle management function consists of IComponentLifecycleHook, IContainerLifecycleHook interfaces and ComponentLifecycleHook, ContainerLifecycleHook, ViewStackLifecycleHook implementation classes. ComponentLifecycleHook is used to save the lifecycle state of a leaf control, which is determined by its container. ContainerLifecycleHook is used to save the lifecycle state of the container and to manage the state of child controls. By default, all child controls are consistent with the state of the container. ViewStack is a special container that displays only one child control at any one time. ViewStackLifecycleHook is used to save the state of the ViewStack container and manage the state of the currently displayed control. When the ViewStack state changes, only the currently selected child control is changed, while the other child controls are inactive.

SmartPartPlaceHolderHook and SmartPartContainerHook implement UI Part dynamic injection (in SDK, each UI Part is named SmartPart, named after Microsoft CAB). These two Hook are containers that implement the ISmartPartPlaceHolder and ISmartPartContainer interfaces, read the location property from such containers, then get the corresponding SmartPart from SmartPartManager based on the location attribute, and then inject it into these containers. SmartPartPlaceHolder differs from SmartPartContainer in that the former can inject only one SmartPart, while the latter can inject multiple SmartPart.

DetailsSmartPartHook implements Master-Details relationship construction, adding its masterSmartPartLocations corresponding MasterSmartPart to a component that implements the IDetailsSmartPart interface, and establishing a relationship between the two. The establishment of this relationship is transparent for use.

ComponentTreeHook is the core class of Hook mechanism, which is mounted to the root node of the control tree, dynamically listens to the onChildAdded/Removed events of the entire control tree, and realizes the creation and destruction of all Hook of the entire control tree; DebugComponentTreeHook inherits from ComponentTreeHook, but it is different from it in that it collects debugging information of the entire control tree, which can be automatically displayed to the following DebugPanel.

After reading this article, I believe you have some understanding of "sample Analysis of Hook Mechanism in Flex". If you want to know more about it, you are welcome to follow the industry information channel. Thank you for reading!

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