extjs4.1中的initComponent函数有什么用途？

Question

有人能告诉我在extjs4.1中，initComponent函数的作用是什么？请提供一个例子。

谢谢。

- mohan

Answer 1

这个方法类似于组件的constructor。它由真正的constructor调用，并且是一个非常好的挂钩点，用于自定义组件的初始化（正如名称中所说的那样！）。

除非在某些非常罕见的情况下，你应该重写initComponent而不是constructor，因为更基本的初始化已经完成。特别是，在构造函数中传递给配置对象的合并到对象中。

假设您想自定义组件的配置，例如设置其width。如果您尝试在构造函数中执行此操作，则必须首先检查是否已传递了配置对象（以避免尝试在undefined上设置属性），并且您将覆盖配置对象，这是不良实践。如果您在this中设置选项，则可能会被配置对象覆盖。如果您更改配置对象中的值，则修改对象，从而破坏调用代码的期望（即重用配置对象将产生意外结果）。在initComponent中，该值始终为this.width，您不必担心配置。

另一个有趣的观点是，initComponent是创建子组件（对于容器）、存储、视图、模板等的地方。因此，在调用超类initComponent方法之前，您可以对这些进行操作，确保它们尚未被使用或需要（例如添加项目、创建存储等）。另一方面，一旦调用了超级方法，就可以保证所有这些依赖项都已创建和实例化。因此，这是添加依赖项侦听器的好地方。

话虽如此，请记住，在initComponent中不会进行任何渲染。子组件已经创建和配置，但是它们的DOM元素还没有创建。要影响渲染，您必须使用与渲染相关的事件或查找afterRender或onRender方法...

下面是一个详细说明：

constructor: function(config) {

    // --- Accessing a config option is very complicated ---

    // unsafe: this may be changed by the passed config
    if (this.enableSomeFeature) { ... }

    // instead, you would have to do:
    var featureEnabled;
    if (config) { // not sure we've been passed a config object
        if (Ext.isDefined(config.featureEnabled)) {
            featureEnabled = config.featureEnabled;
        } else {
            featureEnabled = this.enableSomeFeature;
        }
    } else {
        featureEnabled = this.enableSomeFeature;
    }
    // now we know, but that wasn't smooth
    if (featureEnabled) {
        ...
    }


    // --- Even worse: trying to change the value of the option ---

    // unsafe: we may not have a config object
    config.enableSomeFeature = false;

    // unsafe: we are modifying the original config object
    (config = config || {}).enableSomeFeature = false;

    // cloning the config object is safe, but that's ineficient
    // and inelegant
    config = Ext.apply({enableSomeFeature: false}, config);


    // --- Super method ---

    this.callParent(arguments); // don't forget the arguments here!

    // --------------------

    // here initComponent will have been called
}

,initComponent: function() {

    // --- Accessing config options is easy ---

    // reading
    if (this.enableSomeFeature) { ... }

    // or writing: we now we change it in the right place, and
    // we know it has not been used yet
    this.deferRender = true;


    // --- Completing or changing dependant objects is safe ---
    // items, stores, templates, etc.

    // Safe:
    // 1. you can be sure that the store has not already been used
    // 2. you can be sure that the config object will be instantiated
    //    in the super method
    this.store = {
        type: 'json'
        ...
    };


    // --- However that's too early to use dependant objects ---

    // Unsafe: you've no certitude that the template object has
    // already been created
    this.tpl.compile();


    // --- Super method ---

    this.callParent();

    // --------------------


    // Safe: the store has been instantiated here
    this.getStore().on({
        ...
    });


    // will crash, the element has not been created yet
    this.el.getWidth();
}

- rixo