extjs4.1中initComponent函数有什么用？

Question

谁能告诉我initComponent 函数在extjs4.1 中的用途是什么？请举个例子

谢谢

Answer 1

此方法类似于组件的constructor。它由真正的constructor 调用，是一个非常好的自定义组件初始化的挂钩点（正如名字所说！）。

除了在极少数情况下，您应该覆盖initComponent 而不是constructor，因为更基本的初始化已经发生。最值得注意的是，传递给构造函数的配置对象已经被合并到对象中。

假设您要自定义组件的配置，例如设置其width。如果您尝试在构造函数中执行此操作，则必须首先检查我们是否已通过配置对象（以避免尝试在undefined 上设置属性），并且您将拥有覆盖配置对象，这是不好的做法。如果您在this 中设置选项，它可能会被配置对象覆盖。如果更改 config 对象中的值，则会修改对象，从而破坏调用代码的预期（即重用 config 对象将产生意想不到的结果）。在initComponent中，值永远是this.width，你不用担心配置。

另一个有趣的点是initComponent 是创建子组件（用于容器）、商店、视图、模板等的地方。因此，在调用超类 initComponent 方法之前，您可以对它们采取行动，确保它们尚未被使用或需要（例如，添加项目、创建商店等）。另一方面，一旦调用了 super 方法，就可以保证所有这些依赖项都已创建并实例化。例如，这是向依赖项添加侦听器的好地方。

话虽如此，请记住initComponent 中没有进行任何渲染。子组件已创建和配置，但它们的 DOM 元素尚未创建。要影响渲染，您必须使用渲染相关事件或查找 afterRender 或 onRender 方法...

这是一个图解摘要：

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();
}