extjs4.1中initComponent函数的用途是什么？

Question

谁能告诉我initComponentextjs4.1 中该函数的用途是什么？请举个例子

谢谢

Answer 1

该方法类似于constructor组件.它由true调用constructor,并且是一个非常好的钩点,用于自定义组件的初始化(如名称中所述!).

除非在极少数情况下,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合并到对象中.

假设您要自定义组件的配置,例如设置它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经传递了配置对象(以避免尝试设置属性undefined),并且您将覆盖配置对象,是不好的做法.如果您将选项设置为this,则可能会被配置对象覆盖.如果更改config对象中的值,则修改对象,从而破坏调用代码的期望(即重用config对象会产生意外结果).在initComponent,值永远是this.width,您不必担心配置.

另一个有趣的点是,创建initComponent子组件(用于容器),存储,视图,模板等的位置.因此,在调用超类initComponent方法之前,您可以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,没有进行渲染initComponent.已创建和配置子组件,但尚未创建其DOM元素.要影响渲染,您必须使用渲染相关事件或查找afterRender或onRender方法...

这是一个插图摘要:

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();
}