Comments (5)
changes 是一个 SimpleChanges 类型对象,changes 里面有 questionnaire 这个 SimpleChange 类型的子对象,注意"s"结尾的区别。
questionnaire 是一个对象,不是一个方法
from angular2-questionnaire.
老师说还没注意到有没‘s’,谢谢啦。然后后来自己也debugger了一下,现在比较明白了。然后里面的github的代码存在着这么一个bug:
ngOnChanges(changes: SimpleChanges){
let questionnaireChange = changes['questionnaire'];
if( questionnaireChange.previousValue.state &&
questionnaireChange.currentValue.state !== questionnaireChange.previousValue.state){
this.questionnaire = changes['questionnaire'].currentValue;
this.setState();
}
}
这段代码中,当第一次调用到ngOnChanges的时候questionnaireChange.previousValue为undefined,所以调用questionnaireChange.previousValue.state会报错,感觉原本的代码意图应该是
if( questionnaireChange.previousValue&&
questionnaireChange.currentValue.state !== questionnaireChange.previousValue.state)
还有一点想请教下。changes所拥有对象的名称是根据@input来判断的?理由是OnChanges是用来在@input的值变化时调用的钩子?不知怎么理解对不对
from angular2-questionnaire.
恩,谢谢反馈问题。
from angular2-questionnaire.
OnChanges的参数值是根据@input定义的,当@input() 修饰的变量发生变化就会触发 OnChanges钩子
from angular2-questionnaire.
想明白了。谢谢
from angular2-questionnaire.
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