我刚刚开始使用Aurelia框架学习Typescript。我已经在Aurelia的Todo应用程序中使用ViewEngineHooks在Aurelia模板中实现了Matthew Davis的博客TypeScript Enums http://davismj.me/blog/template-constants/。
我想将默认枚举值设置为列表中的第二个值,并将默认值设置为列表中的第一个值。
另外,我想知道{待办事项,优先级}或仅{待办事项}是否需要导入,如待办事项列表所示。
待办事项
// Pro Tip: By starting our enum at 1, we ensure that all values in the enum are truthy.
export enum Priority {
High = 1,
Medium,
Low
}
export class Todo {
@observable done;
//*** Setting priority: Priority = 2 OR priority: Priority = Priority.Medium - Does not change the default from High / 1 ***
//constructor(public list: TodoList, public description: string, public priority: Priority = 2, public editing: boolean = false) {
constructor(public list: TodoList, public description: string, public priority: Priority = Priority.Medium, public editing: boolean = false) {
this.list = list;
this.description = description;
//*** Setting this.priority = 2 OR this.priority = Priority.Medium - Does not change the default from High / 1 ;
//this.priority = 2;
this.priority = Priority.Medium;
this.editing = false;
}
todo-list.ts
//*** Is {Todo} OR {Todo, Priority} needed for importing? ***
//import {Todo} from './todo';
import {Todo, Priority} from './todo';
...
add(description) {
if (description) {
//*** Setting (this, description, 2) OR (this, description, Priority.Medium) - Does not change the default from High / 1 ***
//this.todos.push(new Todo(this, description, 2));
this.todos.push(new Todo(this, description, Priority.Medium));
this.invalidateView();
}
}
待办事项.html
<select id="priority" value.bind="type">
<option value.bind="Priority[type]" repeat.for="type of Prioritys">${type}</option>
</select>
据我所知,在声明变量时,您无法设置枚举的默认值,就像数字或布尔值没有默认值一样。 但是,您可以定义函数参数的默认值,就像在构造函数 (priority: Priority = Priority.Medium
中所做的那样,这样在调用构造函数时就不必提供该参数。
另外两个注意事项: 不应该是this.priority = priority; this.editing = editing;
而不是this.priority = Priority.Medium; this.editing = false;
吗?其次,如果您将public
放在参数前面,则会自动添加并分配类属性,因此您不需要构造函数的附加行。但是,对于更复杂的类,我可能会手动创建和分配属性。
关于你的第二个问题:你需要在引用该枚举后立即导入Priority
,例如在编写Priority.Medium
时。例如,当您在不使用枚举名称的情况下比较Priority
类型的两个不同属性时,您不必导入它(例如this.todos[0].priority === this.todos[1].priority
(。
在<option>
s 上使用model.bind
没有任何更改的原因是因为正确的值尚未"分配"给<option>
。为此,您需要使用model
属性。
<select id="priority" value.bind="type">
<option model.bind="Priority[type]" repeat.for="type of Priorities">
${type}
</option>
</select>