Typescript 和 React 使用空类型数组设置初始状态
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Typescript and React setting initial state with empty typed array
提问by Vlives
Say I have the following snippet:
假设我有以下代码段：
interface State {
alarms: Alarm[];
}
export default class Alarms extends React.Component<{}, State> {
state = {
alarms: []
};
Since I am trying to set alarms: []Typescript doesn't like it, as [] != Alarm[]. I found that I can use alarms: new Array<Alarm>()which initializes an empty typed array, however I don't really like this syntax - is there an easier/better approach?
由于我试图设置alarms: []Typescript 不喜欢它，因为[] != Alarm[]. 我发现我可以使用alarms: new Array<Alarm>()which 初始化一个空类型的数组，但是我真的不喜欢这种语法 - 有更简单/更好的方法吗？
回答by Titian Cernicova-Dragomir
The problem is that when you create a field in a class the compiler will type that field accordingly (either using the explicit type or an inferred type from the initialization expression such as in your case).
问题是，当您在类中创建字段时，编译器将相应地键入该字段（使用显式类型或从初始化表达式中推断出的类型，例如在您的情况下）。
If you want to redeclare the field, you should specify the type explicitly :
如果要重新声明该字段，则应明确指定类型：
export default class Alarms extends React.Component<{}, State> {
state: Readonly<State> = {
alarms: []
};
}
Or set the state in the constructor:
或者在构造函数中设置状态：
export default class Alarms extends React.Component<{}, State> {
constructor(p: {}) {
super(p);
this.state = {
alarms: []
};
}
}
You could also cast the array to the expected type, but if there are a lot of fields it would be better to let the compiler check the object literal for you.
您也可以将数组转换为预期的类型，但如果有很多字段，最好让编译器为您检查对象文字。
回答by Air1
Would
将
alarms: [] as Alarm[]
alarms: [] as Alarm[]
work for Typescript and for you ?
为 Typescript 和你工作？
See this question on how you can cast arrays in Typescript : TypeScript casting arrays
请参阅有关如何在 Typescript 中转换数组的问题：TypeScript cast arrays
回答by rahulnikhare
Declaration:
宣言：
alarms: Array<Alarm>
alarms: Array<Alarm>
Initialization in state :
状态初始化：
this.setState({
var1:'',
var2:''
});
I prefer the above declaration
我更喜欢上面的声明
