如何在Angular(v9，Material)中导出或获取* ngFor循环的LOCAL变量 [英] How to export or get LOCAL variables of a *ngFor loop OUTSIDE it in Angular (v9, Material)
问题描述
Angular的第一步(版本9的Material).我正在使用以下代码创建表单:
First steps in Angular (with Material at version 9). I'm creating a form with the following code:
HTML:
<mat-form-field>
<mat-label>Course</mat-label>
<mat-select
[formControl]="subjectControl"
[attr.data-tag-subjectSemester]="this.subjectControl.value
? this.subjectControl.value.trim()
: ''
[attr.data-tag-subjectName]="this.subjectControl.value
? this.subjectControl.value.trim()
: ''
(selectionChange)="onChange($event)"
required
>
<mat-option>-- None --</mat-option>
<mat-optgroup *ngFor="let course of subjects" [label]="course.semester" [disabled]="course.disabled">
<mat-option *ngFor="let subject of course.courses" [value]="subject.subjectSemester"><!--For now, here I have to set `[value]` to `.subjectName` OR `.subjectSemester` to show it into the `data-tag`, but the question is How to export BOTH variables outside the `*ngFor` loop, if I can choose only one variable as option to show it as value?-->
{{ subject.subjectName }}
</mat-option>
</mat-optgroup>
</mat-select>
<mat-hint>
{{
this.subjectControl.value
? this.subjectControl.value.trim()
: ''
}}
</mat-hint>
</mat-form-field>
TS:
export interface SubjectGroup {
disabled?: boolean;
semester: string;
courses: Subject[];
}
export interface Subject {
subjectName: string;
subjectSemester: string;
}
subjectControl = new FormControl("", Validators.required);
export class FormComponent implements OnInit {
subjectControl = new FormControl("", Validators.required);
subjects: SubjectGroup[] = [
{
disabled: false,
semester: "Semester 1",
courses: [
{
subjectName: "Course 1",
subjectSemester: "1° Semester"
},
{
subjectName: "Course 2",
subjectSemester: "1° Semester"
},
{
subjectName: "Course 3",
subjectSemester: "1° Semester"
},
{
subjectName: "Course 4",
subjectSemester: "1° Semester"
},
{
subjectName: "Course 5",
subjectSemester: "1° Semester"
}
]
},
{
disabled: false,
semester: "Semester 2",
courses: [
{
subjectName: "Course 1",
subjectSemester: "2° Semester"
},
{
subjectName: "Course 2",
subjectSemester: "2° Semester"
},
{
subjectName: "Course 3",
subjectSemester: "2° Semester"
},
{
subjectName: "Course 4",
subjectSemester: "2° Semester"
}
]
}
];
}
onChange(event: { stopPropagation: () => void }) {
let subjectSemester = this.subjectControl.value; /* here I would to export both subjectName and subjectSemester; I tried in a way like `let subjectSemester = this.subjectControl.value?.subjectSemester;` and `let subjectName = this.subjectControl.value?.subjectName;`, but I can't get it! What I'm doing wrong?*/
alert(subjectSemester);
}
上面的代码没有向我返回正确的data-tag-subjectName属性，因为我在HTML代码的mat-option中将[value]设置为subject.subjectSemester.
The code above doesn't return me the correct data-tag-subjectName attribute, because I set [value] to subject.subjectSemester into the mat-option of my HTML code.
正如代码注释中所写，我想将subjectSemester和subjectName(属于 TS object的)subjectSemester和subjectName都导出到*ngFor循环之外，以例如，将它们存储在各自的数据属性(data-tag-subjectSemester和data-tag-subjectName)中，并在我的模板中将它们也用作label和/或mat-hint，但是由于某些原因我无法执行，例如:
As written in the code's comments, I would like to export outside the *ngFor loop both subjectSemester and subjectName (of the TS object) for the selected option, to store them in the respective data attributes (data-tag-subjectSemester and data-tag-subjectName), for example, and use also them in my template as label and/or mat-hint, but for some reason I can't do, for example:
TS:
onChange(event: { stopPropagation: () => void }) {
let subjectSemester = this.subjectControl.value?.subjectSemester;
let subjectName = this.subjectControl.value?.subjectName;
alert(subjectName + ", " + subjectSemester);
}
我尝试通过将mat-option用于mat-option的代码更改为HTML代码，将value导出为object来尝试选择所需的变量，就像上面修改的最后一个onChange函数一样，但是以此方式，我获得了undefined变量，因此表单中的空字段...
I tried to change the code by using [ngValue]="subject" for mat-option into the HTML code, to export the value as object to try to select the wanted variable like in the modified last onChange function above, but in this way I obtain undefined variables and so empty fields in my form...
理想情况下，我想使以下代码正常工作:
HTML:
<mat-form-field>
<mat-label>Course</mat-label>
<mat-select
[formControl]="subjectControl"
[attr.data-tag-subjectSemester]="this.subjectControl.value?.subjectSemester
? this.subjectControl.value?.subjectSemester.trim()
: ''
[attr.data-tag-subjectName]="this.subjectControl.value.?subjectName
? this.subjectControl.value?.subjectName.trim()
: ''
(selectionChange)="onChange($event)"
required
>
<mat-option>-- None --</mat-option>
<mat-optgroup *ngFor="let course of subjects" [label]="course.semester" [disabled]="course.disabled">
<mat-option *ngFor="let subject of course.courses" [value]="subject.subjectSemester">
{{ subject.subjectName }}
</mat-option>
</mat-optgroup>
</mat-select>
<mat-hint>
{{
this.subjectControl.value?.subjectSemester
? this.subjectControl.value?.subjectSemester.trim()
: ''
}}
</mat-hint>
</mat-form-field>
TS:
onChange(event: { stopPropagation: () => void }) {
let subjectSemester = this.subjectControl.value?.subjectSemester;
let subjectName = this.subjectControl.value?.subjectName;
alert(subjectName + ", " + subjectSemester);
}
希望了解我在做什么错，非常感谢.
Hope to understand what I'm doing wrong, thank you so much.
推荐答案
找到了解决方案，直到找到更好的解决方案为止:
Found a solution, until a better one:
HTML:
<mat-form-field>
<mat-label>Course</mat-label>
<mat-select
id="subjectSelector"
[formControl]="subjectControl"
(selectionChange)="onChange($event)"
required
>
<mat-option>-- None --</mat-option>
<mat-optgroup *ngFor="let course of subjects" [label]="course.semester" [disabled]="course.disabled">
<mat-option *ngFor="let subject of course.courses" [value]="subject.subjectSemester">
{{ subject.subjectName }}
</mat-option>
</mat-optgroup>
</mat-select>
</mat-form-field>
TS:
onChange(event: any) {
if (event.source.selected === undefined) {
document
.getElementById("subjectSelector")
.setAttribute("data-tag-subjectName", "subjectNone");
document
.getElementById("subjectSelector")
.setAttribute("data-tag-subjectSemester", "semesterNone");
} else {
let target = event.source.selected._element.nativeElement;
let selectedData = {
fieldId: target.getAttribute("id"),
Semester: event.value,
Name: target.innerText.trim()
};
//console.log(selectedData);
//alert(selectedData.Semester);
//alert(selectedData.Name);
document
.getElementById("subjectSelector")
.setAttribute(
"data-tag-subjectName", selectedData.Name.trim()
);
document
.getElementById("subjectSelector")
.setAttribute(
"data-tag-subjectSemester", selectedData.Semester.trim()
);
}
}
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