英文:
How to check length which can be null
问题
我想检查一下我的文本区域长度。
这是我的代码：
<div class="row d-flex justify-content-center textarea-wrapper">
<p class="mb-1">订单的附加信息：</p>
<textarea class="additionalInformation justify-content-center" name="additionalInformation" value="{{additionalInformation}}" formControlName="additionalInformation" placeholder="文本..."
[maxlength]="maxCharsOfArea"></textarea>
<span *ngIf="signupForm.controls['additionalInformation'].value.length">
{{signupForm.controls['additionalInformation'].value.length}} /{{maxCharsOfArea}}
</span>
</div>
视图：
在加载页面时，我收到错误消息无法读取 null 的属性（读取 'length'）。
添加任何文本后，一切正常运行。
我该如何在初始化时处理这个问题？
英文:
I would like to check out my textarea length.
This is my code:
<div class="row d-flex justify-content-center textarea-wrapper">
<p class="mb-1">Additional information to order:</p>
<textarea class=" additionalInformation justify-content-center" name="additionalInformation"
value="{{additionalInformation}}" formControlName="additionalInformation" placeholder="text..."
[maxlength]="maxCharsOfArea"></textarea>
<span *ngIf="signupForm.controls['additionalInformation'].value.length">
{{signupForm.controls['additionalInformation'].value.length}} /{{maxCharsOfArea}}</span>
</div>
View:
<br>
On Load my page I get error Cannot read properties of null (reading 'length')
After added any text, everything works perfect.
<br>
What Can I do with this in intialization?
答案1
得分: 2
在这种情况下，您应该能够使用安全导航运算符 ?. 来避免您收到的错误。
{{signupForm.controls['additionalInformation'].value?.length}} /{{maxCharsOfArea}}
如果您期望该值在初始化后保持为 null，您还可以添加一个空值合并运算符，将该值默认为 0。
{{signupForm.controls['additionalInformation'].value?.length ?? 0}} /{{maxCharsOfArea}}
https://docs.angular.lat/guide/template-expression-operators#safe-navigation-operator
英文:
In this case you should be able to use the safe navigation operator ?. to avoid the error you are receiving.
{{signupForm.controls['additionalInformation'].value?.length}} /{{maxCharsOfArea}}
https://docs.angular.lat/guide/template-expression-operators#safe-navigation-operator
If you expect that the value remains null after initialization, you could also add a nullish coalescing operator to default your value to 0
{{signupForm.controls['additionalInformation'].value?.length ?? 0}} /{{maxCharsOfArea}}
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