html - Conditional pattern to be used along with required Angular7/8

Question

In my template driven form the textarea is required based on a condtion. I would also like the pattern to be conditional. I tried this syntax based on a question from angular 1.x but it doesn't seem to work. - pattern=" condition ? '.*[^ ].*' : ''" I also tried - pattern="condition ? (\s*[^\s]+\s*)+ : .*". is this possible with the later versions of Angular? Here is my stack blitz: https://stackblitz.com/edit/conditionalpattern

Answer 1

我认为如果你想传递一个表达式，你应该用方括号将模式括起来。但更重要的是，您不能pattern在标签中textareapattern使用该属性，因为textarea.

如MDN Web Docs中所述，

您不能提供特定的正则表达式来验证使用模式属性的值，就像您可以使用输入元素一样

因此，在您的情况下，我会使用input或考虑使用CustomValidator. 如果使用输入，请确保将表达式括在括号中：

<input type="text" [pattern]="condition ? pattern : noPattern">

这是一个带有输入字段工作示例的小型堆栈闪电战。

Answer 2

你想传递任何表达式吗？试试这个：<-input type="text" [pattern]="condition ? pattern : noPattern" >