HTML 属性中的 AngularJS 条件
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AngularJS conditionals in HTML Attribute
提问by Quang Van
How would you change an htmlattribute based on the model?
您将如何html根据模型更改属性？
I'm trying to change an input's placeholder text based on a length of an array:
我正在尝试根据数组的长度更改输入的占位符文本：
<input placeholder="{{todos.length ? 'Insert todo' : 'Insert your first todo'}}" />
But that doesn't seem to work...
但这似乎不起作用......
采纳答案by Ben Brandt
For anyone else who comes across this (like I just did via Google), it looks like Angular recently added support for the ternary operator in expressions. I just used it successfully in 1.2.16 to dynamically update a tooltip (title) attribute. It seems to have first appeared in the documentation for 1.2.17, although they still generally discourage its use:
对于遇到此问题的任何其他人（就像我刚刚通过 Google 所做的那样），看起来 Angular 最近在表达式中添加了对三元运算符的支持。我刚刚在 1.2.16 中成功使用它来动态更新工具提示（标题）属性。它似乎首先出现在 1.2.17 的文档中，尽管他们通常仍然不鼓励使用它：
From: AngularJS: Developer Guide: Expressions
Apart from the ternary operator (a ? b : c), you cannot write a control flow statement in an expression. The reason behind this is core to the Angular philosophy that application logic should be in controllers, not the views. If you need a real conditional, loop, or to throw from a view expression, delegate to a JavaScript method instead.
除了三元运算符 (a ? b : c)，您不能在表达式中编写控制流语句。这背后的原因是 Angular 哲学的核心，即应用程序逻辑应该在控制器中，而不是在视图中。如果您需要真正的条件、循环或从视图表达式中抛出，请改为委托给 JavaScript 方法。
回答by jaime
The ternary operator doesn't seem to work in this case, instead of doing this
三元运算符在这种情况下似乎不起作用，而不是这样做
{{cond ? true : false}}
Change it to
将其更改为
{{ exp && true || false }}
So your placeholderattribute would look like this (I have shortened it for demonstration purposes)
所以你的placeholder属性看起来像这样（为了演示目的，我缩短了它）
placeholder="{{todos.length > 0 && 'Insert' || 'Insert first'}}"
