为什么我们不能将插值表达式与"ng-model"一起使用?但可以与"ng-src"一起使用吗? [英] Why can't we use interpolation expression with "ng-model" but can use with "ng-src"?

问题描述

我正在尝试将插值表达式与ng-model指令一起使用，但是它不起作用.相反，当我将插值与ng-src一起使用时，它可以很好地工作.这有什么区别?

I am trying to use the interpolation expression with the ng-model directive but it doesn't work. On the contrary, when I use interpolation with ng-src, it works perfectly fine. What is this difference due to?

推荐答案

这完全取决于指令的设置方式.

It all depends upon how the directive has been setup.

ng-model，ng-show和ng-click之类的某些指令不使用插值符号，而指令ng-src则采用插值符号.

Some directives like ng-model, ng-show and ng-click do not use interpolation symbols whereas directives ng-src take interpolation.

仅适用于字符串的指令支持插值.如果我们看一下ng-src的实现，您会发现

Interpolation are supported on directives that work only with strings. If we look at ng-src implementation you will find

 attr.$observe(normalized, function(value) {
          if (!value)
             return;

          attr.$set(attrName, value);

          if (msie) element.prop(attrName, attr[attrName]);
        });

attr.$observe监视属性而不是模型的更改.模型更改会导致属性更改(由于插值)，从而导致触发触发器.

attr.$observe watches for change in attribute not model. Model changes cause attribute changes (due to interpolation), hence causing the trigger to fire.

对于所有其他指令，例如ng-model，属性值是一个在当前范围内求值的表达式，并不限于字符串值.

For all other directives like ng-model, the attribute value is an expression which is evaluated in current scope and is not limited to string value.

如果您要开发自己的指令，则隔离范围属性=和@可以帮助您实现类似的目标.

If you are developing your own directives, isolated scope properties = and @ help you achieve something similar.

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