在 Angular ng-if 表达式中使用 &（按位 AND 运算符）
[英]Using & (bitwise AND operator) in Angular ng-if expressions
问题描述
I can't get the & operator to work in an Angular ng-if expression (to use with some bit flags).
我无法让&运算符在 Angular ng-if表达式中工作（与某些位标志一起使用）。 Suppose we have some HTML like this:假设我们有一些这样的 HTML：
<div ng-if="value & 2"> </div>
If value equals 3, then the bitwise operation should return 2 and thus a true value.如果value等于 3，那么按位运算应该返回 2，因此是一个真值。
However, Angular throws a Syntax Error exception every time.但是，Angular 每次都会抛出Syntax Error异常。 Is the operation not allowed?不允许操作吗？ Or am I doing something wrong?还是我做错了什么？
Link to the plunker .链接到plunker 。
Edit: I already resolved my issue by using a simple function that does the job:编辑：我已经通过使用一个简单的函数来解决我的问题：
$scope.checkFlag = function(value, flag){
return value & flag;
}
But I really don't like this solution.但我真的不喜欢这个解决方案。 Is there a way to use it in an ng-if (without using the function, obviously)?有没有办法在ng-if使用它（显然不使用该函数）？
5 个解决方案
解决方案1
12 已采纳 2016-09-02 14:40:49
You cannot use the bitwise & operator in an Angular expression.您不能在 Angular 表达式中使用按位&运算符。 According to the documentation :根据文档：
Angular expressions are like JavaScript expressions with the following differences:
- ...
- You cannot use Bitwise,
,orvoidoperators in an Angular expression.,或void在角表达式运算符。If you want to run more complex JavaScript code, you should make it a controller method and call the method from your view.
A note on nomenclature: & is the bitwise AND operator;关于命名法的说明： &是按位与运算符； && is the logical AND operator. &&是逻辑与运算符。
UPDATE: Your checkFlag function is probably the best workaround because its name makes it clear what it does (and that's what I would use), but if you absolutely don't want an extra function, you can use the following equivalent expression:更新：您的checkFlag函数可能是最好的解决方法，因为它的名称清楚地表明了它的作用（这就是我将使用的），但是如果您绝对不想要额外的函数，则可以使用以下等效表达式：
<div ng-if="value % 4 >= 2"> </div>
In general, (value & x) != 0 (where x is a power of 2) is equivalent to value % (2 * x) >= x .通常， (value & x) != 0 （其中x是 2 的幂）相当于value % (2 * x) >= x 。
解决方案2
2 2021-02-19 11:08:16
One can accomplish this with a bitwise pipe:可以使用按位管道完成此操作：
import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
name: 'hasFlags'
})
export class HasFlagsPipe implements PipeTransform {
transform(flagsL: number, flagsR: number): boolean {
return (flagsL & flagsR) != 0;
}
}
Usage:用法：
<div [hidden]="flagsL | hasFlags : flagsR">
Note: I'm using angular 2+ but came across this post so hopefully this helps someone else.注意：我使用的是 angular 2+，但遇到了这篇文章，所以希望这对其他人有帮助。
解决方案3
1 2016-09-02 14:37:57
The problem is that you're using & instead of && .问题是您使用的是&而不是&& 。 & is the bitwise operator, and Angular doesn't allow bitwise operators in expressions. &是按位运算符，而 Angular 不允许在表达式中使用按位运算符。
解决方案4
1 2016-09-02 14:40:52
I am not sure what you want to accomplish here but you are using a bit-wise AND operator.我不确定您想在这里完成什么，但您正在使用按位 AND 运算符。 And in the angular documentation it says:在角度文档中，它说：
No Bitwise, Comma, And Void Operators: You cannot use Bitwise, , or void operators in an Angular expression.
解决方案5
1 2016-09-02 14:44:32
Since no one has provided a solution I'd assume you could just modify your html to:由于没有人提供解决方案，我认为您可以将 html 修改为：
<body ng-controller="MainCtrl">
<div ng-if="check(value,2)">Hey! </div>
</body>
with与
$scope.check = function(val, providedInt){
return val & providedInt;
};
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