事实上，ng-if指令与ng-show指令不同，它创建了自己的作用域，导致了有趣的实际差异:

angular.module('app', []).controller('ctrl', function($scope){ $scope.delete = function(array, item){ array.splice(array.indexOf(item), 1); } }) <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script> <div ng-app='app' ng-controller='ctrl'> <h4>ng-if:</h4> <ul ng-init='arr1 = [1,2,3]'> <li ng-repeat='x in arr1'> {{show}} <button ng-if='!show' ng-click='show=!show'>Delete {{show}}</button> <button ng-if='show' ng-click='delete(arr1, x)'>Yes {{show}}</button> <button ng-if='show' ng-click='show=!show'>No</button> </li> </ul> <h4>ng-show:</h4> <ul ng-init='arr2 = [1,2,3]'> <li ng-repeat='x in arr2'> {{show}} <button ng-show='!show' ng-click='show=!show'>Delete {{show}}</button> <button ng-show='show' ng-click='delete(arr2, x)'>Yes {{show}}</button> <button ng-show='show' ng-click='show=!show'>No</button> </li> </ul> <h4>ng-if with $parent:</h4> <ul ng-init='arr3 = [1,2,3]'> <li ng-repeat='item in arr3'> {{show}} <button ng-if='!show' ng-click='$parent.show=!$parent.show'>Delete {{$parent.show}}</button> <button ng-if='show' ng-click='delete(arr3, x)'>Yes {{$parent.show}}</button> <button ng-if='show' ng-click='$parent.show=!$parent.show'>No</button> </li> </ul> </div>

在第一个列表，on-click事件，显示变量，从内部/自己的作用域，被改变了，但ng-if正在观察从外部作用域同名的另一个变量，所以解决方案不工作。对于ng-show，我们只有一个show变量，这就是它工作的原因。要修复第一次尝试，我们应该通过$parent.show引用show from parent/outer scope。

ngIf通过删除或重新创建元素对DOM进行操作。

而ngShow应用css规则来隐藏/显示内容。

对于大多数情况(并非总是如此)，我将总结为，如果你需要一次检查来显示/隐藏东西，使用ng-if，如果你需要根据屏幕上的用户操作显示/隐藏东西(比如选中复选框然后显示文本框，未选中然后隐藏文本框等)，那么使用ng-show

事实上，ng-if指令与ng-show指令不同，它创建了自己的作用域，导致了有趣的实际差异:

angular.module('app', []).controller('ctrl', function($scope){ $scope.delete = function(array, item){ array.splice(array.indexOf(item), 1); } }) <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script> <div ng-app='app' ng-controller='ctrl'> <h4>ng-if:</h4> <ul ng-init='arr1 = [1,2,3]'> <li ng-repeat='x in arr1'> {{show}} <button ng-if='!show' ng-click='show=!show'>Delete {{show}}</button> <button ng-if='show' ng-click='delete(arr1, x)'>Yes {{show}}</button> <button ng-if='show' ng-click='show=!show'>No</button> </li> </ul> <h4>ng-show:</h4> <ul ng-init='arr2 = [1,2,3]'> <li ng-repeat='x in arr2'> {{show}} <button ng-show='!show' ng-click='show=!show'>Delete {{show}}</button> <button ng-show='show' ng-click='delete(arr2, x)'>Yes {{show}}</button> <button ng-show='show' ng-click='show=!show'>No</button> </li> </ul> <h4>ng-if with $parent:</h4> <ul ng-init='arr3 = [1,2,3]'> <li ng-repeat='item in arr3'> {{show}} <button ng-if='!show' ng-click='$parent.show=!$parent.show'>Delete {{$parent.show}}</button> <button ng-if='show' ng-click='delete(arr3, x)'>Yes {{$parent.show}}</button> <button ng-if='show' ng-click='$parent.show=!$parent.show'>No</button> </li> </ul> </div>

在第一个列表，on-click事件，显示变量，从内部/自己的作用域，被改变了，但ng-if正在观察从外部作用域同名的另一个变量，所以解决方案不工作。对于ng-show，我们只有一个show变量，这就是它工作的原因。要修复第一次尝试，我们应该通过$parent.show引用show from parent/outer scope。

ngIf

ngIf指令根据表达式删除或重新创建DOM树的一部分。如果赋给ngIf的表达式求值为false，则该元素将从DOM中移除，否则该元素的克隆将重新插入DOM中。

<!-- when $scope.myValue is truthy (element is restored) -->
<div ng-if="1"></div>

<!-- when $scope.myValue is falsy (element is removed) -->
<div ng-if="0"></div>

当使用ngIf删除一个元素时，它的作用域将被破坏，当元素恢复时将创建一个新的作用域。ngIf中创建的作用域使用原型继承继承父作用域。

如果ngIf中使用ngModel绑定到父作用域中定义的JavaScript原语，那么对子作用域中变量的任何修改都不会影响父作用域中的值。

<input type="text" ng-model="data">
<div ng-if="true">
    <input type="text" ng-model="data">
</div>        

为了避免这种情况，并从子范围内更新父范围内的模型，使用一个对象:

<input type="text" ng-model="data.input">
<div ng-if="true">
    <input type="text" ng-model="data.input">
</div>

或者，$parent变量引用父作用域对象:

<input type="text" ng-model="data">
<div ng-if="true">
    <input type="text" ng-model="$parent.data">
</div>

ngShow

ngShow指令根据提供给ngShow属性的表达式来显示或隐藏给定的HTML元素。通过在元素上删除或添加ng-hide CSS类来显示或隐藏元素。.ng-hide CSS类是在AngularJS中预定义的，它将显示样式设置为none(使用!重要标志)。

<!-- when $scope.myValue is truthy (element is visible) -->
<div ng-show="1"></div>

<!-- when $scope.myValue is falsy (element is hidden) -->
<div ng-show="0" class="ng-hide"></div>

当ngShow表达式的值为false时，ng-hide CSS类被添加到元素的class属性中，使其变为隐藏状态。当为true时，ng-hide CSS类将从元素中移除，使元素不显示为隐藏状态。

ng-if指令从页面中删除内容，ng-show/ng-hide使用CSS的display属性隐藏内容。

如果您想使用:first-child和:last-child伪选择器来设置样式，这是非常有用的。

也许有趣的一点是，两者的优先级不同。

据我所知，ng-if指令是所有Angular指令中优先级最高(如果不是最高的话)的指令之一。这意味着:它将在所有其他低优先级的指令之前运行。事实上，它首先运行，意味着有效地，在任何内部指令被处理之前，元素被删除。至少，我是这么认为的。

I observerd and used this in the UI I'm building for my current customer. The entire UI is quite heavily packed, and it had ng-show and ng-hide all over it. Not to go into too much detail, but I built a generic component, which could be managed using JSON config, so I had to do some switching inside the template. There is an ng-repeat present, and inside the ng-repeat, a table is shown, which has a lot of ng-shows, ng-hides and even ng-switches present. They wanted to show at least 50 repeats in the list, which would result in more or less 1500-2000 directives to be resolved. I checked the code, and the Java backend + custom JS on the front would take about 150ms to process the data, and then Angular would chew some 2-3 seconds on it, before displaying. The customer did not complain, but I was appalled :-)

In my search, I stumbled across the ng-if directive. Now, maybe it's best to point out that at the point of conceiving this UI, there was no ng-if available. Because the ng-show and ng-hide had functions in them, which returned booleans, I could easily replace them all with ng-if. By doing so, all inner directives seemed to be no longer evaluated. That meant that I dropped back to about a third of all directives being evaluated, and thus, the UI speeded up to about 500ms - 1 sec loading time. (I have no way to determine exact seconds)

注意:指令没有被评估的事实，是对下面发生的事情的一个有根据的猜测。

所以，在我看来:如果你需要元素出现在页面上(即:检查元素，或其他)，但只是被隐藏，请使用ng-show/ng-hide。在所有其他情况下，使用ng-if。