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AngularJS: API: ng/directive/ngIf

ngIf

  1. - directive in module ng

ngIf指令基于{表达式}来移除或重建DOM树的一部分。如果赋给 ngIf的表达式计算结果为假,元素会从DOM移除,其它情况会复制一份元素插入到DOM中。

ngIf 不同于 ngShowngHidengIf 是在DOM中完全移除或重建元素,而不是通过 display css 属性改变可见。一种常见的情况是,这种差异表现在依靠一个元素在DOM的位置使用CSS选择器时,例如 :first-child:last-child 伪类。

注意,当一个元素使用 ngIf 移除时,它的域会被销毁,并且当它恢复时一个新域会被创建。使用 ngIf 创建的域通过 原型继承继承它的父域。这个的重要含义是,如果在 ngIf 中使用ngModel会绑定到一个父域的javascript原始定义。这种情况下任何修改都会使子域的变化覆盖父域的值。

同时, ngIf使用自己编译状态来重建元素。 这种行为的一个例子是,如果一个元素的class属性在它编译后被直接修改,使用像 jQuery's .addClass() 方法等,并且元素之后被删掉。当ngIf 重建元素,class属性中已添加的类会丢失,因为会使用原始编译状态来重生成元素。

此外, 你可以通过 ngAnimate 模块来执行动画,控制 enterleave 的效果。

指令信息

  • 这个指令会创建新的作用域(scope)。
  • 这个指令执行优先级为600.

用法

  • 作为属性使用:
    <ANY
      ng-if="">
    ...
    </ANY>

动画

enter - 在ngIf内容改变时发生,并且一个新DOM元素会被创建和加入到ngIf容器中。

leave - 在ngIf内容从DOM移除时发生。

点击这里 了解更多关于涉及动画的步骤。

参数

参数 类型 详述
ngIf expression

如果表达式为假,元素从DOM树移除。如果为真,复制一份已编译过的元素添加到DOM树。

示例

index.html
Click me: <input type="checkbox" ng-model="checked" ng-init="checked=true" /><br/>
Show when checked:<span ng-if="checked" class="animate-if">
  I'm removed when the checkbox is unchecked.
</span>
animations.css
.animate-if {
  background:white;
  border:1px solid black;
  padding:10px;}

.animate-if.ng-enter, .animate-if.ng-leave {
  -webkit-transition:all cubic-bezier(0.250, 0.460, 0.450, 0.940) 0.5s;
  transition:all cubic-bezier(0.250, 0.460, 0.450, 0.940) 0.5s;}

.animate-if.ng-enter,.animate-if.ng-leave.ng-leave-active {
  opacity:0;}

.animate-if.ng-leave,.animate-if.ng-enter.ng-enter-active {
  opacity:1;}
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