只需从Angular 8中添加新的更新。

For case if with else, we can use ngIf and ngIfElse. <ng-template [ngIf]="condition" [ngIfElse]="elseBlock"> Content to render when condition is true. </ng-template> <ng-template #elseBlock> Content to render when condition is false. </ng-template> For case if with then, we can use ngIf and ngIfThen. <ng-template [ngIf]="condition" [ngIfThen]="thenBlock"> This content is never showing </ng-template> <ng-template #thenBlock> Content to render when condition is true. </ng-template> For case if with then and else, we can use ngIf, ngIfThen, and ngIfElse. <ng-template [ngIf]="condition" [ngIfThen]="thenBlock" [ngIfElse]="elseBlock"> This content is never showing </ng-template> <ng-template #thenBlock> Content to render when condition is true. </ng-template> <ng-template #elseBlock> Content to render when condition is false. </ng-template>

<div *ngIf="this.model.SerialNumber != '';then ConnectedContent else DisconnectedContent" class="data-font">    </div>

<ng-template #ConnectedContent class="data-font">Connected</ng-template>
<ng-template #DisconnectedContent class="data-font">Disconnected</ng-template>

在Angular 4.0中，if..else语法非常类似于Java中的条件操作符。

在Java中，你使用“条件?stmnt1:stmnt2”。

在Angular 4.0中，你使用*ngIf="condition;then stmnt1 else stmnt2"。

所以，这实际上并没有使用ng-if，但许多建议似乎是处理在条件语句中编写文本。我认为这种方法是用最少的代码或复杂性来做到这一点的最好方法。你来评判吧。

<div>{{variable == null ? 'Testing1' : 'Testing2'}}<div>
OR
<div>{{variable == null ? var1 : var2 }}<div>

ng-template

<ng-template [ngIf]="condition1" [ngIfElse]="template2">
        ...
</ng-template>


<ng-template #template2> 
        ...
</ng-template>

<div *ngIf="show; else elseBlock">Text to show</div>
<ng-template #elseBlock>Alternate text while primary text is hidden</ng-template>