ngif else if with code examples

The ngif directive in Angular allows you to conditionally render a section of your template based on a boolean expression. You can use this directive to show or hide elements, or even entire components, based on the value of a variable or expression.

The basic syntax for using ngif is as follows:

<element *ngIf="expression"></element>

In this example, the expression is a boolean value that determines whether the element is rendered or not. If the expression is true, the element is rendered, otherwise it is not.

You can also use the else clause to specify what should be rendered if the expression is false:

<element *ngIf="expression; else elseBlock"></element>
<ng-template #elseBlock>
  <p>The element is not rendered</p>
</ng-template>

In the above example, if the expression is false, the text "The element is not rendered" will be displayed instead of the element.

You can also use multiple else if clause to create more complex conditions. For example, you can use the following code to display different messages based on the value of a variable:

<div *ngIf="variable === 1; else elseBlock1">
  <p>The variable is 1</p>
</div>
<ng-template #elseBlock1>
  <ng-container *ngIf="variable === 2; else elseBlock2">
    <p>The variable is 2</p>
  </ng-container>
  <ng-template #elseBlock2>
    <p>The variable is not 1 or 2</p>
  </ng-template>
</ng-template>

In this example, if the value of variable is 1, the text "The variable is 1" will be displayed. If the value of variable is 2, the text "The variable is 2" will be displayed. Otherwise, the text "The variable is not 1 or 2" will be displayed.

It is important to note that using ngif directive with else or else if can cause change detection cycle and decrease the performance of your application. It is recommended to use ngif with else or else if only when it is strictly necessary.

In summary, the ngif directive in Angular allows you to conditionally render a section of your template based on a boolean expression. You can use the else and else if clauses to create more complex conditions and control the flow of your application.

One topic related to the ngif directive is the ngswitch directive. This directive allows you to conditionally render elements based on the value of an expression. The basic syntax for using ngswitch is as follows:

<element [ngSwitch]="expression">
  <p *ngSwitchCase="value1">Value is 1</p>
  <p *ngSwitchCase="value2">Value is 2</p>
  <p *ngSwitchDefault>Value is not 1 or 2</p>
</element>

In this example, the expression is evaluated and its value is compared to the values specified in the ngSwitchCase directives. If the value of the expression matches one of the values, the corresponding element will be rendered. If the value of the expression does not match any of the values, the element with the ngSwitchDefault directive will be rendered.

ngswitch and ngif can be used together in some cases. For example, you can use ngif to check if a variable exists before using ngswitch to determine its value.

<div *ngIf="variable">
  <div [ngSwitch]="variable.value">
    <p *ngSwitchCase="1">Variable is 1</p>
    <p *ngSwitchCase="2">Variable is 2</p>
    <p *ngSwitchDefault>Variable is not 1 or 2</p>
  </div>
</div>

Another topic related to the ngif directive is the ngfor directive. This directive is used to iterate over an array or an iterable object and render a template for each item. The basic syntax for using ngfor is as follows:

<element *ngFor="let item of items">
  {{ item }}
</element>

In this example, the items is an array or an iterable object, and the item is a variable that will take the value of each item in the array or object. The element will be rendered for each item in the array or object, and the value of the item variable will be displayed inside the element.

You can also use the index variable in the ngFor directive to access the current index of the item.

<element *ngFor="let item of items; index as i">
  {{ i }}: {{ item }}
</element>

In this example, the i variable will take the value of the current index of the item.

In summary, the ngswitch directive allows you to conditionally render elements based on the value of an expression, while the ngfor directive allows you to iterate over an array or an iterable object and render a template for each item. Both ngif and ngfor can be used together in some cases to achieve more complex logic.

Popular questions

1. What is the basic syntax for using the ngif directive in Angular?

• The basic syntax for using ngif is as follows: <element *ngIf="expression"></element>

2. How can you specify what should be rendered if the expression in an ngif directive is false?

• You can use the else clause to specify what should be rendered if the expression is false. The syntax is: <element *ngIf="expression; else elseBlock"></element> <ng-template #elseBlock> <p>The element is not rendered</p> </ng-template>

3. How can you use multiple else if clauses to create more complex conditions with the ngif directive?

• You can use multiple ng-container with ngif to create more complex conditions. For example, you can use the following code to display different messages based on the value of a variable:

<div *ngIf="variable === 1; else elseBlock1">
  <p>The variable is 1</p>
</div>
<ng-template #elseBlock1>
  <ng-container *ngIf="variable === 2; else elseBlock2">
    <p>The variable is 2</p>
  </ng-container>
  <ng-template #elseBlock2>
    <p>The variable is not 1 or 2</p>
  </ng-template>
</ng-template>

4. How does the ngswitch directive differ from the ngif directive?

• The ngswitch directive allows you to conditionally render elements based on the value of an expression, while the ngif directive allows you to conditionally render a section of your template based on a boolean expression.

5. Can you use the ngfor directive together with the ngif directive?

• Yes, you can use ngif and ngfor together in some cases to achieve more complex logic. For example, you can use ngif to check if a variable exists before using ngfor to iterate over its value.

<div *ngIf="variable">
  <div *ngFor="let item of variable.items">
    {{ item }}
  </div>
</div>

It is important to note that using ngif and ngfor together can cause change detection cycle and decrease the performance of your application. It is recommended to use them together only when it is strictly necessary.

Tag

Conditional.