Sometimes, if the component isn’t yet initialized when you access it, you get an error that says that the child component is undefined. … However, even if you access to the child component in the AfterViewInit, sometimes the @ViewChild was still returning null. The problem can be caused by the *ngIf or other directive.
Besides, What is the difference between ViewChild and ViewChildren?
Another critical difference is that @ViewChild returns a single native DOM element as a reference, while the @ViewChildren decorator returns the list of different native DOM elements in the form of QueryList , which contains the set of elements.
Keeping this in mind, What does ViewChild return? The ViewChild or ViewChildren decorators are used to Query and get the reference of the DOM element in the Component. ViewChild returns the first matching element and ViewChildren returns all the matching elements as a QueryList of items. We can use these references to manipulate element properties in the component.
How do you resolve ExpressionChangedAfterItHasBeenCheckedError?
A good way to fix the ExpressionChangedAfterItHasBeenCheckedError is to make Angular aware of the fact that you have changed the code after it has completed its first check. You can do this by using setTimeout to make the error go away.
How do I use ngAfterViewInit?
ngAfterViewInit can be used with @ViewChild() and @ViewChildren() properties. ngAfterContentInit() can be used with @ContentChild and @ContentChildren properties. Angular has one more lifecycle hook i.e. ngOnChanges() which responds when Angular sets or resets data-bound @Input() properties.
What is the difference between ViewChild () and ContentChild ()?
ViewChild is used to select an element from component’s template while ContentChild is used to select projected content.
What is ViewChild and ViewChildren in Angular?
The @ViewChild and @ViewChildren decorators in Angular provide access to child elements in the view DOM by setting up view queries. A view query is a requested reference to a child element within a component view which contains metadata of the element.
What is ViewChild for?
The @ViewChild decorator allows us to inject into a component class references to elements used inside its template, that’s what we should use it for. Using @ViewChild we can easily inject components, directives or plain DOM elements.
What is read in ViewChild?
With {read: SomeType} you tell what type should be returned from the element with the #myname template variable. If you don’t provide the read parameter, @ViewChild() returns the. ElementRef instance if there is no component applied, or the. component instance if there is.
What is ViewChild static true?
The static option for @ViewChild() and @ContentChild() queries determines when the query results become available. With static queries (static: true), the query resolves once the view has been created, but before change detection runs.
What is Changedetectorref?
A change-detection tree collects all views that are to be checked for changes. Use the methods to add and remove views from the tree, initiate change-detection, and explicitly mark views as dirty, meaning that they have changed and need to be re-rendered.
What is difference between ngAfterContentInit and ngAfterViewInit?
ngAfterContentInit : This is called after components external content has been initialized. ngAfterViewInit : This is called after the component view and its child views has been initialized.
What is ngAfterViewChecked?
ngAfterViewChecked()link
A callback method that is invoked immediately after the default change detector has completed one change-check cycle for a component’s view.
How do you use ngDoCheck?
When should you use ngDoCheck? Use ngDoCheck when you want to capture changes that Angular otherwise doesn’t. For example, if a binding references remains unchanged after a click event, ngOnChanges won’t run but ngDoCheck will.
How do you use ngOnChanges?
When should you use ngOnChanges? Use ngOnChanges whenever you want to detect changes from a variable decorated by @Input. Remember that only changes from the parent component will trigger this function. Also remember that changes from the parent still update the child value even without implementing ngOnChanges.
What is ContentChild?
ContentChildren is a parameter decorator that is used to fetch the QueryList of elements or directives from the content DOM. The QueryList is updated whenever the child element/component is added or removed.
What is ContentChild and ContentChildren?
The ContentChild & ContentChildren are decorators, which we use to Query and get the reference to the Projected Content in the DOM. Projected content is the content that this component receives from a parent component. The ContentChild & ContentChildren is very similar to the ViewChild & ViewChildren.
Why do we need ViewChild and ViewChildren in Angular?
ViewChild and ViewChildren can be used to access the properties and methods of the child component. … We will look into the code to access the child component’s properties and methods from the parent component using @ViewChild .
What are decorators in Angular?
Decorators are a design pattern that is used to separate modification or decoration of a class without modifying the original source code. In AngularJS, decorators are functions that allow a service, directive or filter to be modified prior to its usage.
Why do we need template reference variables?
Template variables help you use data from one part of a template in another part of the template. Use template variables to perform tasks such as respond to user input or finely tune your application’s forms. A template variable can refer to the following: a DOM element within a template.
How does ViewChild work in angular?
ViewChildlink
Property decorator that configures a view query. The change detector looks for the first element or the directive matching the selector in the view DOM. If the view DOM changes, and a new child matches the selector, the property is updated.
What is the use of renderer in angular?
The Renderer class is a built-in service that provides an abstraction for UI rendering manipulations. For example, you need to set the focus on an input element, so you may be tempted to do something like: This works fine.
What is use of @ViewChild?
The @ViewChild decorator allows us to inject into a component class references to elements used inside its template, that’s what we should use it for. Using @ViewChild we can easily inject components, directives or plain DOM elements.
What is view in Angular?
Views are almost like their own virtual DOM. Each view contains a reference to a corresponding section of the DOM. Inside a view are nodes that mirror what is in the this section. Angular assigns one view node per DOM element. Each node holds a reference to a matching element.