angular - cdk-virtual-scroll-viewport with variable item heights

Angular - cdk-virtual-scroll-viewport with variable item heights

Using cdk-virtual-scroll-viewport in Angular with variable item heights requires careful handling to ensure correct rendering and scrolling behavior. Here's how you can implement it:

Steps to Use cdk-virtual-scroll-viewport with Variable Item Heights

  1. Install Angular CDK: If you haven't already installed Angular CDK, do so using npm:

    npm install @angular/cdk

  2. Import CDK Virtual Scrolling Module: Import ScrollingModule in your Angular module where you want to use virtual scrolling:

    // app.module.ts or your specific module import { ScrollingModule } from '@angular/cdk/scrolling'; @NgModule({ declarations: [ // Your components ], imports: [ BrowserModule, ScrollingModule, // Other modules ], providers: [], bootstrap: [AppComponent] }) export class AppModule { }

  3. Prepare Data Source: Create a data source that implements CdkVirtualScrollViewportDataSource interface. This source should provide your data and item sizes.

    import { CdkVirtualScrollViewportDataSource } from '@angular/cdk/scrolling'; import { BehaviorSubject } from 'rxjs'; export class MyDataSource extends CdkVirtualScrollViewportDataSource<any> { private data = new BehaviorSubject<any[]>([]); constructor() { super(); } connect() { return this.data.asObservable(); } disconnect() {} setData(data: any[]) { this.data.next(data); } getItemSize(item: any) { // Return the height of each item dynamically based on your logic // For example, you could calculate based on the content or use predefined heights return item.height; // Assuming each item has a 'height' property } }

  4. Use cdk-virtual-scroll-viewport in your Component: Implement virtual scrolling in your component's template:

    <!-- your-component.component.html --> <cdk-virtual-scroll-viewport itemSizeProvider="getItemSize"> <div *cdkVirtualFor="let item of dataSource.connect()"> <!-- Your item template --> <div [style.height.px]="item.height"> <!-- Example: Setting height dynamically --> {{ item.name }} </div> </div> </cdk-virtual-scroll-viewport>

  5. Set Up Component Logic: In your component TypeScript file, initialize and set data to your MyDataSource instance:

    import { Component, OnInit } from '@angular/core'; @Component({ selector: 'app-your-component', templateUrl: './your-component.component.html', styleUrls: ['./your-component.component.css'] }) export class YourComponent implements OnInit { dataSource: MyDataSource; constructor() { this.dataSource = new MyDataSource(); } ngOnInit(): void { // Example: Set data dynamically const data = [ { name: 'Item 1', height: 50 }, { name: 'Item 2', height: 100 }, // More items ]; this.dataSource.setData(data); } }

Explanation:

  • Virtual Scrolling Setup: cdk-virtual-scroll-viewport optimizes rendering by dynamically loading and unloading elements as the user scrolls.
  • Variable Item Heights: Implement getItemSize method in your data source to return the height of each item dynamically.
  • Dynamic Item Rendering: Use *cdkVirtualFor directive to iterate through your data source and render items based on their height dynamically.

By following these steps, you can effectively use cdk-virtual-scroll-viewport in Angular with variable item heights, ensuring efficient rendering and scrolling performance, especially useful when dealing with large lists or items of varying sizes. Adjust the getItemSize method to fit your specific logic for determining item heights based on your application's requirements.

Examples

  1. Setting Up cdk-virtual-scroll-viewport in Angular

    Description: Implementing cdk-virtual-scroll-viewport in an Angular component with variable item heights.

    // app.component.html <cdk-virtual-scroll-viewport itemSize="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items" class="example-item"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items constructor() {} calculateItemSize() { // Logic to calculate item size dynamically based on content or other factors return 50; // Example: Return calculated item height in pixels } }

  2. Handling Variable Item Heights in cdk-virtual-scroll-viewport

    Description: Dynamically calculating and handling variable item heights in cdk-virtual-scroll-viewport.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items" class="example-item"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items constructor() {} calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].length * 20; // Example: Return calculated height based on item content } }

  3. Updating cdk-virtual-scroll-viewport on Item Height Change

    Description: Updating the cdk-virtual-scroll-viewport when item heights change dynamically.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component, ViewChild } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport; constructor() {} calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].length * 20; // Example: Return calculated height based on item content } trackByFn(index: number, item: any) { return index; // Ensure each item has a unique identifier } updateViewport() { this.viewport.checkViewportSize(); } }

  4. Lazy Loading Images in cdk-virtual-scroll-viewport

    Description: Implementing lazy loading of images within cdk-virtual-scroll-viewport with variable item heights.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item"> <img [src]="item.imageUrl" [style.height.px]="calculateItemSize()"> <p>{{ item.description }}</p> </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component, ViewChild } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; interface Item { imageUrl: string; description: string; } @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items: Item[] = [...]; // Your items with image URLs and descriptions @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport; constructor() {} calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].description.length * 20 + 100; // Example: Adjust height based on content and image height } trackByFn(index: number, item: any) { return item.imageUrl; // Track items by image URL for efficiency } updateViewport() { this.viewport.checkViewportSize(); } }

  5. Handling Item Height Changes and Refreshing cdk-virtual-scroll-viewport

    Description: Handling dynamic changes in item heights and refreshing cdk-virtual-scroll-viewport.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component, ViewChild } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport; constructor() {} calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].length * 20; // Example: Return calculated height based on item content } trackByFn(index: number, item: any) { return index; // Ensure each item has a unique identifier } updateViewport() { this.viewport.checkViewportSize(); } onItemHeightChange() { // Trigger this method when item heights change dynamically this.updateViewport(); // Refresh viewport to reflect changes } }

  6. Custom Styling for cdk-virtual-scroll-viewport with Variable Heights

    Description: Applying custom styles to cdk-virtual-scroll-viewport items when using variable item heights.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item" [style.height.px]="calculateItemSize()"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.css .example-item { border: 1px solid #ccc; padding: 10px; margin-bottom: 5px; background-color: #f0f0f0; }

  7. Handling Dynamic Content Changes in cdk-virtual-scroll-viewport

    Description: Managing dynamic content changes within cdk-virtual-scroll-viewport with variable item heights.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item" [style.height.px]="calculateItemSize()"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component, ViewChild, ChangeDetectorRef } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport; constructor(private cdr: ChangeDetectorRef) {} ngAfterViewInit() { this.cdr.detectChanges(); // Detect changes after view initialization } calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].length * 20; // Example: Return calculated height based on item content } trackByFn(index: number, item: any) { return index; // Ensure each item has a unique identifier } }

  8. Handling Large Data Sets in cdk-virtual-scroll-viewport

    Description: Optimizing performance with large data sets in cdk-virtual-scroll-viewport and variable item heights.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component, ViewChild } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport; constructor() {} calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].length * 20; // Example: Return calculated height based on item content } trackByFn(index: number, item: any) { return index; // Ensure each item has a unique identifier } }

  9. Lazy Loading Data in cdk-virtual-scroll-viewport

    Description: Implementing lazy loading of data within cdk-virtual-scroll-viewport with variable item heights.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component, ViewChild } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport; constructor() {} calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].length * 20; // Example: Return calculated height based on item content } trackByFn(index: number, item: any) { return index; // Ensure each item has a unique identifier } }

  10. Implementing Infinite Scroll with cdk-virtual-scroll-viewport

    Description: Implementing infinite scroll functionality using cdk-virtual-scroll-viewport with variable item heights.

    // app.component.html <cdk-virtual-scroll-viewport [itemSize]="calculateItemSize()" class="example-viewport" (scrolledIndexChange)="loadMoreItems($event)"> <div *cdkVirtualFor="let item of items; trackBy: trackByFn" class="example-item"> {{ item }} </div> </cdk-virtual-scroll-viewport> // app.component.ts import { Component, ViewChild } from '@angular/core'; import { CdkVirtualScrollViewport } from '@angular/cdk/scrolling'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { items = ['Item 1', 'Item 2', 'Item 3', ...]; // Your variable-height items @ViewChild(CdkVirtualScrollViewport) viewport: CdkVirtualScrollViewport; constructor() {} calculateItemSize(index: number) { // Logic to calculate item size dynamically based on content or other factors return this.items[index].length * 20; // Example: Return calculated height based on item content } trackByFn(index: number, item: any) { return index; // Ensure each item has a unique identifier } loadMoreItems(index: number) { // Implement logic to load more items as the user scrolls // Example: this.items.push(...newItems); } }

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