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Angular Material Drag And Drop UI Component(Part-1)


Angular Material Drag And Drop CDK provides a set of rich functionalities like as below:
  • Able to apply to drag functionality on any HTML elements with free motion over a page
  • Sorting list of HTML rendered items.
  • Custom drag handlers
  • Custom drag place holders
  • Limit the area to drag for an item.
This article is a series of parts where we going to discuss and understand all the features provided by drag and drop CDK.

Create An Angular Sample Application:

To understand step by step implementation of drag and drop functionalities, let's create a sample angular application.
Command to create angular application:

ng new your-project-name
Command to install angular material package:

ng add @angular/material

Import DragDropModule:

DragDropModule is loaded from '@angular/cdk/drag-drop' package. Now we need to import this DragDropModule on to the NgModule of the app module to get all features of it.
src/app/app.module.ts:
import { DragDropModule } from '@angular/cdk/drag-drop';

@NgModule({
  imports: [DragDropModule]
})
export class AppModule {}
// code hidden due to display purpose

cdkDrag Directive:

Adding cdkDrag Directive on an HTML element will get the ability to drag and drop.

Simple Example On Drag And Drop With cdkDrag Directive:

Let's create a simple example on drag and drop with cdkDrag directive as follows.
src/app/cdkDragSample/cdk.drag.sample.component.ts:
import { Component } from '@angular/core';

@Component({
    selector:'cdk-drag-sample',
    templateUrl:'cdk.drag.sample.component.html',
    styleUrls:['cdk.drag.sample.component.css']
})
export class CdkDragSampleComponent {

}
Now add the following CSS styles to the component styles file
src/app/cdkDragSample/cdk.drag.sample.component.css:
.my-box {
    width: 200px;
    height: 200px;
    border: solid 1px #ccc;
    color: rgba(0, 0, 0, 0.87);
    cursor: move;
    display: flex;
    justify-content: center;
    align-items: center;
    text-align: center;
    background: #fff;
    border-radius: 4px;
    position: relative;
    z-index: 1;
    transition: box-shadow 200ms cubic-bezier(0, 0, 0.2, 1);
    box-shadow: 0 3px 1px -2px rgba(0, 0, 0, 0.2),
                0 2px 2px 0 rgba(0, 0, 0, 0.14),
                0 1px 5px 0 rgba(0, 0, 0, 0.12);
  }
  
  .my-box:active {
    box-shadow: 0 5px 5px -3px rgba(0, 0, 0, 0.2),
                0 8px 10px 1px rgba(0, 0, 0, 0.14),
                0 3px 14px 2px rgba(0, 0, 0, 0.12);
  }
Now let add HTML element with cdkDrag directive on it.
src/app/cdkDragSample/cdk.drag.sample.component.html:
<div class="my-box" cdkDrag>
    Hey you can drag me!
    Because i use cdKDrag directive
</div>
#L1 at this line cdkDrag directive decorated on 'div' element. Now this 'div' element has the capability of drag and drops on any place on a page.

Now let's run the application and output shows as below.

cdkDropList Directive:

cdkDropList directive applied over the group of Html elements each is decorated with cdkDrag directive. By using the cdkDropList directive we can do list elements ordering within its range. So the cdkDropList directive will act as a parent to the group of cdkDrag directives.

Drag And Drop List Of Elements By Using cdkDropList Directive:

Let's start creating a sample application for the Html element list sorting using the cdkDropList Directive.
src/app/listOrder/list.order.component.ts:
import { Component } from '@angular/core';

@Component({
    selector:'list-order',
    templateUrl:'list.order.component.html',
    styleUrls:['list.order.component.css']
})
export class ListOrderComponent {
    players = [
       'Rohit Sharma',
       'Shikar Dhawan',
       'Virat Kohli',
       'Ms Dhoni',
       'Ambati Rayudu',
       'Hardik Pandya'
    ];
}
#L9-L16 at these lines array of data that is going to be rendered as a list.

Let's add the following styles in the component styles file.
src/app/listOrder/list.order.component.css:
.my-list {
    width: 500px;
    max-width: 100%;
    border: solid 1px #ccc;
    min-height: 60px;
    display: block;
    background: white;
    border-radius: 4px;
    overflow: hidden;
  }
  
  .my-box {
    padding: 20px 10px;
    border-bottom: solid 1px #ccc;
    color: rgba(0, 0, 0, 0.87);
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content: space-between;
    box-sizing: border-box;
    cursor: move;
    background: white;
    font-size: 14px;
  }
  
  .cdk-drag-preview {
    box-sizing: border-box;
    border-radius: 4px;
    box-shadow: 0 5px 5px -3px rgba(0, 0, 0, 0.2),
                0 8px 10px 1px rgba(0, 0, 0, 0.14),
                0 3px 14px 2px rgba(0, 0, 0, 0.12);
  }
  
  .cdk-drag-placeholder {
    opacity: 0;
  }
  
  .cdk-drag-animating {
    transition: transform 250ms cubic-bezier(0, 0, 0.2, 1);
  }
  
  .my-box:last-child {
    border: none;
  }
  
  .my-list.cdk-drop-list-dragging .my-box:not(.cdk-drag-placeholder) {
    transition: transform 250ms cubic-bezier(0, 0, 0.2, 1);
  }
Let's add the component Html as follows.
src/app/listOrder/list.order.component.html:
<div class="my-list" cdkDropList>
    <div class="my-box" *ngFor="let player of players" cdkDrag>
        {{player}}
    </div>
</div>
  • #L1 at this line parent div element decorated with cdkDropList directive.
  • #L2 at this line div element decorated with cdkDrag directive makes this element as draggable. Since it, parent element decorated with cdKDropList all the draggable elements inside of it will be sorted within its range. "players" is a component array of data property that will get render by looping the data.
Now, reference this list order component HTML selector on to the app component HTML as below.
src/app/app.component.html:
<list-order></list-order>
Now import the list order component to the app module as below.
import { ListOrderComponent } from './listOrder/list.order.component';

@NgModule({
  declarations: [
    ListOrderComponent,
  ]
})
export class AppModule {}
// code hidden for display purpose
Now run the application and output shows as below.

Above Example Result:

We can observe in above example we are able to drag and drop the element with in the cdkDropList range. But after drag and drop item, we can observe that items refreshed back to original positions, means the result looks same as on pageload. It looks like drog and drop not working. But what happens actually is html element gets drag and dropped successfully, but the data binded(players component property) will not get sorted automatically on using cdkDropList dirctive.

so to fix the result of this example we need to use 'cdkDropListDropped' event.

cdkDropListDropped Event:

cdkDropListDropped event used to update the component data on dragging and dropping of an element.

Let's add a method that will be invoked by the cdkDrpListDropped event as follows.
src/app/listOrder/list.order.component.ts:(update file)
import {CdkDragDrop, moveItemInArray} from '@angular/cdk/drag-drop';
@Component({
    selector:'list-order',
    templateUrl:'list.order.component.html',
    styleUrls:['list.order.component.css']
})
export class ListOrderComponent {
    drop(event:CdkDragDrop<string[]>){
        moveItemInArray(this.players, event.previousIndex, event.currentIndex);
    }
}
// code hidden for display purpose
  • #L1 at this line CdkDragDrop instance and moveItemInArry method are get imported from '@angular/cd/drag-drop' package
  • CdkDragDrop is an instance of the generic type where can capture event data of the cdkDropListDroped event.
  • moveItemInArray is a method, that takes our array of data as input it will sort the data as per drag and drop element indexing.
  • #L8-L10 at these lines 'drop' a component method is created and this method will be registered to listen for the cdkDropListDropped event.
  • #L9 at this line moveItemInArray method gets called by inputting our 'players' property which of type array of objects and then index values to as input values to sort the 'players' property data based on drag and drop position.
Let's register Html with cdkDropListDropped event as below
src/app/listOrder/list.order.component.html:(update file)
<div class="my-list" cdkDropList (cdkDropListDropped)="drop($event)">
    <div class="my-box" *ngFor="let player of players" cdkDrag>
        {{player}}
    </div>
</div>
#L1 at this line 'cdkDropListDropped' event registered with 'drop'(method in component)

Now run the application and output shows as below.
After dragging and dropping output shows as below
Now we observe data get successfully updated on dragging and dropping of an element.

Sample Example Using Data Object Array:

Previously we used data objects as an array of string values, now we going to replace it with an array of object models.

src/app/listOrder/list.order.component.ts:(update file)
import { Component } from '@angular/core';
import {CdkDragDrop, moveItemInArray} from '@angular/cdk/drag-drop';

@Component({
    selector:'list-order',
    templateUrl:'list.order.component.html',
    styleUrls:['list.order.component.css']
})
export class ListOrderComponent {
    players:any[]=[{
        id: 1,
        Name:"Rohit Sharma",
        Position:1 
    },{
        id:2,
        Name:"Virat Kohli",
        Position:2
    },{
        id:3,
        Name:"MS Dhoni",
        Position:3
    },{
        id:4,
        Name:"Shikar Dhawan",
        Position:4
    },{
        id:5,
        Name:"Ambati Rayudu",
        Position:5
    }]

    drop(event:CdkDragDrop<string[]>){
        moveItemInArray(this.players, event.previousIndex, event.currentIndex);
        this.players.forEach((value, index) => {
            value.Position = (index + 1);
        });
    }
}
  • #L10-L30 at these lines array of players object initialized(previously we used an array of string values).
  • #L33 at this line moveItemInArray sorts the object based on drag and drop indexes.
  • #L34-L36 at these lines since moveItemInArray method sorts "players" array object, after that we can update the correct 'Position' value using its index.
Let's update the Html code as follows.
src/app/listOrder/list.order.component.html:(update file)
<div class="my-list" cdkDropList (cdkDropListDropped)="drop($event)">
    <div class="my-box" *ngFor="let player of players" cdkDrag>
        Name: {{player.Name}},   Position:{{player.Position}}
    </div>
</div>
Now run the application and output shows as below.
After drag and drop, the output shows as below.

Wrapping Up:

Hopefully, I think this article delivered some useful information on the Drag and Drop Angular Material CDK. I love to have your feedback, suggestions, and better techniques in the comment section below.

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