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Angular Material Drag And Drop UI Component(Part-2)


Part -1 Precap:

Introduction to drag and drop Angular Material CDK.
Discussed cdkDrag Directive
Discussed cdkDropList Directive
Discussed the cdkDropListDropped event.

cdkDropListConnectedTo Directive:

cdkDropListConnectedTo directive helps to drag and drop of items between the multiple cdkDropList instances. The communication between two different cdkDropList established either by assigning the cdkDropList template variable to the cdkDropListConnectedTo directive or by assigning the cdkDropList Html element id value to cdkDropListConnectedTo directive.

cdkDropListData Directive:

cdkDropListData Directive takes input like a component object that will render as Html Element items in cdkDropList instance. By assigning a component model object to cdkDropListData, makes our data to available in CDK drag and drop instance for sorting the data on each drag and drop of elements.

transferArrayItem method:

  • transferArrayItem method gets loaded from '@angular/cdk/drag-drop'. This method uses the component model data that was assigned to the cdkDropListData directive and then sort that data.
  • By using the cdkDropListConnectedTo directive will transfer data from one cdkDropList instance to another cdkDropList instance which means moving an item from one model object to another model object. 
  • By using the transferArrayItem method we can sort the data of both source and destination cdkDroList instances model objects.

Sample Using cdkDropListConnectedTo Directive:

Let's implement a sample example of drag and drop of data from one instance to another instance using the cdkDropListConnectedTo directive.

Let's add the CSS for our sample as below.
src/app/groupDragDrop/group.drag.drop.component.css:
.my-container {
    width: 400px;
    max-width: 100%;
    margin: 0 25px 25px 0;
    display: inline-block;
    vertical-align: top;
  }
  
  .my-list {
    border: solid 1px #ccc;
    min-height: 60px;
    background: white;
    border-radius: 4px;
    overflow: hidden;
    display: block;
  }
  
  .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);
  }
Now let's add model objects in the component class follows
src/app/groupDragDrop/group.drag.drop.component.ts:
import {Component} from '@angular/core';
import { moveItemInArray, transferArrayItem, CdkDragDrop } from '@angular/cdk/drag-drop';

@Component({
    selector:'group-drag-drop',
    templateUrl:'group.drag.drop.component.html',
    styleUrls:['group.drag.drop.component.css']
})
export class GroupDragDropComponent {
    squad = [
        "Rohit Sharma",
        "Virat Kohli",
        "Ms Dhoni",
        "Shikar Dhawan",
        "Ambati Rayudu",
        "Suresh Raina"
    ];

    selectedPlayers =[];

    drop(event:CdkDragDrop<string[]>){
        console.log(event);
    }
}
  • #L2 at this line loading CdkDragDrop, moveItemArray, tranferArrayItem from '@angular/cdk/drag-drop' package.
  • #L10-L17 at these lines initialized array of strings, this array object will be assigned to the cdkDropListData directive of one of the instances of cdkDropList.
  • #L19 at this initialized empty array object, this object will be assigned to the cdkDropListData directive of another cdkDrpList. Here the main idea is we going to drag and drop data from either 'squad' object to 'selectedPlayers' object or 'selectedPlayers' object to 'squad' object.
  • #L21-L23 at these line component method 'drop' created this method will be registered with cdkDropListDropped event. Currently, no logic is implemented inside of this method, in upcoming steps we will update this method logic.
Now let's add Html code as follows.
src/app/groupDragDrop/group.drag.drop.component.html:
<div class="my-container">
   <h2>Full Squad</h2>

   <div
    cdkDropList
    #fullSquadList = "cdkDropList"
    [cdkDropListData]="squad"
    [cdkDropListConnectedTo]="[selectedTeamList]"
    class="my-list"
    (cdkDropListDropped)="drop($event)">
    <div class="my-box" *ngFor="let player of squad" cdkDrag>{{player}}</div>
   </div>
</div>

<div class="my-container">
    <h2>Selected Team</h2>
    <div
     cdkDropList
     #selectedTeamList="cdkDropList"
     [cdkDropListData]="selectedPlayers"
     [cdkDropListConnectedTo]="[fullSquadList]"
     class="my-list"
     (cdkDropListDropped)="drop($event)">
      <div class="my-box" *ngFor="let player of selectedPlayers" cdkDrag>
         {{player}}
      </div>
    </div>
</div>
  • Here we can observe 2 separate containers of div elements declared.
  • #L5&L18 at these lines div element of each container decorated with cdkDropList directive.
  • #L10&L23 at these lines div element configured with cdkDropListDropped event and to this event, we configured 'drop' method.
  • #L6 at this line '#fullSquadList' is a template variable that will represent one of the containers. This template variable will be used as input value to 'cdkDropListConnectedTo' directive of another container to establish communication between containers.
  • #L19 at this line '#selectedTeamList' is a template variable that will represent one of the containers. This template variable will be used as the input value to 'cdkDropListConnectedTo' directive of another container to establish communication between the container.
  • #L7 at this line cdkDropListData directive declared this will take input data from the component object. Here we assign 'squad'(array of strings object). By assigning data to cdkDropListData will help us to fetch the data object at the cdkDropListDropped event.
  • #L20 at this line cdkDropListData directive declares and it takes input as 'selectedPlayers'(empty array object to which data get populated on drag and drop the element from the first container).
  • #L8&L21 at these lines cdkDropListConnectedTo directive declared, which takes input as angular template variables of other containers to make communication between those containers.
  • #L11&L24 at these lines cdkDrag directive added to div element to make the draggable elements.
Now let's add component Html tag on the app component Html file as below.
src/app/app.component.html:
<group-drag-drop></group-drag-drop>
Now let's import our component on to app module file as below.
src/app/app.module.ts:
import { GroupDragDropComponent } from './groupDragDrop/group.drag.drop.component';

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

Now if we try to drag and drop items from container1 to container2 will not work it will get refershed to initial state. If we try to drag and drop items by sorting items with in the containers also will not work

The reason for this is we haven't sorted the data objects like 'squad', 'selectedPlayers' in our component. This sorting of data will be implemented in 'drop' method in our component in upcoming steps.
Let's start fixing the sorting of items in its own container.
src/app/groupDragDrop/group.drag.drop.component.ts:
drop(event:CdkDragDrop<string[]>){
	console.log(event);
	if(event.previousContainer === event.container){
		 moveItemInArray(event.container.data, event.previousIndex, event.currentIndex)
	}
}
  • #L3 at this line we can observe 'previousContainer', 'container' props from CdkDragDrop instance. 
  • Each cdkDropList instance represents a container. 
  • So on dragging and dropping of an element in cdkDropList instance, the cdkDropListDropped event gets invoked in which each container information will be automatically populated as event information of drag and drop. 
  • Since we want to fix the issue of sorting or drag and drop of the element within the container(cdkDropList instance). 
  • So here we check for 'previousContainer' matches with the container(element dropped current container). If matches drag and drop implemented inside of the container. Then using 'moveItemArray' we will sort the component data object. 
  • If you carefully observe we are not accessing the component object directly but we are using 'event.container.data'. If you recall we assigned cdkDropListData directive in HTML assigned with component data, the same data will be passed to container and can be accessed as 'event.container.data'.
  • Finally, using component data and previous index and current index data will be sorted as per drag and drop of an element.
Now run the application and outputs shows as below.
Now within the container 1 drag, the 1st element to 3rd position and the output shows as below.
Now we need to fix the issue drag and drop of items between the containers.
src/app/groupDragDrop/group.drag.drop.component.ts:
drop(event:CdkDragDrop<string[]>){
	console.log(event);
	if(event.previousContainer === event.container){
		moveItemInArray(event.container.data, event.previousIndex, event.currentIndex)
	}else{
		transferArrayItem(
			event.previousContainer.data,
			event.container.data,
			event.previousIndex,
			event.currentIndex
		);
	}
}
#L6-L11 at these lines 'transferArrayItem' method used to sort the data drag and dropped between two or more containers(cdkDropList instances). It takes 'event.previousContainer.data'(represents source container data from where the element will be dragged), 'event.container.data'(represents the destination container data from where the element will be dropped).

Now run the application and output shows as below.
After dragging and dropping a few items on container2 and then output shows as below.

cdkDropListGroup Directive:

cdkDropListGroup directive is another way of grouping the cdkDropList instances. This approach is the best technique for grouping the N-number of cdkDropList instances dynamically.

Example Using cdkDropListGroup Directive:

src/app/groupDragDrop/dynamic.group.component.ts:
import { Component } from '@angular/core';
import {CdkDragDrop, moveItemInArray, transferArrayItem, DragDrop} from '@angular/cdk/drag-drop';

@Component({
    selector:'dynamic-group',
    templateUrl:'dynamic.group.component.html',
    styleUrls:['dynamic.group.component.css']
})
export class DynamicGroupComponent {
    data = [{
        Catergory:"Fruits",
        Items:[
            "Mango",
            "Apple",
            "Banana",
            "WaterMelon",
            "Sapota",
        ]
    },{
        Catergory:"Juice",
        Items:[
            "Mango Juice",
            "Apple Juice",
            "Banana Juice",
            "WaterMelon Juice",
            "Sapota Juice",
        ]
    }];
    drop(events:CdkDragDrop<string[]>){
        if(events.previousContainer === events.container){
            moveItemInArray(events.container.data, events.previousIndex, events.currentIndex);
        }else{
            transferArrayItem(events.previousContainer.data, events.container.data, events.previousIndex,events.currentIndex);
        }
    }
}
#L10-L28 at these lines collection objects assigned to the 'data' variable. Each object in the collection represents a cdkDropList instance and these instances are grouped by cdkDropListGroup directive.

Styling for this new component the same as the above example we discussed so copy those styles to this component CSS file.

Now let's add HTML wit cdkDropListGroup directive which contains dynamically created cdkDropList instances as below
src/app/groupDragDrop/dynamic.group.component.html:
<div cdkDropListGroup>
    <div class="my-container" *ngFor="let d of data">
        <h2>{{d.Catergory}}</h2>
     
        <div
         cdkDropList
         [cdkDropListData]="d.Items"
         class="my-list"
         (cdkDropListDropped)="drop($event)">
         <div class="my-box" *ngFor="let item of d.Items" cdkDrag>{{item}}</div>
        </div>
     </div>
</div>
  • #L1 at this line cdkDropListGroup directive decorated to group the cdkDropList instances dynamically.
  • #L2 at this line by looping 'data' object cdkDropList instances created dynamically.
Now add the new component Html tag on to the app component HTML as below
src/app/app.component.html:
<dynamic-group></dynamic-group>
Now import the new component on to the app module file as below.
src/app/app.module.ts:
import { DynamicGroupComponent } from './groupDragDrop/dynamic.group.component';

@NgModule({
  declarations: [
    DynamicGroupComponent
  ],
})
export class AppModule {}
// code hidden for display purpose
Now run the application and output shows as below.
After swapping items by drag and drop then 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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