Android Drag and Drop: Enhancing User Interaction

In this article, you will learn about implementing Android drag and drop. You will also discover the benefits of using this feature and best practices to ensure an optimal user experience.

Android Drag and Drop Framework supports drag-and-drop in many applications. It allows you to create intuitive and engaging user interfaces by allowing users to drag and drop items within or between apps. It is a widely used feature in both mobile and web applications.

The drag and drop functionality in Android is based on the following classes:

Android Drag And Drop Process

Android drag and drop involves the following steps:

1. The user initiates the drag operation by pressing and holding a view. During this event, the startDrag() method is invoked, which creates a DragShadowBuilder object that shows the dragged view visually.
2. When the user moves the view, the system generates ACTION_DRAG_ENTERED events, indicating that the drag has entered a new area. The target area where the view can be dropped is typically highlighted by this event.
3. In response to the user moving the view, the system generates ACTION_DRAG_LOCATION events, indicating the current position. In this event, the visual representation of the dragged view can be updated.
4. The system generates an ACTION_DRAG_EXITED event when the user moves the view out of the target area.
5. ACTION_DROP events are generated when the user releases the view over the target area, indicating that the view has been dropped. Using this event, you can update the application state based on the drop.
6. When the drag operation has ended, the system generates an ACTION_DRAG_ENDED event. Using this event, any drag-associated resources can be cleaned up.

The DragEvent Class

In Android, DragEvent represents an event that occurs during drag-and-drop operations.

Information about a drag-and-drop operation is provided, including information about the action, the drag event position, and the data that is being dragged.

Constants

Here are the constants present in the DragEvent class:

DragEvent Methods

Methods of the DragEvent class are examined below:

Listening Drag Events

We need to implement the OnDragListener interface in an Android app to listen for drag events.

Android provides the OnDragListener interface for detecting drag events on views.

OnDragListener listens for drag and drop events and is associated with the view receiving the data.

This interface provides two methods to implement:

A brief example of using OnDragListener to implement drag-and-drop functionality in Android is shown below.

First, let’s create two views: one view that we want to drag and another one that will serve as our drop target.

For this example, we will be using two TextView objects. To make it easy to differentiate between the two views, we will add a background drawable to each of them.

<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<TextView
android:id="@+id/draggable_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Drag me"
android:padding="16dp"
android:background="@drawable/draggable_background" />

<TextView
android:id="@+id/drop_target"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Drop here"
android:padding="16dp"
android:background="@drawable/drop_target_background" />

</LinearLayout>

After creating the two views, we will implement the OnDragListener interface for the drop target view.

By doing so, we can handle the actual drop event in the onDrag() method.

To handle specific drag events, we can add code to the appropriate case block.

TextView draggableText = findViewById(R.id.draggable_text);
TextView dropTarget = findViewById(R.id.drop_target);

dropTarget.setOnDragListener(new View.OnDragListener() {
@Override
public boolean onDrag(View v, DragEvent event) {
switch (event.getAction()) {
case DragEvent.ACTION_DRAG_STARTED:
// Code to handle drag started event
return true;

case DragEvent.ACTION_DRAG_ENTERED:
// Code to handle drag entered event
return true;

case DragEvent.ACTION_DRAG_LOCATION:
// Code to handle drag location event
return true;

case DragEvent.ACTION_DRAG_EXITED:
// Code to handle drag exited event
return true;

case DragEvent.ACTION_DROP:
// Code to handle drop event
return true;

case DragEvent.ACTION_DRAG_ENDED:
// Code to handle drag ended event
return true;

default:
return false;
}
}
});

Now, we can make the draggable view actually draggable by implementing a View.OnLongClickListener for the draggable view.

Inside the onLongClick() method, we’ll start the drag operation by creating a View.DragShadowBuilder object to provide a visual representation of the dragged view and calling startDragAndDrop(). This method takes a ClipData object and a View.DragShadowBuilder object as parameters. The ClipData object holds the data to be dragged and the View.DragShadowBuilder object provides a visual representation of the dragged view during the drag operation.

draggableText.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(v);
v.startDragAndDrop(null, shadowBuilder, null, 0);
return true;
}
});

Android Drag and Drop Best Practices

To ensure that the drag and drop functionality in your app is optimal, it is important to follow these best practices:

• Provide visual feedback to the user during the drag and drop operation, such as a visual cue to indicate the drop target.
• Ensure that the drag and drop feature is accessible to users with disabilities by providing alternative ways to interact with the UI.
• Optimize the drag and drop feature for performance by minimizing unnecessary redraws and animations.
• Maintain consistency in the drag and drop behavior across all views and ensure that the user can easily understand how to use the feature.

Advantages

Some of the advantages of drag and drop in Android are:

In this article, you learned how to implement drag and drop functionality in your Android app. You discovered the three main classes used in drag and drop: DragShadowBuilder, DragEvent, and OnDragListener. Additionally, we went through the steps involved in implementing drag and drop in an Android application.