DragStartHelper

Kotlin |Java

open class DragStartHelper

kotlin.Any
↳	androidx.core.view.DragStartHelper

DragStartHelper is a utility class for implementing drag and drop support.

It detects gestures commonly used to start drag (long click for any input source, click and drag for mouse).

It also keeps track of the screen location where the drag started, and helps determining the hot spot position for a drag shadow.

Implement DragStartHelper.OnDragStartListener to start the drag operation:

DragStartHelper.OnDragStartListener listener = new DragStartHelper.OnDragStartListener {
      protected void onDragStart(View view, DragStartHelper helper) {
          View.DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view) {
              public void onProvideShadowMetrics(Point shadowSize, Point shadowTouchPoint) {
                  super.onProvideShadowMetrics(shadowSize, shadowTouchPoint);
                  helper.getTouchPosition(shadowTouchPoint);
              }
          };
          view.startDrag(mClipData, shadowBuilder, mLocalState, mDragFlags);
      }
  };
  mDragStartHelper = new DragStartHelper(mDraggableView, listener);

Once created, DragStartHelper can be attached to a view (this will replace existing long click and touch listeners):

mDragStartHelper.attach();

It may also be used in combination with existing listeners:

public boolean onTouch(View view, MotionEvent event) {
      if (mDragStartHelper.onTouch(view, event)) {
          return true;
      }
      return handleTouchEvent(view, event);
  }
  public boolean onLongClick(View view) {
      if (mDragStartHelper.onLongClick(view)) {
          return true;
      }
      return handleLongClickEvent(view);
  }

Summary

Nested classes
abstract	`OnDragStartListener` Interface definition for a callback to be invoked when a drag start gesture is detected.

Public constructors
`<init>(view: View!, listener: DragStartHelper.OnDragStartListener!)` Create a DragStartHelper associated with the specified view.

Public methods
open Unit	`attach()` Attach the helper to the view.
open Unit	`detach()` Detach the helper from the view.
open Unit	`getTouchPosition(point: Point!)` Compute the position of the touch event that started the drag operation.
open Boolean	`onLongClick(v: View!)` Handle a long click event.
open Boolean	`onTouch(v: View!, event: MotionEvent!)` Handle a touch event.

Public constructors

<init>

DragStartHelper(
    view: View!, 
    listener: DragStartHelper.OnDragStartListener!)

Create a DragStartHelper associated with the specified view. The newly created helper is not initially attached to the view, attach must be called explicitly.

Parameters
`view`	View!: A View

Public methods

attach

open fun attach(): Unit

Attach the helper to the view.

This will replace previously existing touch and long click listeners.

detach

open fun detach(): Unit

Detach the helper from the view.

This will reset touch and long click listeners to null.

getTouchPosition

open fun getTouchPosition(point: Point!): Unit

Compute the position of the touch event that started the drag operation.

Parameters
`point`	Point!: The position of the touch event that started the drag operation.

onLongClick

open fun onLongClick(v: View!): Boolean

Handle a long click event.

Parameters
`v`	View!: The view that was clicked and held.

Return
`Boolean`	true if the callback consumed the long click, false otherwise.

onTouch

open fun onTouch(
    v: View!, 
    event: MotionEvent!
): Boolean

Handle a touch event.

Parameters
`v`	View!: The view the touch event has been dispatched to.
`event`	MotionEvent!: The MotionEvent object containing full information about the event.

Return
`Boolean`	True if the listener has consumed the event, false otherwise.