Unity3D UI, calculation for position dragging an item?
I would make your script implement the drag interfaces
public class Dragster:MonoBehaviour,IBeginDragHandler, IEndDragHandler, IDragHandler
Which will make your DragIt function become
public void OnDrag(PointerEventData eventData)
{
transform.position += (Vector3)eventData.delta;
}
giving you access to the delta of that event (how much the mouse has moved) to be able to move your object.
If you would still rather use the EventTrigger component (less prefered way), you just need to change your DragIt function to DragIt(PointerEventData eventData) and use the Dynamic EvenData option in the drop down for the trigger to receive the PointerEventData to access the delta information
Here's actually a total, complete, solution for drag and drop 'UnityEngine.UI` items, based on Uri & Colton's code. Just copy and paste.
Astounding copy and paste no-brainer perfect drag and drop for Unity UI, wtt Colton & Uri:
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;
public class UNCDraggable:MonoBehaviour,
IBeginDragHandler, IDragHandler, IEndDragHandler, IDropHandler
{
public Image ghost;
// note DON'T try to drag the actual item: it's not worth the hassle.
// a problem arises where you can't have it on top (as you would want
// visually), and still easily get the drops. always use a ghost.
// even if you want the "original invisible" while dragging,
// simply hide it and use a ghost. everything is tremendously
// easier if you do not move the originals.
void Awake()
{
ghost.raycastTarget = false;
// (just in case you forgot to do that in the Editor)
ghost.enabled = false;
}
public void OnBeginDrag(PointerEventData eventData)
{
ghost.transform.position = transform.position;
ghost.enabled = true;
}
public void OnDrag(PointerEventData eventData)
{
ghost.transform.position += (Vector3)eventData.delta;
}
public void OnEndDrag(PointerEventData eventData)
{
ghost.enabled = false;
}
public void OnDrop(PointerEventData data)
{
GameObject fromItem = data.pointerDrag;
if (data.pointerDrag == null) return; // (will never happen)
UNCDraggable d = fromItem.GetComponent<UNCDraggable>();
if (d == null)
{
// means something unrelated to our system was dragged from.
// for example, just an unrelated scrolling area, etc.
// simply completely ignore these.
return;
// note, if very unusually you have more than one "system"
// of UNCDraggable items on the same screen, be careful to
// distinguish them! Example solution, check parents are same.
}
Debug.Log ("dropped " + fromItem.name +" onto " +gameObject.name);
// your code would look probably like this:
YourThings fromThing = fromItem.GetComponent<YourButtons>().info;
YourThings untoThing = gameObject.GetComponent<YourButtons>().info;
yourBossyObject.dragHappenedFromTo(fromThing, untoThing);
}
}
First of all, All the other anwers in this post are working very well. I worked on this for so long and just wanted to post it here. It adds a way prevent other unwanted UI objects to be dragged around.
My official goal was to provide a way to do this without using bool beingDragged = false;. You just won't know which Button or Image is being dragged if you do it like that.
Dragging UI:
Convert Screenpoint to Local point in the RectTransform with help of RectTransformUtility then use Canvas.transform.TransformPoint to find out where exactly the child UI is.
public Canvas parentCanvasOfImageToMove;
Vector2 pos;
RectTransformUtility.ScreenPointToLocalPointInRectangle(parentCanvasOfImageToMove.transform as RectTransform, eventData.position, parentCanvasOfImageToMove.worldCamera, out pos);
UIToMove.transform.position = parentCanvasOfImageToMove.transform.TransformPoint(pos);
The drag code looks more complicated than other drag code in other answers but it seems to be working in every Canvas camera mode.
Detecting which Object is about to be dragged:
The easiest way of doing this is to create a global variable you can use to save which object user wants to drag in the OnBeginDrag function then you can drag that object in the OnDrag. Set that object to null when OnEndDrag is called.
objectToBeDragged = eventData.pointerCurrentRaycast.gameObject;
This must be done once in the OnBeginDrag function then saved to a global variable.
You can't do the following in the OnDrag function
if (eventData.pointerCurrentRaycast.gameObject == someOtherUI)
{
someOtherUI....drag
}
Even though it is suppose to work, it doesn't sometimes. It even return null sometimes during OnDrag. That's why it has to be done in the OnBeginDrag function.
Detecting and Dragging Button Vs Image:
Detecting if the UI is just an Image and Dragging an Image is very easy.
objectToBeDragged = eventData.pointerCurrentRaycast.gameObject;
Button tempButton = objectToBeDragged.GetComponent<Button>();
Image tempImage = objectToBeDragged.GetComponent<Image>();
If tempImage is not null and tempButton is null then that is an Image.
Detecting if the UI is just a Button and Dragging a Button is NOT easy.
When a Button is clicked on the side/edge, the name of the Button is returned which is fine. But most of the times, a click on a Button happens in the middle of the Button which does not return the instance or name of the Button but instead returns the Text(Child Object). You CANNOT move a text as a Button. It wont work.
objectToBeDragged = eventData.pointerCurrentRaycast.gameObject;
Button tempButton = objectToBeDragged.GetComponent<Button>();
Image tempImage = objectToBeDragged.GetComponent<Image>();
Text tempText = objectToBeDragged.GetComponent<Text>();
if tempText is not null, get GetComponentInParent of Image and Button component of the Text. If the Image is not null and Button is not null then it is a Button.
if (tempText != null)
{
tempButton = tempText.GetComponentInParent<Button>();
tempImage = tempText.GetComponentInParent<Image>();
if (tempButton != null && tempImage != null)
{
//This is a Button
}
}
Below is the complete script of dragging UI Image/Panel and Button. Any Button that should be dragged should be put in the UIButtons array and any Panel/Image that should be dragged should be put in the UIPanels array. It will ignore other UI that are not in the Array.
public class UIDRAGGER : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
public Canvas parentCanvasOfImageToMove;
//10 UI Buttons (Assign in Editor)
public Button[] UIButtons;
//2 UI Panels/Images (Assign in Editor)
public Image[] UIPanels;
//Hold which Button or Image is selected
private Button selectedButton;
private Image selectedUIPanels;
//Used to make sure that the UI is position exactly where mouse was clicked intead of the default center of the UI
Vector3 moveOffset;
//Used to decide which mode we are in. Button Drag or Image/Panel Mode
private DragType dragType = DragType.NONE;
void Start()
{
parentCanvasOfImageToMove = gameObject.GetComponent<Canvas>();
}
//Checks if the Button passed in is in the array
bool buttonIsAvailableInArray(Button button)
{
bool _isAValidButton = false;
for (int i = 0; i < UIButtons.Length; i++)
{
if (UIButtons[i] == button)
{
_isAValidButton = true;
break;
}
}
return _isAValidButton;
}
//Checks if the Panel/Image passed in is in the array
bool imageIsAvailableInArray(Image image)
{
bool _isAValidImage = false;
for (int i = 0; i < UIPanels.Length; i++)
{
if (UIPanels[i] == image)
{
_isAValidImage = true;
break;
}
}
return _isAValidImage;
}
void selectButton(Button button, Vector3 currentPos)
{
//check if it is in the image array that is allowed to be moved
if (buttonIsAvailableInArray(button))
{
//Make the image the current selected image
selectedButton = button;
dragType = DragType.BUTTONS;
moveOffset = selectedButton.transform.position - currentPos;
}
else
{
//Clear the selected Button
selectedButton = null;
dragType = DragType.NONE;
}
}
void selectImage(Image image, Vector3 currentPos)
{
//check if it is in the image array that is allowed to be moved
if (imageIsAvailableInArray(image))
{
//Make the image the current selected image
selectedUIPanels = image;
dragType = DragType.IMAGES;
moveOffset = selectedUIPanels.transform.position - currentPos;
}
else
{
//Clear the selected Button
selectedUIPanels = null;
dragType = DragType.NONE;
}
}
public void OnBeginDrag(PointerEventData eventData)
{
GameObject tempObj = eventData.pointerCurrentRaycast.gameObject;
if (tempObj == null)
{
return;
}
Button tempButton = tempObj.GetComponent<Button>();
Image tempImage = tempObj.GetComponent<Image>();
Text tempText = tempObj.GetComponent<Text>();
//For Offeset Position
Vector2 pos;
RectTransformUtility.ScreenPointToLocalPointInRectangle(parentCanvasOfImageToMove.transform as RectTransform, eventData.position, parentCanvasOfImageToMove.worldCamera, out pos);
//Button must contain Text then Image and Button as parant
//Check if this is an image
if (tempButton == null || tempImage == null)
{
//Button not detected. Check if Button's text was detected
if (tempText != null)
{
//Text detected. Now Look for Button and Image in the text's parent Object
tempButton = tempText.GetComponentInParent<Button>();
tempImage = tempText.GetComponentInParent<Image>();
//Since child is text, check if parents are Button and Image
if (tempButton != null && tempImage != null)
{
//This is a Button
selectButton(tempButton, parentCanvasOfImageToMove.transform.TransformPoint(pos));
}
//Check if there is just an image
else if (tempImage != null)
{
//This is an Image
selectImage(tempImage, parentCanvasOfImageToMove.transform.TransformPoint(pos));
}
}
else
{
//This is an Image
selectImage(tempImage, parentCanvasOfImageToMove.transform.TransformPoint(pos));
}
}
//Check if there is just an image
else if (tempImage != null)
{
selectImage(tempImage, parentCanvasOfImageToMove.transform.TransformPoint(pos));
}
}
public void OnDrag(PointerEventData eventData)
{
Vector2 pos;
if (dragType == DragType.BUTTONS)
{
RectTransformUtility.ScreenPointToLocalPointInRectangle(parentCanvasOfImageToMove.transform as RectTransform, eventData.position, parentCanvasOfImageToMove.worldCamera, out pos);
selectedButton.transform.position = parentCanvasOfImageToMove.transform.TransformPoint(pos) + moveOffset;
}
else if (dragType == DragType.IMAGES)
{
RectTransformUtility.ScreenPointToLocalPointInRectangle(parentCanvasOfImageToMove.transform as RectTransform, eventData.position, parentCanvasOfImageToMove.worldCamera, out pos);
selectedUIPanels.transform.position = parentCanvasOfImageToMove.transform.TransformPoint(pos) + moveOffset;
}
}
public void OnEndDrag(PointerEventData eventData)
{
//Buttons
if (dragType == DragType.BUTTONS || dragType == DragType.IMAGES)
{
selectedButton = null;
selectedUIPanels = null;
dragType = DragType.NONE;
}
}
DragType getCurrentDragType()
{
return dragType;
}
private enum DragType { NONE, BUTTONS, IMAGES };
}