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android – Getting View's coordinates relative to the root layout

Posted by: admin March 11, 2020 Leave a comment

Questions:

Can I get a View’s x and y position relative to the root layout of my Activity in Android?

How to&Answers:

This is one solution, though since APIs change over time and there may be other ways of doing it, make sure to check the other answers. One claims to be faster, and another claims to be easier.

private int getRelativeLeft(View myView) {
    if (myView.getParent() == myView.getRootView())
        return myView.getLeft();
    else
        return myView.getLeft() + getRelativeLeft((View) myView.getParent());
}

private int getRelativeTop(View myView) {
    if (myView.getParent() == myView.getRootView())
        return myView.getTop();
    else
        return myView.getTop() + getRelativeTop((View) myView.getParent());
}

Let me know if that works.

It should recursively just add the top and left positions from each parent container.
You could also implement it with a Point if you wanted.

Answer:

The Android API already provides a method to achieve that.
Try this:

Rect offsetViewBounds = new Rect();
//returns the visible bounds
childView.getDrawingRect(offsetViewBounds);
// calculates the relative coordinates to the parent
parentViewGroup.offsetDescendantRectToMyCoords(childView, offsetViewBounds); 

int relativeTop = offsetViewBounds.top;
int relativeLeft = offsetViewBounds.left;

Here is the doc

Answer:

Please use view.getLocationOnScreen(int[] location); (see Javadocs). The answer is in the integer array (x = location[0] and y = location[1]).

Answer:

No need to calculate it manually.

Just use getGlobalVisibleRect like so:

Rect myViewRect = new Rect();
myView.getGlobalVisibleRect(myViewRect);
float x = myViewRect.left;
float y = myViewRect.top;

Also note that for the centre coordinates, rather than something like:

...
float two = (float) 2
float cx = myViewRect.left + myView.getWidth() / two;
float cy = myViewRect.top + myView.getHeight() / two;

You can just do:

float cx = myViewRect.exactCenterX();
float cy = myViewRect.exactCenterY();

Answer:

View rootLayout = view.getRootView().findViewById(android.R.id.content);

int[] viewLocation = new int[2]; 
view.getLocationInWindow(viewLocation);

int[] rootLocation = new int[2];
rootLayout.getLocationInWindow(rootLocation);

int relativeLeft = viewLocation[0] - rootLocation[0];
int relativeTop  = viewLocation[1] - rootLocation[1];

First I get the root layout then calculate the coordinates difference with the view.
You can also use the getLocationOnScreen() instead of getLocationInWindow().

Answer:

You can use `

view.getLocationOnScreen(int[] location)

;` to get location of your view correctly.

But there is a catch if you use it before layout has been inflated you will get wrong position.

Solution to this problem is adding ViewTreeObserver like this :-

Declare globally the array to store x y position of your view

 int[] img_coordinates = new int[2];

and then add ViewTreeObserver on your parent layout to get callback for layout inflation and only then fetch position of view otherwise you will get wrong x y coordinates

  // set a global layout listener which will be called when the layout pass is completed and the view is drawn
            parentViewGroup.getViewTreeObserver().addOnGlobalLayoutListener(
                    new ViewTreeObserver.OnGlobalLayoutListener() {
                        public void onGlobalLayout() {
                            //Remove the listener before proceeding
                            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                                parentViewGroup.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                            } else {
                                parentViewGroup.getViewTreeObserver().removeGlobalOnLayoutListener(this);
                            }

                            // measure your views here
                            fab.getLocationOnScreen(img_coordinates);
                        }
                    }
            );

and then use it like this

xposition = img_coordinates[0];
yposition =  img_coordinates[1];

Answer:

I wrote myself two utility methods that seem to work in most conditions, handling scroll, translation and scaling, but not rotation. I did this after trying to use offsetDescendantRectToMyCoords() in the framework, which had inconsistent accuracy. It worked in some cases but gave wrong results in others.

“point” is a float array with two elements (the x & y coordinates), “ancestor” is a viewgroup somewhere above the “descendant” in the tree hierarchy.

First a method that goes from descendant coordinates to ancestor:

public static void transformToAncestor(float[] point, final View ancestor, final View descendant) {
    final float scrollX = descendant.getScrollX();
    final float scrollY = descendant.getScrollY();
    final float left = descendant.getLeft();
    final float top = descendant.getTop();
    final float px = descendant.getPivotX();
    final float py = descendant.getPivotY();
    final float tx = descendant.getTranslationX();
    final float ty = descendant.getTranslationY();
    final float sx = descendant.getScaleX();
    final float sy = descendant.getScaleY();

    point[0] = left + px + (point[0] - px) * sx + tx - scrollX;
    point[1] = top + py + (point[1] - py) * sy + ty - scrollY;

    ViewParent parent = descendant.getParent();
    if (descendant != ancestor && parent != ancestor && parent instanceof View) {
        transformToAncestor(point, ancestor, (View) parent);
    }
}

Next the inverse, from ancestor to descendant:

public static void transformToDescendant(float[] point, final View ancestor, final View descendant) {
    ViewParent parent = descendant.getParent();
    if (descendant != ancestor && parent != ancestor && parent instanceof View) {
        transformToDescendant(point, ancestor, (View) parent);
    }

    final float scrollX = descendant.getScrollX();
    final float scrollY = descendant.getScrollY();
    final float left = descendant.getLeft();
    final float top = descendant.getTop();
    final float px = descendant.getPivotX();
    final float py = descendant.getPivotY();
    final float tx = descendant.getTranslationX();
    final float ty = descendant.getTranslationY();
    final float sx = descendant.getScaleX();
    final float sy = descendant.getScaleY();

    point[0] = px + (point[0] + scrollX - left - tx - px) / sx;
    point[1] = py + (point[1] + scrollY - top - ty - py) / sy;
}

Answer:

I just found the answer here

It says:
It is possible to retrieve the location of a view by invoking the methods getLeft() and getTop(). The former returns the left, or X, coordinate of the rectangle representing the view. The latter returns the top, or Y, coordinate of the rectangle representing the view. These methods both return the location of the view relative to its parent. For instance, when getLeft() returns 20, that means the view is located 20 pixels to the right of the left edge of its direct parent.

so use:

view.getLeft(); // to get the location of X from left to right
view.getRight()+; // to get the location of Y from right to left

Answer:

Incase someone is still trying to figure this out. This is how you get the center X and Y of the view.

    int pos[] = new int[2];
    view.getLocationOnScreen(pos);
    int centerX = pos[0] + view.getMeasuredWidth() / 2;
    int centerY = pos[1] + view.getMeasuredHeight() / 2;