There is a ScrollView and which has many children views. Is there any way to get the offset-y to the top of the ScrollView for every child?
Hmmmm, not sure if this is the quickest, best way to do this, but if you get the view's location on screen, and you know the top of the ScrollView, you can calculate the offset of the view relative to the ScrollView. To get the position of a View in the screen:
int[] location = {0,0};
view.getLocationOnScreen(location);
location[1] has the Y value. You will get negative values when the view is "above" the viewport.
Related
I am trying to get the location on screen of the ListView scrollbar thumb indicator. I'd like to position a label next to it and require the X,Y screen coordinates.
I attempted to get the height of the ListView and use the value from the 'firstVisibleItem' value obtained from the ListView OnScrollListener to position the label but due to the ListView items having varying heights this hasn't proved feasible.
Are there any other solutions to this?
Thanks
I suggest you can use a little bit of hack:
View c = listview.getChildAt(0);
int scrolly = -c.getTop() + listview.getFirstVisiblePosition() * c.getHeight();
But it will work correctly only if you will have same height for all list items.
Current animation changes alpha for every part of view. I want to change the alpha through view's x and y positions. Think it as a growing horizontal bar. I have a view which is drawn by myself (canvas). Also the issue is this drawn views are in list view, they are the listview elements. So probably i need to animate ListView itself not the elements to achieve desired outcome
How can i achieve it?
According to the docs for the View class:
The geometry of a view is that of a rectangle. A view has a location, expressed as a pair of left and top coordinates, and two dimensions, expressed as a width and a height. The unit for location and dimensions is the pixel.
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.
In addition, several convenience methods are offered to avoid unnecessary computations, namely getRight() and getBottom(). These methods return the coordinates of the right and bottom edges of the rectangle representing the view. For instance, calling getRight() is similar to the following computation: getLeft() + getWidth().
My interpretation of the above is that the View's position is controlled by its "Left" and "Top" values, while its width and height are controlled by its "Width" and "Height" values. This seems especially clear considering that last sentence, where "Right" is derived by adding Left and Width.
Despite this, when I use setLeft() and/or setTop() to change the position of the View, the SIZE of the View changes on screen! Meanwhile, the lower right corner of the View stays anchored to its original spot. This behavior implies that "Right" and "Bottom" are actual values, not derived as described in the docs.
So what is really going on here? The docs say one thing, but the behavior says the opposite. What is the proper way to reposition a View?
EDIT: I added a RelativeLayout:
myParams = new RelativeLayout.LayoutParams(300,300);
myParams.addRule(RelativeLayout.CENTER_HORIZONTAL);
myParams.addRule(RelativeLayout.CENTER_VERTICAL);
myView.setLayoutParams(myParams);
...to create a View 300x300 centered on the screen. Works perfectly. But examining that RelativeLayout, the location seems to be controlled by leftMargin and topMargin - yet both are zero! That raises the questions of 1) how can you examine the LayoutParams to know where the View is right now, and 2) how can you alter the LayoutParams to move it to a different location?
EDIT: As an experiment, I added an onTouch method to the View and did this within it (excerpt):
if (MotionEvent.ACTION_MOVE == iAction) {
myParams = (RelativeLayout.LayoutParams) v.getLayoutParams();
myParams.leftMargin = 0;
myParams.topMargin = 0;
v.setLayoutParams(myParams);
}
...on the theory that my vertically and horizontally centered View would then move to the upper left corner of the screen. Result: It didn't move at all. Not exactly surprising, since .leftMargin and .topMargin were already zero, but I wanted to try it just in case there was some magic hiding here.
Other suggestions?
I am facing the same problem in this question, but I have difficulty in understanding the exact meaning of the four position parameters in layout(int l, int t, int r, int b). I know they represent left, top, right and bottom respectively relative to parent, but "relative" to where exactly?
For example, if I translate the button down 100 pixel, in order to move the clickable area down 100 pixel should I set
// l t r b
button.layout(0, 100, 0, button.getHeight()+100)
? Does the integer 100 of second parameter mean 100 pixel down relative to the top of parent? Is the fourth parameter means button.getHeight()+100 relative to the top of parent also??? I tested on my device, the clickable area does not move down as I want. I'm very confused here, any help is greatly appreciated.
The parameters to layout are relative to the parent view's upper left corner. X increases as you move to the right and Y increases as you move down. It is not relative to the view's current position.
You probably don't want to call layout on a child view outside of its parent's onLayout method. There are several other bits of internal bookkeeping that happen as a result of calling layout that will change internal state in a way you don't want for simple animations.
Typically layout is called like this:
child.layout(x, y, x + child.getMeasuredWidth(), y + child.getMeasuredHeight());
The parameters are absolute, with (0, 0) at the parent's upper left corner.
But if you're simply moving a view around for animation you probably want to do something more like:
// Adjust horizontally; dx = change in x position
child.offsetLeftAndRight(dx);
// Adjust vertically; dy = change in y position
child.offsetTopAndBottom(dy);
The parameters to the offset* methods are relative to the view's current position.
If you write a ViewGroup class that moves its child views around in this way, remember that you can get a layout request at any time. At that point your ViewGroup's onLayout method will try to position the child based on its usual layout rules and it will need to adjust this positioning to reflect any other accumulated movement you want to preserve.
I want to get position of view located inside a RelativeLayout ?
You can use getLocationOnScreen method to detect position of your view and layout on screen. Then just calculate relative coordinates.