Develop Reference

Difference in behavior of android:gravity="center_vertical" for RelativeLayout and LinearLayout

Let's say I have two views that I want to center vertically. The first view is bigger than the second view.
I noticed that if I place theses two views inside a RelativeLayout with properties layout_height="wrap_content" and android:gravity="center_vertical" nothing happens. This is what I get :
In the opposite, if I place these two views inside a LinearLayour with properties layout_height="wrap_content" and android:gravity="center_vertical" the views are centered vertically :
Lastly, if I place these two views inside a RelativeLayout with properties layout_height with a fixed height and android:gravity="center_vertical" I get the same result as the LinearLayout. The views are centered vertically.
I would expect the views to be centered vertically in each case. Do you know the reason for this difference?

LinearLayout handles all its child object based on its orientation (Horizontal or vertical). So when you are saying gravity: "center_vertical". You are actually referencing based on your parent layout.
In case of RelativeLayout,it enables you to specify the location of child objects relative to each other (child A to the left of child B) or to the parent (aligned to the top of the parent).
Personally I would use gravity only in LinearLayouts and the centerInParent for RelativeLayouts.

In your first case it'll work with RelativeLayout as you expected if you use android:layout_centerVertical="true" to the child view which you want to be centred.
So in case of LinearLayout you need to specify the orientation first (i.e. horizontal/vertical) so that the child views are inflated based on the reference of your parent layout.
While in RelativeLayout, as the name says it all, you can specify the position with respect to the views which are the child of a parent RelativeLayout.
Now the views you want to achieve can be generated in many other ways too.
For example, set your parent layout as LinearLayout. Don't specify any gravity attribute in the parent layout. Hence, you set a layout_gravity attribute to the child to certer_vertical and this should work too.

Well, after some others tests, it seems that the behavior of android:gravity for a RelativeLayout is a bit random. I will just avoid to use is.

Android layout webview between another two views

What's the best approach to have a layout with the following:
Spinner (default height)
WebView (all the space between the two views (Spinner and Button))
Button (default height)
How is it possible to specify the height of the WebView to take all the space between the two (i.e. if they are resized later, the WebView will automatically be adjusted).
Thanks!

Use a RelativeLayout as the parent layout. Align the Spinner to the top of the parent. Align the Button to the bottom of the parent. For the WebView, set the height as match_parent and then use the android:layout_below and android:layout_above attributes to make sure that it always lies between the two views.
(I would've given the code but I don't want to. You might just copy paste with zero learning.)

Add CustomViews to a LayoutView dynamically

I have a LayoutView in a ScrollView named MyLayout and I want to add a View composed by LayoutView with TextView and EdiText inside this ScrollView according a value,
for example with a method
addMyCustomViewToMyLayout(int x){
....
}
that adds the desired number of elements to the MyLayout in the ScrollView,
The CustomViews added to the ScrollView should be linked to the activity to get and set the value from-to the app.
Is possible?
How could I do?

There's nothing very special about ScrollViews. You can think of them as a boundless View. While normal Layouts like a LinearLayout are bound to an area, then ScrollView will allow its child to be whatever height it wants to be (or width in the case of a HorizontalScrollView).
ScrollViews contain one child. The child size is bound by the width of the ScrollView, but it is not bound by the height. Thus, the child will measure itself based on the idea that it has enough vertical space to show everything.
In this case, you create or inflate your MyLayout however you want. Then you add it to the ScrollView. If you want to add other Views to it, you add it to your MyLayout layout view. Just let the ScrollView do its thing.

Android: RemoveAllItems from view doesn't refresh size

I have a ScrollView that contains a LinearLayout.
In code I add items to the LinearLayout and it nicely expands.
When I remove, in code, all the items from the LinearLayout, the LinearLayout stays the same size, it's empty though.
How do I get the ScrollView to reclaim the height that the LinearLayout used when it had items and shrink back the LinearLayout to use the least height as it is now empty?
I have tried (in C#):
linearLayout.RemoveAllViewsInLayout();
linearLayout.PostInvalidate();
scrollView.PostInvalidate();
Java or C# answers are fine.

I only have Java experience with Android, so I would try using:
linearLayout.requestLayout();
This should cause another layout pass, and assuming your LinearLayout is set to WRAP_CONTENT it will measure all the children and size itself to fit the smallest space that the children occupy (or minHeight if you have that set and it is larger).

This trick seems to work. The result is that the linearlayout ids resized and the scrollview as well:
linearLayout.RemoveAllViewsInLayout();
linearLayout.Visibility = ViewStates.Gone;
scrollView.SmoothScrollTo(0, 0);
linearLayout.Visibility = ViewStates.Visible;
There must be a better way, but this works.

How to add more Items in Scrollview in Android?

My android page has 10 EditText and 10 TextView. but there is no space in my screen in the Graphical Layout. i just added 5 only. im using Scroll layout. how to add additional 5 items in the screen without reducing the items height. Is there any coding here.?

<ScrollView>
<LinearLayout>
<TextView/>..
....
..
</LinearLayout>
</ScrollView>
You can add multiple items inside a LinearLayout. Since ScrollView is scrollable it won't affect the dimensions of the Views inside. You can add as many views as you need without worrying about screen size or View size..

You should add a LinearLayout as the only child inside your ScrollView. Then get a reference to that LinearLayout :
mLayout=(LinearLayout)findViewById(R.id.myLayout);
and then add Views dynamically from code using :
EditText et=new EditText(...);
//....
mLayout.addView(et);

A ScrollView can have only one direct child, so you need to put all the other Views in a Layout, such as LinearLayout and put that layout in ScrollView
Make your ScrollView's height as match_parent and the inner LinearLayout's height as wrap_content. The LinearLayout will stretch according to the number of children inside it and if the height exceeds the height of the ScrollView, the overflow can be seen by scrolling. If the ScrollView and inner Layout both have same height or if ScrollView have larger height than inner Layout, the scrolling won't happen for obvious reason.