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LinearLayout with percent empty space

I am working on linear layout for my simple android application. I wanna make the portion of two views dynamically change based on the size ( I want to have, for a row for left to right, the first 20% is empty, and all the content is inside the rest of 80%) . For this approach, i chosen the weight for different view. I created an nested linear layout for this approach. For example, the layout hierarchy is something like this.
<linearLayout> //parent layout
<linearLayout //child 1 layout
android:layout_weight="1">
//so that this view occupy 20% of the space regardless the width of device. I intensionally wanna keep this view empty.
</linearLayout>
<linearLayout //child 2 layout
android:layout_weight="4">
//so that this view occupy 80% of the space regardless the width of device. and
//inside this view I have whatever view I wanna add on it.
<EditText>
<ImageView>
</linearLayout>
</linearLayout>
With this approach, the Lint in Android Studio tell me the following warnings:
This is a Nested Layout. Layout weights require a widget to be measured twice. When a LinearLayout with non-zero weights is nested inside another LinearLayout with non-zero weights, then the number of measurements increase exponentially.
the child 1 layout is useless: This LinearLayout view is useless (no children, no background, no id, no style)
Can anyone address me the right layout to use in order to have the layout dynamically change based on the size of devices? How should I correctly set up the empty space for a linear layout case?

This is a possible solution using weights:
<LinearLayout
android:layout_width="match_parent"
android:gravity="end"
android:weightSum="1">
<!-- Your content here: -->
<View
android:layout_width="0dp"
android:layout_weight="0.8"
android:layout_gravity="end" />
</LinearLayout>

Have a look at PercentRelativeLayout.
Note: You need the Percent library to use it.

What does FrameLayout do?

I'm new to programming. I was using Graphical Layout then when I was reading xml file, I saw FrameLayout. Then I searched, but I couldn't find something useful. What is FrameLayout and what does it do?

You use a FrameLayout to stack child views on top of each other, with the most recent child on top of the stack. In the example below, the TextView is the most recent, so it is automatically placed on top of the ImageView.
For example:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:id="#+id/backgroundImage"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:scaleType="centerCrop"
android:src="#drawable/bitmapie" />
<TextView
android:id="#+id/descTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:layout_marginTop="70dp"
android:background="#android:color/holo_blue_light"
android:padding="10dp"
android:text="TextView placed at the top of the Imageview"
android:textColor="#android:color/white"
android:textSize="22sp" />
</FrameLayout>
Output:

FrameLayout is the simplest implementation of ViewGroup. Child views are drawn are in a stack, where the latest added view is drawn at the top. Usually you can use one of the next approaches or combine them:
Add a single view hierarchy into FrameLayout
Add multiple children and use android:layout_gravity to navigate them
Another popular approaches of using FrameLayout:
as a Fragment container
as an ancestor of your custom ViewGroup

You can consider the word frame as regular photo frame. What you do with that frame? you can place photos in that frame by one top to another. Same as in FrameLayout we can place views ( Any layout, or widget like button, text, image so on) top of other as #ojonugwa shows you the textview top of the Image.

Are you sure that you googled it?
http://www.tutorialspoint.com/android/android_frame_layout.htm
Frame Layout is designed to block out an area on the screen to display a single item. Generally, FrameLayout should be used to hold a single child view, because it can be difficult to organize child views in a way that's scalable to different screen sizes without the children overlapping each other.
You can, however, add multiple children to a FrameLayout and control
their position within the FrameLayout by assigning gravity to each
child, using the android:layout_gravity attribute.
http://blog.neteril.org/blog/2013/10/10/framelayout-your-best-ui-friend/
The secret of FrameLayout is how it layouts its children. Although normally designed to contain one
item, it will happily stack up other element on top of each other.
Thus FrameLayout is essentially a way to manipulate the Z-order of
views on the screen.
This is super useful for a couple of UI tricks from HUD-like elements
to sliding panels to more complex animated transitions. In this post
we will see an example for each of those.
http://www.learn-android-easily.com/2013/05/frame-layout-in-androis.html
FrameLayout is designed to display a single item at a time. You can
have multiple elements within a FrameLayout but each element will be
positioned based on the top left of the screen. Elements that overlap
will be displayed overlapping. I have created a simple XML layout
using FrameLayout that shows how this works.

Basically it puts one view on top of another for example :
Inflating text on Image
<FrameLayout>
<ImageView>
<Textview>
</FrameLayout>

Android layout overlap buttons on top of eachother (same center)

So the initial layout consists of a large circular "parent" button and multiple circular "child" buttons that are centered behind the parent button. So all the child buttons share the same center as the parent button. The reason for this layout is so during runtime, I can move the child buttons in and out of the parent button using translateX and translateY.
However, I'm stuck on the initial layout. How can I center the child buttons to the center of the parent button without hardcoding any child attributes?

Make the views the same size and add padding to the children so they get reduced. If the views are all in the same position the layout will look as you wish. Anyways, you can always change the properties in code.

I solved this myself using a container RelativeLayout as an anchor, with the parent button and all child buttons given android:layout_centerInParent. Then, to solve the issue of the child buttons disappearing when leaving the container, I gave the container android:clipChildren(false) and also set clipChildren to false on all of its ancestors as well.
Note that the container has to be bigger than all of its child elements, or all the child elements will be clipped to the same dimensions, even when they move outside of the container! To solve this, I gave the container a width and height of wrap_content.
Thus, all my child buttons were centered in the parent button no matter where I positioned the parent, and the child buttons were free to move around as well.
EDIT
A major flaw in this is that buttons can't recieve touch events if they are outside of their parent. To fix this, you can either use event coordinates or make the parent container big enough to always encompass the child elements (maybe twice the screen width/height?)
Here is the code:
res/layout/listfragment.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipChildren="false" >
<ListView
android:id="#android:id/list"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<RelativeLayout
android:onClick="onButterflyMenuClicked"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|right"
android:layout_marginBottom="20sp"
android:layout_marginRight="15sp"
android:clipChildren="false" >
<Button
android:id="#+id/btn_north_1"
style="#style/PeekabooButton"
android:text="1st"
android:translationY="-65sp" />
<Button
android:id="#+id/btn_north_2"
style="#style/PeekabooButton"
android:text="2nd"
android:translationY="-115sp" />
<Button
android:id="#+id/kingbutton"
android:layout_width="65sp"
android:layout_height="65sp"
android:layout_centerInParent="true"
android:gravity="center_vertical|center_horizontal"
android:textSize="16sp"
android:text="KING" />
</RelativeLayout>
</FrameLayout>
res/values/styles.xml
<style name="PeekabooButton">
<item name="android:layout_width">45sp</item>
<item name="android:layout_height">45sp</item>
<item name="android:layout_centerInParent">true</item>
<item name="android:textSize">10sp</item>
</style>

Use android:gravity="center" on all views after putting them all inside a FrameLayout (possibly nesting the FrameLayout inside another layout). You can then offset each Button's position in its parent by changing the layout_margin* values. Or you could translate the parent FrameLayout that holds all the Buttons however you wish.
To make the button circular, change your button's android:background value to point to a custom selector.

How to float/overlap a view in android?

I have many activities with a scrollview inside a tablelayout. However, it is necessary a small design change, so I have to put a black transparent view over the whole screen from the top to the bottom. Is it possible to do it in the tablelayout or the scrollview?

RelativeLayout allows for easy overlapping of views. You'll have to adjust the existing views in your app because it doesn't do anything automatically.
EDIT:
A quick way to do this would be to take your existing view (the ScrollView) that is already organized and put it in a top-level RelativeLayout. Then, all you have to do is add new view inside the RelativeLayout with the width and height both set to MATCH_PARENT. The result should be the black transparent view will be visible over the ScrollView.

I normally use FrameLayout to achieve any kind of 'layering' of views.
<FrameLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
//your existing layout
<View
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#33000000" />
</FrameLayout>
As DeeV said, you can probably use RelativeLayout in a similar way, but you might have to set additional attributes on its children to achieve this.

android: how to make a child view overlap the parent?

I need to implement the layout as in the picture. Parent and Sibling are in a vertical LinearLayout. So I need to make a child view to overlap it's parent. Can I do that in android?

If:
sibling is a sibling of parent
parent is a ViewGroup
and you really want child to be a child of parent
then maybe you could consider using android:clipChildren set to false on parent.

I was actually just looking at an example of a FrameLayout that had a TextView overlaid on top of an ImageView. So, there are obviously multiple ways to get it done. Your next question might be which one is best ... to that I have no idea, but here's a guy that might:
http://www.curious-creature.org/2009/03/01/android-layout-tricks-3-optimize-part-1/

Just contain them all within a RelativeLayout, and remember the draw order is top to bottom, so put the top most view on the bottom of the XML definition.

If you use a RelativeLayout you should have no problem achieving this effect. By default it will stack all of its children on top of each other in the top left corner if you don't supply them with android:layout parameters. So it will definitely support overlapping children. You'd just have to figure out what the best way to tell it where the child should go on the screen relative to something else.

There are at least two layouts that can do that. AbsoluteLayout and RelativeLayout. I suggest that you put your views in a RelativeLayout and add them with LayoutParams that specify their offset form the top and left of the parent:
RelativeLayout.LayoutParams rlp;
label = new TextView(ctx);
label.setBackgroundColor(0x00000000);
label.setTextColor(0xFF7ea6cf);
label.setTextSize(13);
label.setGravity(Gravity.LEFT);
label.setText("Examples:\n- Fentanyl\n- Dilaudid 2 mg PO q 4 hours prn moderate pain");
rlp = new RelativeLayout.LayoutParams(LayoutParams.FILL_PARENT,100);
rlp.topMargin=189;
rlp.leftMargin=30;
rlp.rightMargin=30;
rlParent.addView(label,rlp);

In my case, I have to set android:clipCildren to be false on the parent of parent.
i.e.
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipChildren="false"
android:id="#+id/parent1">
<FrameLayout
android:id="#+id/parent2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="64dp"
android:background="#android:color/holo_blue_bright">
<View
android:id="#+id/This_is_the_view_I_want_to_overlap_parent2"
android:layout_width="160dp"
android:layout_height="80dp"
android:layout_gravity="top|start"
android:layout_marginTop="-40dp"
android:background="#000000" />
</FrameLayout>
</FrameLayout>