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How to separate layouts with weightSum in android?

I seem to be having issues understanding weightSum and LayoutWidth. My code is below:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:weightSum="3">
<LinearLayout
android:background="#cccccc"
android:layout_weight="1"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:padding="20sp"
android:textSize="30sp"
android:gravity="center_horizontal"
android:text="Cheapest Fare Option"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
<LinearLayout
android:background="#666666"
android:layout_weight="2"
android:layout_width="match_parent"
android:layout_height="match_parent">
</LinearLayout>
</LinearLayout>
My understanding of this is the 1st layout will take up 1/3 of the space and 2nd layout will take 2/3 of the space, but the reverse is happening, i.e. 1st layout is taking 2/3 and 2nd layout is taking 1/3
Why is this happening? Trying hard to understand this.

Taking your android:orientation="vertical", you want to get this ratio vertically therefore your android:layout_height attribute should be 0dp for both the child LinearLayout.
Set -
android:layout_height="0dp"
for both the inner LinearLayout.
Alternatively if you want to obtain the ratio horizontally then use android:orientation="horizontal" set -
android:layout_width="0dp"
for both the inner LinearLayout.
The thing is when you want to achieve ratio then you don't set that particular dimension (width or height) to match parent. Rather set it to 0dp so that Android can handle it for you automatically.

<LinearLayout
android:background="#cccccc"
android:layout_weight="1"
android:layout_width="match_parent"
android:layout_height="0dp">
<TextView
android:padding="20sp"
android:textSize="30sp"
android:gravity="center_horizontal"
android:text="Cheapest Fare Option"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
<LinearLayout
android:background="#666666"
android:layout_weight="2"
android:layout_width="match_parent"
android:layout_height="0dp">
</LinearLayout>

Understanding weight and layout_weight, the bigger layout_weight is, more it shrinks in the layout.

I am trying to understand the weight layout with this example.
It is definitely not a rocket science. However, this example making it...
The weightSum dictate how big the size is and
Then divide the layout based on layout_weight value for the view in LinearLayout.
In this example I have a layout, weighted with 5, that is then divided between two views:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#color/transactionRowBackground"
android:paddingBottom="5dp"
android:paddingTop="5dp" android:orientation="horizontal" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" android:layout_weight="2" >
<TextView
android:id="#+id/title"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:clickable="true"
android:gravity="top"
android:padding="5dp"
android:text="Test Title"
android:textColor="#color/textColor"
android:textSize="#dimen/subHeadingTextSize"
android:textStyle="bold" />
<TextView
android:id="#+id/description"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:clickable="true"
android:gravity="top"
android:padding="5dp"
android:text="This is a test description"
android:textColor="#color/textColor"
android:textSize="#dimen/normalTextSize" />
</LinearLayout>
<ImageView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="3"
android:src="#drawable/ic_launcher"
android:layout_gravity="top"
android:contentDescription="" />
</LinearLayout>
The thing that I cannot understand is the bigger number I give to ImageViewer the smallest space it get from the parent. So how it is actually calculating the size for ImageView.
You can try with the above xml. If you change the layout weight of an ImageView to 1 , and child linearlayout to 4, that I believe makes more sense, then the opposite will occur.
ImageView will expend and child linearlayout will shrink. I thought the bigger the number is more you get some space.

Since on your outermost layout you have android:orientation="horizontal", I believe you want to vary the size/space taken by ImageView and internal LinearLayout in horizontal direction. For this case try using
android:layout_width="0dp"
on the layouts where you've put android:layout_weight. If your orientation of the outer layout was vertical, I would have used android:layout_height="0dp" in order for the weights to handle width/height of the layouts.
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#color/transactionRowBackground"
android:paddingBottom="5dp"
android:paddingTop="5dp" android:orientation="horizontal" >
<LinearLayout
android:layout_width="0dp"
android:layout_height="wrap_content"
android:orientation="vertical" android:layout_weight="2" >
<TextView
android:id="#+id/title"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:clickable="true"
android:gravity="top"
android:padding="5dp"
android:text="Test Title"
android:textColor="#color/textColor"
android:textSize="#dimen/subHeadingTextSize"
android:textStyle="bold" />
<TextView
android:id="#+id/description"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:clickable="true"
android:gravity="top"
android:padding="5dp"
android:text="This is a test description"
android:textColor="#color/textColor"
android:textSize="#dimen/normalTextSize" />
</LinearLayout>
<ImageView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="3"
android:src="#drawable/ic_launcher"
android:layout_gravity="top"
android:contentDescription="" />
</LinearLayout>
Reading over Android docs might help: Layout Weights

With layout_weight you can specify a size ratio between multiple views. E.g. you have a MapView and a table which should show some additional information to the map. The map should use 3/4 of the screen and table should use 1/4 of the screen. Then you will set the layout_weight of the map to 3 and the layout_weight of the table to 1.
To get it work you also have to set the height or width (depending on your orientation) to 0dp.
Example
If there are three text boxes and two of them declare a weight of 1, while the third one is given no weight (0), then remaining space is assigned as follows:
1st text box = 1/(1+1+0)
2nd text box = 1/(1+1+0)
3rd text box = 0/(1+1+0)

Height of child element as percentage of parent element

I have an EditText tag inside the LinearLayout with horizontal orientation, I want to make height of my EditText as percentage of parent LinearLayout's height. How can this be achieved?
Please don't suggest layout_weight attribute as it will be used to control child elements width not height.

You could write a custom layout that resizes its children to the correct percentages, which is probably the best solution.
Or you could use layout_weight and wrap the EditText in another LinearLayout, something like:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:weightSum="2"
android:orientation="vertical">
<View
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_weight="1"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="0dp"
android:layout_weight="1"
android:text="one"/>
</LinearLayout>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="two"/>
</LinearLayout>

Percentages within a LinearLayout are very easy.
Give your view a weight
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:weightSum="2"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="0dp"
android:layout_weight="0.5"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="0dp"
android:layout_weight="0.25"
android:text="one"/>
</LinearLayout>
I've set the height of the two textViews to 0, but the layout_weight says to make one 50% of the LinearLayout and the other 25% the height of the layout.

Can only LinearLayout specify a fixed-size element with an adjacent element that uses the remaining space?

I'd like to have two adjacent views, a first that is a fixed size and a second that adjacent to the first that uses the remaining space.
I could easily do this with LinearLayout and weights, but I would like to avoid the "nested weights are bad for performance" problem.
Is there another layout type that can accomplish the equivalent? Please provide an example if so.

A RelativeLayout could do what you want, for example:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<Button
android:id="#+id/button1"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:text="Button"
android:background="#99cc00" />
<Button
android:id="#+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_toRightOf="#id/button1"
android:text="Button"
android:background="#0077cc"/>
</RelativeLayout>
The first Button will be 200dp in width and the second will stretch to fill the rest of the parent's remaining width.
You could also use a RelativeLayout to split two views in equal sizes to avoid having double weights on some layouts.

I believe this could be done with a RelativeLayout. Example:
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button
android:id="#+id/button"
android:layout_width="100dp"
android:layout_height="match_parent"
android:layout_alignParentLeft="true" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_toRightOf="#id/button">
...
</LinearLayout>
</RelativeLayout>

You can try
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<Button
android:layout_width="50dp"
android:layout_height="wrap_content"
android:text="view with fixed size " />
<Button
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="view with remaining space" />
</LinearLayout>
this is how weight works in LinearLayout:
At first, it will deduct the fixed dimension, then according to the weight, divide the available space, assign to the views which specify the weight attribute

android:layout_height 50% of the screen size

I just implemented a ListView inside a LinearLayout, but I need to define the height of the LinearLayout (it has to be 50% of the screen height).
<LinearLayout
android:id="#+id/widget34"
android:layout_width="300px"
android:layout_height="235px"
android:orientation="vertical"
android:layout_below="#+id/tv_scanning_for"
android:layout_centerHorizontal="true">
<ListView
android:id="#+id/lv_events"
android:textSize="18sp"
android:cacheColorHint="#00000000"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="#+id/tv_scanning_for"
android:layout_centerHorizontal="true">
</ListView>
</LinearLayout>
Is that possible?
I did something similar for a button and an EditText, but doesn't seem to work on Layouts.
This is my Code:
//capture the size of the devices screen
Display display = getWindowManager().getDefaultDisplay();
double width = display.getWidth();
//my EditText will be smaller than full screen (80%)
double doubleSize = (width/5)*4;
int editTextSize = (int) doubleSize;
//define the EditText
userName = (EditText) this.findViewById(R.id.userName);
password = (EditText) this.findViewById(R.id.password);
//set the size
userName.setWidth(editTextSize);
password.setWidth(editTextSize);

Set its layout_height="0dp"*, add a blank View beneath it (or blank ImageView or just a FrameLayout) with a layout_height also equal to 0dp, and set both Views to have a layout_weight="1"
This will stretch each View equally as it fills the screen. Since both have the same weight, each will take 50% of the screen.
*See adamp's comment for why that works and other really helpful tidbits.

This is easy to do in xml. Set your top container to be a LinearLayout and set the orientation attribute as you wish. Then inside of that place two linearlayouts that both have "fill parent" on width and height. Finally, set the weigth attribute of those two linearlayouts to 1.

This is my android:layout_height=50%
activity:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<LinearLayout
android:id="#+id/alipay_login"
style="#style/loginType"
android:background="#27b" >
</LinearLayout>
<LinearLayout
android:id="#+id/taobao_login"
style="#style/loginType"
android:background="#ed6d00" >
</LinearLayout>
</LinearLayout>
style:
<style name="loginType">
<item name="android:layout_width">match_parent</item>
<item name="android:layout_height">match_parent</item>
<item name="android:layout_weight">0.5</item>
<item name="android:orientation">vertical</item>
</style>

best way is use
layout_height="0dp"
layout_weight="0.5"
for example
<WebView
android:id="#+id/wvHelp"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.5" />
<TextView
android:id="#+id/txtTEMP"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="0.5"
android:text="TextView" />
WebView,TextView have 50% of the screen height

To make sure the height of a view is 50% of the screen then we can create two sub LinearLayouts in a LinearLayout. Each of the child LinearLayout should have "android:layout_weight" of 0.5 to cover half the screen
the parent LinearLAyout should have "android:orientation" set to vertical
.
.
here is code for your reference....
this code contains two buttons of height half the screen
<LinearLayout
android:orientation="vertical"
android:layout_height="match_parent">
<LinearLayout
android:layout_weight="0.5"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:padding="10dp"
android:layout_weight="0.5"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:text="button1"
android:id="#+id/button1"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentBottom="true"
/>
<Button
android:padding="10dp"
android:layout_weight="0.5"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:text="button2"
android:id="#+id/button2"
android:layout_alignParentTop="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_alignParentBottom="true"
/>
</LinearLayout>
<LinearLayout
android:layout_weight="0.5"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
</LinearLayout>
</LinearLayout>

This kind of worked for me.
Though FAB doesn't float independently, but now it isn't getting pushed down.
Observe the weights given inside the LinearLayout
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:id="#+id/andsanddkasd">
<android.support.v7.widget.RecyclerView
android:id="#+id/sharedResourcesRecyclerView"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="4"
/>
<android.support.design.widget.FloatingActionButton
android:id="#+id/fab"
android:layout_width="wrap_content"
android:layout_height="0dp"
android:layout_gravity="bottom|right"
android:src="#android:drawable/ic_input_add"
android:layout_weight="1"/>
</LinearLayout>
Hope this helps :)

You should do something like that:
<LinearLayout
android:id="#+id/widget34"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:layout_below="#+id/tv_scanning_for"
android:layout_centerHorizontal="true">
<ListView
android:id="#+id/lv_events"
android:textSize="18sp"
android:cacheColorHint="#00000000"
android:layout_height="1"
android:layout_width="fill_parent"
android:layout_weight="0dp"
android:layout_below="#+id/tv_scanning_for"
android:layout_centerHorizontal="true"
/>
</LinearLayout>
Also use dp instead px or read about it here.

it's so easy if you want divide your screen two part vertically ( top30% + bottom70%)
<LinearLayout
android:id="#+id/LinearLayoutTop"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="2">
</LinearLayout>
<LinearLayout
android:id="#+id/LinearLayoutBottom"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1">
</LinearLayout>

To achieve this feat, define a outer linear layout with a weightSum={amount of weight to distribute}.
it defines the maximum weight sum. If unspecified, the sum is computed by adding the layout_weight of all of the children. This can be used for instance to give a single child 50% of the total available space by giving it a layout_weight of 0.5 and setting the weightSum to 1.0.Another example would be set weightSum=2, and if the two children set layout_weight=1 then each would get 50% of the available space.
WeightSum is dependent on the amount of children in the parent layout.

You can use android:weightSum="2" on the parent layout combined with android:layout_height="1" on the child layout.
<LinearLayout
android:layout_height="match_parent"
android:layout_width="wrap_content"
android:weightSum="2"
>
<ImageView
android:layout_height="1"
android:layout_width="wrap_content" />
</LinearLayout>