Set position / size of UI element as percentage of screen size
I think what you want is to set the android:layout_weight,
http://developer.android.com/resources/tutorials/views/hello-linearlayout.html
something like this (I'm just putting text views above and below as placeholders):
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:weightSum="1">
<TextView
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="68"/>
<Gallery
android:id="@+id/gallery"
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="16"
/>
<TextView
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="16"/>
</LinearLayout>
Use the PercentRelativeLayout or PercentFrameLayout from the Percent Supoort Library
<android.support.percent.PercentFrameLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="match_parent"
app:layout_heightPercent="68%"/>
<Gallery
android:id="@+id/gallery"
android:layout_width="match_parent"
app:layout_heightPercent="16%"/>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_width="match_parent"/>
</android.support.percent.PercentFrameLayout>
For TextView and it's descendants (e.g., Button) you can get the display size from the WindowManager and then set the TextView height to be some fraction of it:
Button btn = new Button (this);
android.view.Display display = ((android.view.WindowManager)getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
btn.setHeight((int)(display.getHeight()*0.68));
The above problem can also be solved using ConstraintLayout through Guidelines.
Below is the snippet.
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.constraint.Guideline
android:id="@+id/upperGuideLine"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_percent="0.68" />
<Gallery
android:id="@+id/gallery"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="@+id/lowerGuideLine"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="@+id/upperGuideLine" />
<android.support.constraint.Guideline
android:id="@+id/lowerGuideLine"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_percent="0.84" />
</android.support.constraint.ConstraintLayout>