Android Basics

Layout Design[UI Design]
Each UI layout file must contain exactly one root element like textview or 
or edittext or button, which must be a View or ViewGroup object. Once we defined 
the root element, we can add additional layout objects or widgets as 
child elements to gradually build a View hierarchy that defines our layout. 
 
 
 
Example : The XML layout that uses a vertical LinearLayout to hold a 
 Button and a Edittext.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:orientation="vertical" >
              
            <Button android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello, I am a Button" />
            
            <EditText android:id="@+id/edittext"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="Hello, I am a EditText" />
   
</LinearLayout>


 Example : The XML layout that uses a Horizontal Linearlayout to
 hold a Edittext and a Button

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >
    <EditText android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, I am a EditText" />
    <Button android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, I am a Button" />
</LinearLayout>




 Example : The XML layout that uses a vertical Relative to
 hold a Edittext and a Button.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
     >
    <EditText android:id="@+id/edittext"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, I am a EditText" />
    <Button android:id="@+id/button"
        android:layout_below="@+id/edittext"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello, I am a Button" />
</RelativeLayout>