Placing the components of a LinearLayout

The purpose of layout is to arrange the various components within itself according to a particular scheme and the LinearLayout is the simplest of layout which is proposed by default when you create an Android project.

1. Create a new Android project
2. Edit the file res/layout/main.xml:

   <?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" >
       
       <TextView
           android:id="@+id/textView1"
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           android:layout_weight="1"
           android:gravity="top|left"
           android:background="@color/yellow"
           android:text="@string/label1"/>
       
       <TextView
           android:id="@+id/textView1"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_weight="2"
           android:layout_gravity="center"
           android:gravity="center"
           android:background="@color/green"
           android:layout_margin="50px"
           android:text="@string/label2"/>
           
       <TextView
           android:id="@+id/textView1"
           android:layout_width="match_parent"
           android:layout_height="wrap_content"
           android:layout_weight="3"
           android:gravity="bottom|right"
           android:padding="50px"
           android:background="@color/fuchsia"
           android:text="@string/label3"/>
               
   </LinearLayout>
   

3. Edit the file res/values/strings.xml:

   <?xml version="1.0" encoding="utf-8"?>
   <resources>
   
       <string name="hello">Hello World, LinearLayoutTutorialActivity!</string>
       <string name="app_name">LinearLayoutTutorial</string>
       <string name="label1">one</string>
       <string name="label2">two</string>
       <string name="label3">three</string>
   
   </resources>
   

4. Create the file res/values/colors.xml:

   <?xml version="1.0" encoding="utf-8"?>
   <resources>
    <color name="yellow">#FFFF00</color>
    <color name="fuchsia">#FF00FF</color>
    <color name="green">#008000</color>
   </resources>
   

5. Verify that the main class has the method:

       public void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.main);
       }
   

The end result seen by the emulator is as follows:

The Linearlayout arrange the components in or portrait or landscape orientation, you can verify this aspect replacing android: orientation = “vertical” with android: orientation = “vertical”in the file main.xml.
The dimensions of the components are mainly determined by android:layout_width and layout_height whose values can be set to:

• fill_parent: the component fills all available space (deprecated)
• match_parent: the component fills all available space
• wrap_content: the component gets enough space to show their contents
• [a number]: specify an exact number in px (pixels), dp (density-independent pixels), sp (scaled pixels based on preferred font size), in (inches), mm (millimeters)

The dimensions of the components can be increased or decreased value to android:layout_weight, and the components for which a value is specified for android:layout_weight have relative size proportionate to that value.
android:layout_gravity e android:gravity set similar characteristics but on different objects:

• android:layout_gravity: sets the positioning of the component relative to the layout
• android:gravity: sets the positioning of the body of the component relative to the same component.

You can specify multiple values separated by the character “|”, for example: android:gravity=”bottom|center”.
android:padding sets the distance between the body of the component and the edge of the component.
android:layout_margin sets the distance between the component from the edge of the layout or other elements.
android:padding e android:layout_margin can also be set for layout.