As
discussed in the previous chapter that layouts are used to create User
Interface for our Android Applications and inflated in the Activity class using
setContentView() method
The
basic building blocks of Android user interface is View. Each views has attributes/properties. Attributes defines
the look of the views. Some of the important and frequently used views in Android are Layout,
TextView, EditText, Button,CheckBoxes, Radio Buttons, Progress bar etc. How to
use these views and how to handle the click and other events on these views
will be discussed in detail in next chapter.
In this
chapter we will discuss about Layout and their types.
Before
going through the layouts we must understand some of the basic and important
attributes of layout and views.
|
Attribute
|
Description
|
|
android:id
|
This is the ID which uniquely identifies the view.
|
|
android:layout_width
|
This is the width of the view.
|
|
android:layout_height
|
This is the height of the view
|
|
android:layout_marginTop
|
This is the extra space on the top side of the view.
|
|
android:layout_marginBottom
|
This is the extra space on the bottom side of the view.
|
|
android:layout_marginLeft
|
This is the extra space on the left side of the view.
|
|
android:layout_marginRight
|
This is the extra space on the right side of the view.
|
|
android:layout_gravity
|
This specifies how child Views are positioned.
|
|
android:layout_weight
|
This specifies how much of the extra space in the layout should
be allocated to the View.
|
LinearLayout
A Linear
Layout arranges all its children in vertical or horizontal direction, this
direction is is given by android:orientation
attribute. There are two
possible values for this attrinute , vertical and horizontal.
Lets
discuss each of them separately.
Vertical
Linear Layout
In
vertical layouts children are arranged in vertical direction.
Example:
Create a new layout inside layout folder
with name main.xml
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:layout_marginTop="30dp">
<TextView
android:id="@+id/textView1"
android:layout_gravity="center_horizontal"
android:layout_marginTop="30dp"
android:layout_marginBottom="25dp"
android:textSize="25dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="This Is
Vertical Orientation" />
<Button
android:id="@+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Button 1"
/>
<Button
android:id="@+id/button2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Button 2"
/>
<Button
android:id="@+id/button3"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Button 3"
/>
<Button
android:id="@+id/button4"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Button 4"
/>
</LinearLayout>
Now
inflate this layout main.xml in your
Activity class
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle
savedInstanceState) {
super.onCreate(savedInstanceState);
//
Inflate the layout
setContentView(R.layout.main);
}
}
You can
see all child views(1 textview and 4 buttons) are placed vertically in the
scrren..
