User Interface In Android Applications

Pradip Pandey
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Overview

I hope, you got a chance to read some useful articles to start programming in Android Applications. The useful links are given below:

Introduction

You know about an Activity and how its life cycle and activity is a means by which users interact with the Application. However, an activity by itself does not have a presence on the screen. An activity displays the user interface of your Application, which may contain some widgets such as buttons, labels, textboxes etc. Basically, it is defined in the XML file, generally called the main.xml file, located in the res/layout folder of your project.

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" tools:context=".MainActivity">
<Button android:id="@+id/buttondisplaynotification"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:text="Show Notification"
android:onClick="onClickShowNotification"
/>
</LinearLayout>

During the runtime, it is loaded in the onCreate() method handler in the Activity class, using the setContentView() method.

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}

During the compilation, each element in XML file is compiled into an equivalent Android GUI class with the attributes, represented by the methods.

In this article, you will learn about some widgets like Views, ViewGroups, LinearLayout, AbsoluteLayout, TableLayout, RelativeLayout, FrameLayout, ScrollView etc.

An activity contains Views and Viewgroups. A View is a widget, which has an appearance on the screen. E.g buttons, labels, textboxes etc. It is derived from the base class android.view.View.

In ViewGroup, one or more Views can be grouped together. A ViewGroup provides the layout, in which you can set the order of the appearance and sequence of the Views. Some examples of ViewGroups are LinearLayout and FrameLayout. It is derived from the base class android.view.ViewGroup.

Android supports the following ViewGroups.

LinearLayout
AbsoluteLayout
TableLayout
RelativeLayout
FrameLayout
ScrollView

Let us see all these one by one.

LinearLayout

The LinearLayout arranges a View in a single column or a single row. Thus, child Views can be arranged either vertically or horizontally. If you want to see how LinearLayout works, consider the following elements, typically contained in the manin.xml file.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" tools:context=".MainActivity">
<Button android:id="@+id/buttondisplaynotification"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:text="Show Notification"
android:onClick="onClickShowNotification"
/>
</LinearLayout>

In the main.xml file, you can see that the root element is <LinearLayout> and it has a <Button> element, contained within it. The <LinearLayout> element controls the order, in which the views contained within it appears. The table, given below, shows the common attributes, used in the View and ViewGroups:

ATTRIBUTE	DESCRIPTION
Lauout_width	It specifies the width of the View and ViewGroup.
Layout_height	It specifies the height of the View and ViewGroup.
Layout_marginTop	It specifies the extra space on the top side of the View or Viewgroup
Layout_marginBotton	It specifies the extra space on the bottom side of the View or Viewgroup
Layout_marginLeft	It specifies the extra space on the left side of the View or Viewgroup.
Layout_marginRight	It specifies the extra space on the right side of the View or Viewgroup
Layout_gravity	It specifies, how child Views are positioned.
Layout_weight	It specifies, how much extra space in the layout should be allocated to the View.
Layout_x	It is x-coordinate of the view or Viewgroup.
Layout_y	It is y-coordinate of the view or Viewgroup.

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Check it for layout!!"
/>

Suppose, in the above <TextView> element, the width fills the entire width of its parent, using the fill_parent constant. Its height is indicated by the wrap_content constant, which means that its height is the height of its content. If you don’t want the <TextView> View to occupy the entire row, you can set its layout width attribute to wrap_content.

Now, make some changes in the properties of the element in the same file as:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" tools:context=".MainActivity">
<TextView
android:layout_width="100dp"
android:layout_height="wrap_content"
android:text="See User Interface Effect by changing dp to px"/>
<Button android:id="@+id/buttondisplaynotification"
android:layout_width="120dp"
android:layout_height="fill_parent"
android:text="Show Notification"
android:onClick="onClickShowNotification"
/>
</LinearLayout>

In the code, given above, set the width of both the TextView and Button Views to an absolute value. The width is 100dp (dp is referred as density-independent pixels) and Button is 120dp.

The screenshot, mentioned above is the screen of Nexus 4. It has 4.7 inches screen (diagonally), with a screen width of 2.08 inches.

We can see in the screenshot, given above, what Views looks like on the different screens with different pixel density. Thus, it is important to understand, how Android recognizes the screens of varying sizes and density.

Android defines and recognizes four types of screen densities.

Low Density(lDPI)
Medium Density(MDPI)
High Density(HDPI)
Extra High Density(XHDPI)

Above image comes into one of the densities, defined in the preceding list. E.g. Nexus 4 is regarded as a XHDPI device, as its pixel density is closest to 240 dpi. Unit dp ensures that the Views are displayed in the right proportion, regardless of the screen density. Basically, Android automatically scales the size of the view, depending on the density of the screen. E.g. A Button is displayed on 120 dpi screen, its width would be 90 pixels because a 120 dpi screen is treated, just like a 100 dpi screen. If it is displayed on a 165 dpi screen, its width would be 124 pixels.

Below is the formula to convert dp to px.

Px = dp * (dpi/160), where dpi is either 120, 160, 240 or 320.

Px = 120 * (120/160) = 90

Px = 165 * (120/160) = 124 approx.

We see that one dp is equivalent to one px.

Now, we will see about the changes, when the size is defined in pixels(px) instead of dp.

<TextView
android:layout_width="100px"
android:layout_height="wrap_content"
android:text="See User Interface Effect by changing dp to px"/>
<Button android:id="@+id/buttondisplaynotification"
android:layout_width="120px"
android:layout_height="fill_parent"
android:text="Show Notification"
android:onClick="onClickShowNotification"
/>

Run the app and the result is displayed below:

It shows, that if you use pixels for the View sizes, the Views will appear smaller on a device with a high dpi screen, compared to one with a lower dpi.

In the example, mentioned above, orientation of the layout is set as vertical.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" tools:context=".MainActivity">

The default orientation layout is horizontal. If you remove this attribute, the Views will look like as given below:

In LinearLayout, we can use layout_weight and layout_gravity attributes to the View, contained within it. We do some changes in the main.xml file.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:layout_width="100px"
android:layout_height="wrap_content"
android:text="See User Interface Effect by changing dp to px"/>
<Button android:id="@+id/buttondisplaynotification"
android:layout_width="120px"
android:layout_height="fill_parent"
android:text="Show Notification"
android:onClick="onClickShowNotification"
android:layout_weight="1"
android:layout_gravity="center"
/>
</LinearLayout>

Run the app and see the difference, given below:

Now, we change the orientation of LinearLayout to horizontal from vertical, given below:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal"
tools:context=".MainActivity">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="See User Interface Effect by changing dp to px"
android:layout_gravity="left"
android:layout_weight="1"
/>
<Button android:id="@+id/buttondisplaynotification"
android:layout_width="0dp"
android:layout_height="fill_parent"
android:text="Show Notification"
android:onClick="onClickShowNotification"
android:layout_weight="2"
android:layout_gravity="center"
/>
</LinearLayout>

Afterwards, we need to change the width of each view to 0 dp and it displays the screenshot, given below:

Absolute Layout

It enables us to specify the exact location of its children. Make some changes in main.xml file.

<AbsoluteLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity">
<TextView
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="See user interface effect by changing to absolute layout"
android:layout_x="50px"
android:layout_y="100px"
/>
<Button android:id="@+id/buttondisplaynotification"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:text="Show Notification"
android:onClick="onClickShowNotification"
android:layout_x="150px"
android:layout_y="180px"
/>
</AbsoluteLayout>

Run the app and result looks like the screenshot, given below:

In the result, given above, the elements are the specified positions, using the android:layout_x and android:layout_y attributes. Android will not support them in their future versions, so we should avoid using this layout.

Table Layout

It groups the Views into rows and columns. <TableRow> element is used to design a row in the table. Each row can contain one or more Views. Each View is placed within a row to form a cell. The width of each column is determined by the largest width of each cell in the column. Let’s make some changes in the file main.xml.

<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity">
<TableRow>
<TextView
android:text="Enter Email"
android:width="120dp"
/>
<EditText
android:id="@+id/txtemail"
android:width="150dp"
/>
</TableRow>
<TableRow>
<TextView
android:text="Enter Password"
android:width="120dp"
/>
<EditText
android:id="@+id/txtpassword"
android:width="150dp"
android:password="true"
/>
</TableRow>
<TableRow>
<Button
android:text="Login"
android:id="@+id/buttonLogin"
/>
</TableRow>
</TableLayout>

Run the app and the result looks like the screenshot, given below:

In the preceding code, there are two columns and three rows in the TableLayout. Make some changes to one more element as Remember Me in checkbox.

<TableRow>
<TextView />
<CheckBox
android:text="Remember Me"
android:id="@+id/chkboxrememberme"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
</TableRow>
<TableRow>
<TextView />
<Button
android:text="Login"
android:id="@+id/buttonLogin"
/>
</TableRow>

Run the app and see the result, given below:

In the preceding code, the cell is populated, directly under the Password TextView with a <TextView/> empty element. It will display under the PasswordTextView, if we don’t do this.

Relative Layout

This layout enables us to specify, how child Views are positioned, relative to each other. Make some changes in the main.xml file as:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Message"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:id="@+id/txtnotifications"
/>
<EditText
android:layout_width="fill_parent"
android:layout_height="150px"
android:layout_alignLeft="@+id/txtnotifications"
android:layout_below="@+id/txtnotifications"
android:layout_centerHorizontal="true"
android:id="@+id/editnotifications"
/>
<Button
android:layout_width="180px"
android:layout_height="wrap_content"
android:text="Save"
android:layout_below="@id/editnotifications"
android:layout_alignLeft="@id/editnotifications"
android:id="@+id/buttonsave"
/>
<Button
android:layout_width="160px"
android:layout_height="wrap_content"
android:text="Cancel"
android:layout_below="@id/editnotifications"
android:layout_alignRight="@id/editnotifications"
android:id="@+id/buttoncancel"
/>
</RelativeLayout>

Run the app and see the result, given in the image, below:

In the image, given above, each View embedded within the RelativeLayout has attributes that enable it to align with another View. These attributes are:

layout_alignParentTop
layout_alignParentLeft
layout_alignLeft
layout_below
layout_centerHorizontal

Frame Layout

This layout is a placeholder on the screen, which we can use to display a single View. It is always anchored to the top left of the layout, when we add a FrameLayout. Thus, let’s do some changes in the file main.xml.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Welcome you at Frame Layout"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:id="@+id/txtnotifications"
/>
<FrameLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/txtnotifications"
android:layout_below="@+id/txtnotifications"
android:layout_centerHorizontal="true"
>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="100px"
android:layout_marginTop="20px"
android:src="@drawable/ic_launcher"
/>
</FrameLayout>
</RelativeLayout>

Run the app and see the result in the image, given below:

In the preceding code, we have FrameLayout within RelativeLayout and have embedded an ImageView within it. Now, add another view within the FrameLayout, the view will overlap the previous view.

<FrameLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/txtnotifications"
android:layout_below="@+id/txtnotifications"
android:layout_centerHorizontal="true"
>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="100px"
android:layout_marginTop="20px"
android:src="@drawable/ic_launcher"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Show Image"
/>
</FrameLayout>

Run the app and see the result, given below in the image:

Scroll View

This layout is a special type of FrameLayout and enables the users to scroll through a list of Views, which can occupy more space than the physical display. It can contain only one child view or view group, which is normally a LinearLayout. Let’s do some changes in the main.xml file.

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:focusable="true"
android:focusableInTouchMode="true"
>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Display 1"
android:id="@+id/buttondisplay1"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Display 2"
android:id="@+id/buttondisplay2"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Display 3"
android:id="@+id/buttondisplay3"
/>
<EditText
android:layout_width="fill_parent"
android:layout_height="400dp"
android:id="@+id/textbox1"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Display 4"
android:id="@+id/buttondisplay4"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Display 5"
android:id="@+id/buttondisplay5"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Display 6"
android:id="@+id/buttondisplay6"
/>
</LinearLayout>
</ScrollView>

Run the app and see the result, as the image, given below:

The ExitText automatically gets the focus. It fills up the entire activity. Next, add two attributes to the <LinearLayout> element.

android:focusable="true"
android:focusableInTouchMode="true"

After adding these attributes, we are now able to view the buttons and scroll through the list of Views.

Conclusion

In this article, you learned about various types of layout (LinearLayout, AbsoluteLayout, TableLayout, Relative Layout, Frame Layout and Scroll View). In the next article, I will explain about an orientation, anchoring, resizing and repositioning of the Views. If you have any questions or comments, post it on C# Corner comments section.

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