ScrollView android exam

ScrollView

A ScrollView is a special type of FrameLayout in that it allows users to scroll through a list of views that occupy more space than the physical display. The ScrollView can contain only one child view or ViewGroup, which normally is a LinearLayout.
Note: Do not use a ListView together with the ScrollView. The ListView is designed for showing a list of related information and is optimized for dealing with large lists.
The following main.xml content shows a ScrollView containing a LinearLayout, which in turn contains some Button and EditText views:

<?xml version="1.0" encoding="utf-8"?>
<ScrollView
    android:id="@+id/widget54"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    >
    <LinearLayout
        android:layout_width="310px"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        >
        <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"
            />
        <EditText
            android:id="@+id/txt"
            android:layout_width="fill_parent"
            android:layout_height="300px"
            />
        <Button
            android:id="@+id/button4"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Button 4"
            />
        <Button
            android:id="@+id/button5"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Button 5"
            />
    </LinearLayout>
</ScrollView>

Figure 12 shows the ScrollView displaying a scroll bar on the right side of the screen. Users can drag the screen upward to reveal the views located at the bottom of the screen.

Figure 12 Using the ScrollView

FrameLayout android exam

FrameLayout

The FrameLayout is a placeholder on screen that you can use to display a single view. Views that you add to a FrameLayout is always anchored to the top left of the layout. Consider the following content in main.xml:

<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
    android:id="@+id/widget68"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    >
    <FrameLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_x="40px"
        android:layout_y="35px"
        >        
        <ImageView
            android:src = "@drawable/androidlogo"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />
    </FrameLayout>
</AbsoluteLayout>

Here, you have a FrameLayout within an AbsoluteLayout. Within the FrameLayout, you embed an ImageView view. The UI is as shown in Figure 10.
Note: This example assumes that the res/drawable folder has an image named androidlogo.png.

Figure 10 Using FrameLayout

If you add another view (such as a Button view) within the FrameLayout, the view will overlap the previous view (see also Figure 11):

<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
    android:id="@+id/widget68"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    >
    <FrameLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_x="40px"
        android:layout_y="35px"
        >        
        <ImageView
            android:src = "@drawable/androidlogo"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />            
        <Button
            android:layout_width="124px"
            android:layout_height="wrap_content"
            android:text="Print Picture"       
            />
    </FrameLayout>
</AbsoluteLayout>

Figure 11 Overlapping views

You can add multiple views to a FrameLayout, but each will stack on top of the previous one.

RelativeLayout android exam

RelativeLayout

The RelativeLayout lets you specify how child views are positioned relative to each other. Consider the following main.xml file:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    android:id="@+id/RLayout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    >
    <TextView
        android:id="@+id/lblComments"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Comments"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        />
    <EditText
        android:id="@+id/txtComments"
        android:layout_width="fill_parent"
        android:layout_height="170px"
        android:textSize="18sp"
        android:layout_alignLeft="@+id/lblComments"
        android:layout_below="@+id/lblComments"
        android:layout_centerHorizontal="true"
        />
    <Button
        android:id="@+id/btnSave"
        android:layout_width="125px"
        android:layout_height="wrap_content"
        android:text="Save"
        android:layout_below="@+id/txtComments"
        android:layout_alignRight="@+id/txtComments"
        />
    <Button
        android:id="@+id/btnCancel"
        android:layout_width="124px"
        android:layout_height="wrap_content"
        android:text="Cancel"
        android:layout_below="@+id/txtComments"
        android:layout_alignLeft="@+id/txtComments"
        />
</RelativeLayout>

Notice that each view embedded within the RelativeLayout have attributes that allow them to align with another view. These attributes are:

• layout_alignParentTop
• layout_alignParentLeft
• layout_alignLeft
• layout_alignRight
• layout_below
• layout_centerHorizontal

The value for each of these attributes is the ID for the view that you are referencing. The above XML UI creates the screen shown in Figure 9.

Figure 9 Using RelativeLayout to layout views

TableLayout android exam

TableLayout

The TableLayout groups views into rows and columns. You use the <TableRow> element to designate a row in the table. Each row can contain one or more views. Each view you place within a row forms a cell. The width for each column is determined by the largest width of each cell in that column.
Populate main.xml with the following elements and observe the UI as shown in Figure 7.

<?xml version="1.0" encoding="utf-8"?>
<TableLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="fill_parent" 
    android:layout_width="fill_parent"
    android:background="#000044">
    <TableRow> 
        <TextView 
            android:text="User Name:"
            android:width ="120px"
            />
        <EditText 
            android:id="@+id/txtUserName" 
            android:width="200px" />
    </TableRow> 
    <TableRow>
        <TextView 
            android:text="Password:"
            />
        <EditText 
            android:id="@+id/txtPassword" 
            android:password="true" 
            />
    </TableRow>
    <TableRow>
        <TextView />
        <CheckBox android:id="@+id/chkRememberPassword"
            android:layout_width="fill_parent" 
            android:layout_height="wrap_content"
            android:text="Remember Password"
            />   
    </TableRow>
    <TableRow>
        <Button 
            android:id="@+id/buttonSignIn" 
            android:text="Log In" />
    </TableRow>
</TableLayout>

Figure 7 Using the TableLayout

Note that in the above example, there are two columns and four rows in the TableLayout. The cell directly under the Password TextView is populated with an empty element. If you don't do this, the Remember Password checkbox will then appear under the Password TextView, like that shown in Figure 8.

Figure 8 Note the change in the position of the Remember Password view

AbsoluteLayout android exam

AbsoluteLayout

The AbsoluteLayout lets you specify the exact location of its children. Consider the following UI defined in main.xml:

<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    >
    <Button
        android:layout_width="188px"
        android:layout_height="wrap_content"
        android:text="Button"
        android:layout_x="126px"
        android:layout_y="361px"
        />
    <Button
        android:layout_width="113px"
        android:layout_height="wrap_content"
        android:text="Button"
        android:layout_x="12px"
        android:layout_y="361px"
        />
</AbsoluteLayout>

Figure 6 shows the two Button views located at their specified positions using the android_layout_x and android_layout_y attributes.

Figure 6 Views laid out using AbsoluteLayout

Author's Note. You should ideally use AbsoluteLayout when you need to reposition your views when there is a change in the screen rotation.

LinearLayout android exam

LinearLayout

The LinearLayout arranges views in a single column or single row. Child views can either be arranged vertically or horizontally. To see how LinearLayout works, let's modify the main.xml file in the project:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView  
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:text="@string/hello"
        />
</LinearLayout>

In the main.xml file, observe that the root element is <LinearLayout> and it has a <TextView> element contained within it. The <LinearLayout> element controls the order in which the views contained within it appear.
Each View and ViewGroup has a set of common attributes, some of which are shown in Table 1.

Attribute	Description
layout_width	Specifies the width of the View or ViewGroup
layout_height	Specifies the height of the View or ViewGroup
layout_marginTop	Specifies extra space on the top side of the View or ViewGroup
layout_marginBottom	Specifies extra space on the bottom side of the View or ViewGroup
layout_marginLeft	Specifies extra space on the left side of the View or ViewGroup
layout_marginRight	Specifies extra space on the right side of the View or ViewGroup
layout_gravity	Specifies how child Views are positioned
layout_weight	Specifies how much of the extra space in the layout to be allocated to the View
layout_x	Specifies the x-coordinate of the View or ViewGroup
layout_y	Specifies the y-coordinate of the View or ViewGroup

Table 1 Common attributes of views and viewgroups

Note that some of these attributes are only applicable when a View is in certain specific ViewGroup(s). For example, the layout_weight and layout_gravity attributes are only applicable if a View is either in a LinearLayout or TableLayout.
For example, the <TextView> element above has its width filling up the entire width of its parent (which is the screen in this case) 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 (in this case, the text contained within it). If you do not wish to have the <TextView> view occupy the entire row, you can set its layout_width attribute to wrap_content, like this:

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/hello"
    />

This will set the width of the view to be equal to the width of the text contained within it. You can also set the width to an absolute value, like this:

<TextView
    android:layout_width="105px"
    android:layout_height="wrap_content"
    android:text="@string/hello"
    />

In this case, the width is set to 105 pixels wide. Let's modify the main.xml file by adding a <Button> view as shown below:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    >
    <TextView
        android:layout_width="105px"
        android:layout_height="wrap_content"
        android:text="@string/hello"
        />
    <Button
        android:layout_width="100px"
        android:layout_height="wrap_content"
        android:text="Button"
        />
</LinearLayout>