Android Layouts & Attributes

Android Layouts

• In Android, Layouts are fundamental building blocks of the user interface.
• They are containers that dictate the visual structure and arrangement of the UI components (like TextView, Button, ImageView, etc.) placed within them.
• In Android development, layouts define the structure and arrangement of UI components (such as buttons, text views, images, etc.) on the screen.
• Layouts are essentially containers that hold and organize these UI elements.
• Layouts are subclasses of the ViewGroup class.
• Android layouts are essential containers that hold and organize UI elements. It is used for designing the user interface of Android applications.
• They define how UI elements are arranged and displayed on the screen.
• A typical layout defines the visual structure for an Android user interface.
• It can be created either at run time using View/ ViewGroup objects, or we can declare our layout using a simple XML file, which is located in the res/layout folder of our project.
• Android provides several types of layouts, each serving a specific purpose or offering different ways to position and size UI components.

Android Layout Types

• Several types of Layouts will be used in almost all Android applications to provide a different view, look, and feel. These are:-
  • Linear Layout
    • LinearLayout is a view group that aligns or arranges all its child elements in a single row (horizontal) or column (vertical).
    • This layout is ideal for simple, linear arrangements of UI components.
    • This layout has two attributes : android:orientation=”horizontal” for a row and android:orientation=”vertical” for a column.
    • This is one of the simplest and most commonly used layouts.
    • When to Use:
      • For simple lists of items (e.g., a settings screen).
      • For forms with labels and input fields stacked vertically.
    • Advantages:
      • Very simple and easy to understand.
      • Predictable and great for simple, linear UIs.
    • Disadvantages:
      • Can lead to deep nesting to create complex UIs (e.g., LinearLayout inside another LinearLayout), which is very bad for performance.
  • Relative Layout
    • A RelativeLayout positions its child elements relative to each other or to the parent container.
    • RelativeLayout is a view group that displays child views in relative positions.
    • This is useful when we need flexible positioning of UI elements without nesting too many layouts.
    • Advantages:
      • This layout allows for flat view hierarchies.
      • This layout is more flexible than LinearLayout.
    • Disadvantages:
      • It can become very difficult to manage and debug as the number of rules increases.
      • It is less performant than ConstraintLayout.
    • The code attributes of this layout are  android:layout_alignParentTop, android:layout_alignParentBottom, etc. : Aligns a view to the edges of the parent.
    • The code attributes of this layout are android:layout_toRightOf, android:layout_below, etc.: Positions a view relative to another view.
  • Constraint Layout
    • This layout was introduced in Android Studio 2.2.
    • This layout is a modern & recommended layout.
    • This is the most powerful and flexible layout in the Android toolkit.
    • It is now the default layout for new projects in Android Studio and is highly recommended for building complex, responsive UIs.
    • In this layout, each view is positioned by creating constraints to other views or the parent layout. A constraint defines a relationship like “this view’s left side should align with that view’s right side” or “this view should be centered horizontally in the parent.”
    • Instead of nesting layouts, this layout helps in creating a flat view hierarchy by defining relationships, or constraints, between different UI elements and their parent container.
    • This layout allows for creating complex layouts with flat view hierarchies (minimal nesting).
    • This layout uses constraints to position and size widgets relative to the parent or other widgets.
    • In other words, this is a flexible layout that allows us to create complex layouts by setting constraints between views, offering flexibility and responsiveness with a flat view hierarchy.
    • Android Constraint Layout is used to define a layout by assigning constraints for every child view/widget relative to other views present.
    • The constraint applied in this layout provides more control over the positioning of UI elements.
    • A Constraint Layout is similar to a relative layout, but with more power.
    • Constraint Layout aims to improve the performance of applications by removing the nested views with a flat and flexible design.
    • This layout supports chains, guidelines, and barriers for advanced layouts.
    • This layout is optimized for performance and reduces overdraw (compared to nested layouts).
    • The common key attributes of Constraint layout are –
      
      – app:layout_constraintTop_toTopOf: Constrains the top of this view to the top of another view/parent.
      – app:layout_constraintStart_toEndOf: Constrains the start of this view to the end of another view.
      – app:layout_constraintDimensionRatio: Forces a specific aspect ratio (e.g., 16:9).
      – app:layout_constraintHorizontal_bias: Positions a view along the horizontal axis when it has constraints on both sides.
      – Chains: To distribute a group of views horizontally or vertically (packed, spread, spread_inside).
      – Guidelines, Barriers, Groups: Helper objects for more complex alignments.
    • When to Use Constraint Layout:
      • Used for almost any UI, from simple to highly complex.
      • When we need to create responsive layouts that adapt to different screen sizes.
      • When we want to avoid deep, nested layouts to improve performance.
    • Advantages of Constraint Layout:
      • Flat Hierarchy: It can lead to significantly better performance than nested layouts.
      • Highly Flexible: It can create virtually any UI design.
      • Excellent Tooling: Android Studio has a powerful visual “Layout Editor” for creating constraints.
    • Disadvantages of Constraint Layout:
      • The XML can be verbose and hard to read by hand initially.
      • This layout has a slightly steeper learning curve than simpler layouts like Linear Layout.  

• • Absolute Layout
    • This is a deprecated layout in Android. It was part of the early Android framework (API Level 3 (Android 1.5)) but was quickly found to be a very poor approach for building user interfaces. It is no longer recommended for use because it doesn’t adapt well to different screen sizes, resolutions, or orientations. While deprecated, it might still be used in legacy projects or very specific scenarios where pixel-perfect placement is required (e.g., custom drawing apps or games).
    • Absolute Layout enables the specification of the exact location of its child views.
    • This layout manager in Android allows developers to position their user interface (UI) elements precisely by specifying exact x and y coordinates, i.e., using this layout, we can place each UI component at a specific location on the screen, measured in pixels from the top-left corner of the parent container. 
    • We have full control over where each UI element is placed on the screen.
    • It is simple for small, fixed-size screens or prototypes; it can be straightforward to use.
    • This layout is the most rigid of all layouts, i.e., it creates UIs that are completely inflexible.
    • The primary attributes used in this layout are:
      • android:layout_x: The exact horizontal position.
      • android:layout_y: The exact vertical position.
    • This layout, built with hardcoded coordinates, will only look correct on the exact screen size and density devices it was designed for. On any other screen or device, the UI will be broken.
    • Hardcoding positions makes the layout difficult to maintain and update, especially when designing for multiple devices.
    • It cannot adapt to screen orientation changes (portrait vs. landscape). The coordinates remain the same, leading to a jumbled UI.
  • Frame Layout
    • This is the simplest layout container.
    • This layout is designed to stack its children one on top of the other, like a stack of papers. The last child added is on top of the stack.
    • The Frame Layout is a placeholder on the screen that is used to display more than one view as a single view.
    • It is useful for overlaying views, like adding a loading spinner on top of an image.
    • This layout places child views on top of each other, which is often used for simple container layouts.
    • Here, all child views are pinned to the top-left corner by default.
    • When to Use:
      • To overlay views (e.g., a play button on top of a video thumbnail).
      • As a container for a single child, often used for Fragments.
    • Advantages:
      • It is very lightweight and efficient for its specific purpose.
    • Disadvantages:
      • It is not suitable for arranging multiple non-overlapping items.
  • List View/ScrollView
    • ListView is a view group that displays a list of scrollable items.
    • It is a special type of layout that allows vertical scrolling of child views.
    • It is typically used for longer content that doesn’t fit on the screen.
  • Grid Layout View
    • This layout organizes views in a grid format, allowing us to specify row and column positions.
    • This layout is suitable for creating a grid-like structure for items (e.g., in a photo gallery).
    • GridView is a ViewGroup that displays items in a two-dimensional, scrollable grid.
  • Table Layout
    • This layout organizes views into groups as rows and columns, similar to an HTML table.
    • This layout is useful for forms and structured data.

Android Layouts Attributes

• In Android development, layout attributes are used to define the size, position, alignment, margins, padding, and other properties of UI components within a layout.
• These attributes are specified in XML files when designing the user interface (UI).
• Each Android layout has a set of attributes that define the visual properties of that layout.
• There are a few common attributes among all the layouts, and there are other attributes that are specific to that layout.
• The common Layout attributes are as follows –
  • android: id
    • This is the ID that uniquely identifies the view/UI element that is used in Java/Kotlin coding to call or represent it.
    • It is a unique identifier for the view and is crucial for referencing the view in our Kotlin/Java code or from other views in the XML layout.
    • For example – android:id=”@+id/username”.
  • android: orientation
    • Applicable mainly in Linear Layout view.
    • The android: orientation attribute is used in Android layouts, specifically in the LinearLayout class, to define the direction in which child views are laid out.
    • The LinearLayout can arrange its children in a vertical column or a horizontal row using android:orientation=”vertical”  and android:orientation=”horizontal” respectively.
    • When android:orientation=”vertical” is set, the child views of the LinearLayout are arranged in a vertical column. Each child is stacked below the previous one.
    • When android:orientation=”horizontal” is set, the child views of the LinearLayout are arranged in a row. Each child is arranged side by side in a row.

  • android:layout_width

    • This attribute specifies the width of the view/layout.
    • Android:layout_width=wrap_content tells about the view wants to be just big enough to enclose its content, or occupying the size itself to the dimensions required by its content, or the view is only as wide as its content. The view will take up just enough space to fit its content.
    • android:layout_width=fill_parent tells us about the view becoming as big as its parent view.
    • android:layout_width=match_parent tells us the view wants to be as big as its parent container, or for the view to take up as much space as its parent View allows, or the view takes up all available space. This value is used when we want the view to expand to fill the available space of its parent container. The View will stretch to the width (or height) of the parent View, covering all available space. match_parent is often used for responsive design, ensuring that the View adapts to different screen sizes and orientations.
    • android:layout_width=200dp tells us about the customized view to take the given specific dimensions.
  • android:layout_height
    • This attribute represents the height of the layout/view.
    • It uses the same values as layout_width.
  • android: margin
    • The margin attribute is used to create space around and between child views, ensuring a visually appealing layout.
    • It sets the outer space around the view.
    • A single value of margin applies the same margin to all sides.
    • Margin includes –
      • android:layout_marginTop
        • This attribute represents the extra space on the top side of the layout.
      • android:layout_marginBottom
        • This attribute represents the extra space on the bottom side of the layout.
      • android:layout_marginLeft
        • This attribute represents the extra space on the left side of the layout.
      • android:layout_marginRight
        • This attribute represents the extra space on the right side of the layout.
  • android: padding
    • This attribute sets the inner space between the view’s content and its border.
    • It is similar to Android margins.
    • It can also include:-
      • paddingTop, paddingBottom, paddingLeft, and paddingRight.
      • android:padding-left
        • This attribute represents the left padding filled for the layout.
      • android:padding-right
        • This attribute represents the right padding filled for the layout.
      • android:paddingTop
        • This attribute represents the top padding filled for the layout.
      • android:padding-bottom
        • This attribute represents the bottom padding filled for the layout.
  • android: gravity
    • It aligns/arranges the content within the view.
    • This attribute is useful in layouts like FrameLayout and LinearLayout.
    • The common values of layout_gravity are:- center, left, right, top, bottom.
  • android:layout_gravity
    • This attribute specifies how a child’s view should be positioned within its parent (e.g., in FrameLayout or LinearLayout).
    • This attribute represents how child Views are positioned either horizontally or vertically.
  • android:layout_weight
    • This specifies how much of the extra space in the layout should be allocated to the View.
    • This attribute is used in LinearLayout to allocate space proportionally among child views.
    • A view with a higher weight will take up more space than a view with a lower weight.
  • android:layout_x
    • This specifies the x-coordinate of the layout.
  • android:layout_y
    • This specifies the y-coordinate of the layout.
  • android: background(for Color/Image)

    • The android: background attribute in Android development is used to specify a background for a View. This background can be a color, a drawable resource/image, or a gradient.
    • We can set a solid color as the background of a View. This color can be defined in the colors.xml resource file or directly in the layout XML file.

(I) For Color

<resources> <color name=“color1”>#FF5722</color> </resources>

• • android: hint
    • The android: hint attribute in Android is used to specify a hint for a text input field, such as an EditText.
    • This hint is a text that is displayed inside the text field when it is empty, guiding the user on what kind of input is expected.
    • We can enhance the usability and user experience of our Android application by providing clear guidance on the expected input using Android: hint.
    • It is similar to a Placeholder in HTML. 

• • • <EditText
      • android:layout_width=“match_parent”
      • android:layout_height=“wrap_content”
      • android:hint=“Enter your email” />

• • • <EditText
      • android:layout_width=“match_parent”
      • android:layout_height=“wrap_content”
      • android:hint=“Enter your password”
      • android:inputType=“textPassword” /> 
    • We can change the hint text color using the android:textColorHint attribute.

android:textColorHint=“#FF5722”    directly in XML file  OR

android:textColorHint=“@color/color2”  from Color resource file.

• • • To apply a custom style to the hint text, use a style in your styles.xml file.

<!– res/values/styles.xml –>

• • • • To use/apply the above style to our EditText-
      •  
      • <EditText
        • android:layout_width=“match_parent”
        • android:layout_height=“wrap_content”
        • android:hint=“Enter your name”
        • style=“@style/CustomHintTextStyle” />
  • android: onClick:
    • It specifies the method to be called when the view is clicked (e.g., android:onClick=”submitForm”).
  • android: src:
    • It is used to set the image for the ImageView by selecting a source of the image.
  • android: scaleType:
    • It defines how the image should be scaled/appear within the ImageView.
    • Common values are:

center, centerCrop, fitCenter, fitXY.

• • android:visibility:
    • It defines the visibility state of a view.
    • The values are:
      • visible: This makes the view visible.
      • invisible: This makes the view invisible but still takes up space.
      • gone: This hides the view and does not take up space.
  • Text Specific Attributes:
    • android: text – Sets the text content for views like TextView or Button.
    • android:textSize – Specifies the size of the text (e.g., 16sp).
    • android:textColor – Sets the color of the text.
    • android:textStyle – Defines the style of the text, such as bold, italic, or normal.
    • android:fontFamily – Sets the font family for the text.
    • android:ellipsize – Truncates the text with an ellipsis (…) if it is too long for the available space.
    • android:maxLines – Limits the number of lines a text view can display.
    • android:textAllCaps – Converts all text to uppercase (true / false).
    • android: letterSpacing – Adjusts space between letters.
    • android:lineSpacingExtra – Adds extra space between lines.
    • android:lineSpacingMultiplier – Multiplies default line spacing.
    • android:shadowColor – Adds a text shadow color.
  • For Example:

Units Used in Android Layouts Attributes

• dp (Density-independent Pixels):
  • In Android Studio, the dp unit is used in layout design to specify the size, margin, padding, and position of UI elements (such as views, buttons, text, etc.) in XML layout files.
  • This unit is used to define the object in fixed-size form when we want the View to have a specific dimension regardless of its content or parent size.
  • dp ensures that UI elements appear at the same physical size on different screen densities and resolutions, providing a consistent user experience across various Android devices.
  • dp is used in –
    • Width and height of views (e.g., android:layout_width="100dp")
    • Margins and paddings (e.g., android:layout_margin="16dp", android:padding="8dp")
    • Elevation, radius, and other size-related attributes
• sp ( Scale-independent Pixels):
  • sp units scale according to both the screen density and the user’s font size preference (accessibility settings).
  • This ensures that text remains readable for users who increase or decrease system font size for accessibility.
  • This unit is used for Text size for TextView, EditText, Button, etc., for example: android:textSize="18sp"
• pt ( Points, which is 1/72 of an inch):
• px( Pixels):
• mm ( Millimeters):
• in (inches):