Stack Widget in Flutter

 

Hello everyone. I wanted to write about a widget that I found complicated during my Flutter learning process but is almost essential for creating remarkable interfaces: Stack.

When creating complex user interfaces, it’s really important to combine different widgets together to create flexible and beautiful designs. In this context, the Stack widget is an important tool. The Stack widget is used to place widgets on top of one another, making it ideal for creating rich and layered UIs.

What is a Stack Widget?

Stack is a collection of widgets that contains different widgets stacked on top of each other. These widgets appear at the top of the screen and can be related to each other. For example, a Stack widget can contain an image, text and a button; these widgets can be arranged on top of each other on the screen.

Basic Use of the Stack Widget

The Stack widget is used to place different widgets on top of one another. The basic usage is that the widgets added in a Stack widget overlap in the order they were added.

For example, we can add an image and a text widget to a Stack and place them on top of each other on the screen. The widget added first will appear at the bottom and the widget added last will appear at the top.

Stack(
  children: <Widget>[
    // Widget to appear at bottom
    Container(
      color: Colors.blue,
      width: 200,
      height: 200,
    ),
    // Widget to appear on top
    Positioned(
      top: 50,
      left: 50,
      child: Text(
        'Hello, Flutter',
        style: TextStyle(fontSize: 20),
      ),
    ),
  ],
)

Working with Positioned Widget

In Flutter, the Positioned widget is used to determine the position of widgets in the Stack. This widget is used to place other widgets in the Stack in a specific position. The Positioned widget gives you the flexibility to specify a particular position and size when placing widgets in the Stack.
For example, we can use the Positioned widget to place a Container widget in the top right corner of the Stack:

Stack(
  children: <Widget>[
    Positioned(
      top: 0,
      right: 0,
      child: Container(
        width: 100,
        height: 100,
        color: Colors.red,
      ),
    ),
    // Other widgets can be added here
  ],
)

Another important point to be aware of when using the Positioned widget is that the position and size values must remain within the boundaries of the Stack widget. Otherwise, widgets may overflow from the screen or undesired results may occur.

Stack and Z-Index Management

Z-Index allows a widget to rise above other widgets. The larger the Z-Index value, the higher the widget will appear. We can specify Z-Index values using the Positioned widgets inside the Stack widget.

For example, in the code snippet below, there is an image and some text inside a Stack. However, we want the text to appear above the image. To achieve this, we can use the z-index property of the Positioned widget:

Stack(
  children: <Widget>[
    // Background image
    Image.network(
      'https://example.com/background-image.jpg',
      width: 300,
      height: 300,
      fit: BoxFit.cover,
    ),
    // Text Above
    Positioned(
      top: 50,
      left: 50,
      child: Text(
        'Text Above',
        style: TextStyle(fontSize: 20),
      ),
      // Z-Index determination
      zIndex: 1,
    ),
  ],
)

Considerations and Common Mistakes When Using the Stack Widget

1. Position Calculation Errors: We need to be careful when determining the position of widgets in the stack. If we set the wrong position values, widgets can appear in unwanted places or overlap each other.
2. Z-Index Conflict: Since the Z-Index values of the widgets in the stack determine which widget will be on top of the other, we must carefully determine the Z-Index values; otherwise, widgets may overlap in unwanted ways.
3. Stack Overflow Issues: This topic is not related to the site that we all help :) It makes no sense to use Stack within Stack. Also, adding too many widgets into it can cause widgets to overflow beyond the screen limits or cause errors.
4. Performance Issues: Using too many widgets inside a Stack widget can cause performance issues. Especially when used with animations and complex widgets, performance losses can occur.
5. Missing or Over Positioned Widgets: We use the Positioned widget to determine the position of widgets in the Stack, but adding missing or excessive Positioned widgets can lead to undesirable results. We need to make sure that we have the right number and positioned Positioned widgets for each widget in the stack.
6. Sizing Issues: We need to pay close attention to the size of the widgets in the Stack. Especially, if the sizes of the widgets in the Stack are different from each other, widgets can overflow from the screen or unexpected errors can be received.
7. Hierarchy of Widgets: The hierarchy of widgets in the Stack is also very important. In some cases, if the relationship between multiple widgets in the Stack is unclear, it can lead to unexpected results. Therefore, we should carefully plan the hierarchical relationship of widgets.

The Stack widget that we will create by paying attention to these points is a very important tool for us to create more robust and stable user interfaces.

I hope my article was useful for everyone.

Have a good work.

Selin.