Understanding Child Views in iOS Development
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As an iOS developer, controlling the size and layout of child views can be a challenging task. In this article, we will delve into the world of child views, exploring how to control their size and layout, and provide practical examples to illustrate our points.
What are Child Views?
In iOS development, a child view is a view that is embedded within another view, known as the master view. The child view can be a custom view or a built-in view, such as a UITableView or UIView. Child views are used to organize complex user interfaces into manageable sections.
Creating and Adding Child Views
To create and add child views, we need to understand how to initialize and configure them properly. In the provided code example, we see that two child views, MasterViewController and DetailViewController, are created and added as subviews to the master view.
// Create child views
self.masterViewController = [[MasterViewController alloc] initWithNibName:nil bundle:nil];
self.detailViewController = [[DetailViewController alloc] initWithNibName:nil bundle:nil];
// Add child views to master view
[self.view addSubview:self.masterViewController.view];
[self.view.addSubview:self.detailViewController.view];
Controlling the Size and Layout of Child Views
To control the size and layout of child views, we need to set their frames programmatically. The frame represents the size and position of a view on the screen.
// Set frame for master view
self.masterViewController.view.frame = CGRectMake(0, 0, 100, 100);
// Set frame for detail view
self.detailViewController.view.frame = CGRectMake(100, 100, 200, 200);
Understanding Auto Layout
Auto layout is a feature in iOS that allows us to create complex user interfaces without writing manual code. When we set the frames of child views programmatically, they may not behave as expected due to auto layout constraints.
To control the size and layout of child views effectively, we need to understand how auto layout works. Here’s a brief overview:
- Constraints: Constraints are rules that define the relationship between two or more views.
- Pinning: Pinning refers to setting the position or size of a view relative to another view.
- Space Between: Space between constraints allows us to create space between two or more views.
Setting Frames with Auto Layout
When using auto layout, we need to set frames for child views in a way that respects their constraints. Here’s an example:
// Create child views with auto layout constraints
self.masterViewController = [[MasterViewController alloc] initWithNibName:nil bundle:nil];
self.detailViewController = [[DetailViewController alloc] initWithNibName:nil bundle:nil];
// Set frame for master view with pinning and space between constraints
self.masterViewController.view.frame = CGRectMake(0, 0, 100, 100);
self.masterViewController.view.translatesAutoresizingMaskIntoConstraints = NO;
NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:self.masterViewController.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *leadingConstraint = [NSLayoutConstraint constraintWithItem:self.masterViewController.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *trailingConstraint = [NSLayoutConstraint constraintWithItem:self.masterViewController.view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:-100];
NSLayoutConstraint *bottomConstraint = [NSLayoutConstraint constraintWithItem:self.masterViewController.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
[self.masterViewController.view addConstraints:@[topConstraint, leadingConstraint, trailingConstraint, bottomConstraint]];
// Set frame for detail view with pinning and space between constraints
self.detailViewController.view.frame = CGRectMake(100, 100, 200, 200);
self.detailViewController.view.translatesAutoresizingMaskIntoConstraints = NO;
NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:self.detailViewController.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *leadingConstraint = [NSLayoutConstraint constraintWithItem:self.detailViewController.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:100];
NSLayoutConstraint *trailingConstraint = [NSLayoutConstraint constraintWithItem:self.detailViewController.view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:-200];
NSLayoutConstraint *bottomConstraint = [NSLayoutConstraint constraintWithItem:self.detailViewController.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
[self.detailViewController.view addConstraints:@[topConstraint, leadingConstraint, trailingConstraint, bottomConstraint]];
Conclusion
Controlling the size and layout of child views is a crucial aspect of iOS development. By understanding how to create and configure child views effectively, we can build complex user interfaces with ease. This article has provided an overview of child views, auto layout constraints, and how to set frames for child views using both manual and auto layout approaches.
Example Use Case
Here’s a complete example project that demonstrates the concepts discussed in this article:
iOS Project Structure
iOSProject/
ViewController.swift
MasterViewController.swift
DetailViewController.swift
Main.storyboard
Main.storyboard
Create two view controllers: MasterViewController and DetailViewController. Set their frames programmatically using auto layout constraints.
// Create two view controllers with auto layout constraints
let masterVC = MasterViewController()
let detailVC = DetailViewController()
masterVC.view.translatesAutoresizingMaskIntoConstraints = false
detailVC.view.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(masterVC.view)
view.addSubview(detailVC.view)
NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *leadingConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *trailingConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:-100];
NSLayoutConstraint *bottomConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *topConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:100];
NSLayoutConstraint *leadingConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:100];
NSLayoutConstraint *trailingConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:-200];
NSLayoutConstraint *bottomConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
view.addConstraints:@[topConstraint, leadingConstraint, trailingConstraint, bottomConstraint];
view.addConstraints:@[topConstraintDetail, leadingConstraintDetail, trailingConstraintDetail, bottomConstraintDetail]];
ViewController.swift
Create a ViewController that embeds the two view controllers.
// Create two view controllers and add them to view controller
let masterVC = MasterViewController()
let detailVC = DetailViewController()
view.addSubview(masterVC.view)
view.addSubview(detailVC.view)
NSLayoutConstraint *topConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *leadingConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *trailingConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:-100];
NSLayoutConstraint *bottomConstraint = [NSLayoutConstraint constraintWithItem:masterVC.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
NSLayoutConstraint *topConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:100];
NSLayoutConstraint *leadingConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:100];
NSLayoutConstraint *trailingConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:-200];
NSLayoutConstraint *bottomConstraintDetail = [NSLayoutConstraint constraintWithItem:detailVC.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];
view.addConstraints:@[topConstraint, leadingConstraint, trailingConstraint, bottomConstraint];
view.addConstraints:@[topConstraintDetail, leadingConstraintDetail, trailingConstraintDetail, bottomConstraintDetail]];
Run the app to see the two view controllers embedded in a single ViewController with auto layout constraints.
Last modified on 2024-02-15