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ConstraintLayout
Nicolas Roard
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What is it
• Expressive Layout Manager
• Flat Layouts
• Deep integration with Android Studio + Layout Editor
• Unbundled Library
• Compatible with 99% of devices
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Once upon a time
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The Tetris Model
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The Tetris Model
• Relatively easy at first
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The Tetris Model
• Relatively easy at first
• Can get very complex very quickly
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The Tetris Model
• Change is hard
• Impose limits for animation / transitions
• Not conductive to a great design tool experience
• Performance can become an issue
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Layout
!=
Views
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Flat Layouts
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Flat Layouts
• Layout definition is not mixed with the view hierarchy
• Easy to manipulate in a graphical editor
• Easy to change
• Animation friendly
• Keep layout computation in a single place
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$ANDROID_HOME/platform-tools/systrace/systrace.py
—time=10 -o ~/trace.html gfx view res
CL 1.0.2,
Nexus 5X
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Expressivity
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Solver
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Simplex
• Linear Programming
• Invented by Georges Dantzig in 1947
• Large, empty matrices representing the
equations
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Example
Minimize
Constrained by
Z x y z s t =
Basic Feasible Solution (BFS)
Matrix representation
(plus slack variables s & t)
Pivot on z, row 2
BFS
Objective row
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Cassowary
• https://constraints.cs.washington.edu/cassowary/
• Constraints for User Interface Applications
• Alan Borning, Kim Marriott, Peter Stuckey, and Yi Xiao, Solving
Linear Arithmetic, Proceedings of the 1997 ACM Symposium on
User Interface Software and Technology, October 1997, pages
87-96.
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Cassowary
• Incremental resolution and construction of the system
• Handles positive and negative variables
• Goal function and error representation
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Pros / Cons
• Very flexible, can represent any type of layout situation
• But “relatively” heavy computation compared to simple layouts
• Can be more memory intensive
• Specifying layout via equations?…
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ConstraintLayout solver
• Pure java
• Represents the system matrix as rows of sparse arrays
• Memory Efficient
• Efficient incremental construction
• Has to have good performances on both Dalvik and Art
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Constraints Model
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Constraints Model
• Simple model — relative positioning, centering
• No Equations exposed
• Evolving (bias, new dimension constraints, etc.)
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Constraints Model
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Constraints Model
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Constraints Model
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Constraints Model
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Constraint Layout
Solver
Constraints Model
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Constraint Layout
Solver
Constraints Model
Optimizer
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Optimizer
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Optimizer
• Constraints which can be resolved unambiguously
• app:layout_optimizationLevel=“none|all|basic|chains”
• multiple steps:
• wrap content computation
• direct resolution of simple dependency
• chains on parent
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Optimizer
• match_constraint is more costly, as we need to remeasure
• wrap_content, fixed dimension are cheap on a widget (end up as a
value in the solver)
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Optimizer - wrap content
• If widgets contain match_constraint, no optimizations:
• if ratio is specified
• if percent is specified (for dimension, guideline)
• if wrap_content is specified in the other dimension
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Optimizer - Direct resolution
• Only if the container is not in wrap_content
• Only for widgets that are not match_constraints
• Will resolve as much as it can before handing the system
to the full solver
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Optimizer - Chains
• Only for chains that are connected to the container (stable
endpoints)
• Only for widgets in a chain that are not match_constraints / ratio
• Right now, only for chains in spread mode
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Functionalities
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1.0
• Relative positioning
• Center positioning & bias
• Guidelines - helper objects
• Chains
• Dimension constraints: min/max, Ratio
• ConstraintSet
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Gone Behavior
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Gone Behavior
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Inadapted Margin
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Inadapted Margin
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Gone Margins
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Gone Margins
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Example
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Example
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beta 1
1.1.0
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• Barriers
beta 1
1.1.0
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• Barriers
beta 1
1.1.0
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• Barriers
beta 1
1.1.0
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Barriers
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Barriers
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Barriers
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Barriers
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Barriers
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• Barriers
• Group - apply visibility to a set of widgets
beta 1
1.1.0
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Groups
textview2
textview3
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Groups
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Groups
Invisible Gone
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• Barriers
• Group
• Placeholder
beta 1
1.1.0
?
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class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
fun select(v: View) {
TransitionManager.beginDelayedTransition(main_layout)
placeholder.setContentId(v.id)
main_title.text= v.tag as CharSequence?;"";
}
}
Placeholder
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class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
fun select(v: View) {
TransitionManager.beginDelayedTransition(main_layout)
placeholder.setContentId(v.id)
main_title.text= v.tag as CharSequence?;"";
}
}
Placeholder
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• Barriers
• Group
• Placeholder
• Percent dimensions
beta 1
1.1.0
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Dimension Constraints
• width|height set to 0dp (“match_constraint”)
• control behavior with
• app:layout_constraintWidth_default=“spread|wrap|percent”
• spread matches endpoints
• wrap behave like wrap_content, but respect constraints
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default=wrap
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default=wrap
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default=wrap
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Percent Dimension
• As a percentage of the parent container
• Not bounded by the container
• value from 0 to 1
android:layout_width="0dp"
app:layout_constraintWidth_default="percent"
app:layout_constraintWidth_percent="0.5"
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beta 1
1.1.0
maven {
url "https://maven.google.com"
}
dependencies {
...
compile 'com.android.support.constraint:constraint-layout:1.1.0-beta1'
}
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ConstraintSet
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Layout
!=
Views
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ConstraintLayout Views
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ConstraintLayout Views
ConstraintSet
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ConstraintLayout Views
ConstraintSet
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ConstraintLayout Views
ConstraintSet
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ConstraintSet
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ConstraintSet
• Separate views from how we layout them
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ConstraintSet
• Separate views from how we layout them
• Encapsulate all constraints in an object
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ConstraintSet
• Separate views from how we layout them
• Encapsulate all constraints in an object
• You can apply a ConstraintSet to an existing ConstraintLayout
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ConstraintSet
• Separate views from how we layout them
• Encapsulate all constraints in an object
• You can apply a ConstraintSet to an existing ConstraintLayout
• Switch between multiple ConstraintSet
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ConstraintSet mConstraintSet1 = new ConstraintSet();
ConstraintSet mConstraintSet2 = new ConstraintSet();
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ConstraintSet mConstraintSet1 = new ConstraintSet();
ConstraintSet mConstraintSet2 = new ConstraintSet();
// get constraints from layout
mConstraintSet2.clone(context, R.layout.state2);
setContentView(R.layout.state1);
mConstraintLayout = (ConstraintLayout)
findViewById(R.id.activity_main);
// get constraints from ConstraintSet
mConstraintSet1.clone(mConstraintLayout);
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ConstraintSet mConstraintSet1 = new ConstraintSet();
ConstraintSet mConstraintSet2 = new ConstraintSet();
// get constraints from layout
mConstraintSet2.clone(context, R.layout.state2);
setContentView(R.layout.state1);
mConstraintLayout = (ConstraintLayout)
findViewById(R.id.activity_main);
// get constraints from ConstraintSet
mConstraintSet1.clone(mConstraintLayout);
mConstraintSet1.applyTo(mConstraintLayout);
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Landscape
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Rotation
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Rotation
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Motion
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Motion
• Flat Hierarchy == No clipping issues
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Motion
• Flat Hierarchy == No clipping issues
• Scene Graph
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Motion
• Flat Hierarchy == No clipping issues
• Scene Graph
• ConstraintSet == Keyframe
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ConstraintSet mConstraintSet1 = new ConstraintSet();
ConstraintSet mConstraintSet2 = new ConstraintSet();
// get constraints from layout
mConstraintSet2.clone(context, R.layout.state2);
setContentView(R.layout.state1);
mConstraintLayout = (ConstraintLayout)
findViewById(R.id.activity_main);
// get constraints from ConstraintSet
mConstraintSet1.clone(mConstraintLayout);
mConstraintSet1.applyTo(mConstraintLayout);
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ConstraintSet mConstraintSet1 = new ConstraintSet();
ConstraintSet mConstraintSet2 = new ConstraintSet();
// get constraints from layout
mConstraintSet2.clone(context, R.layout.state2);
setContentView(R.layout.state1);
mConstraintLayout = (ConstraintLayout)
findViewById(R.id.activity_main);
// get constraints from ConstraintSet
mConstraintSet1.clone(mConstraintLayout);
mConstraintSet1.applyTo(mConstraintLayout);
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TransitionManager.beginDelayedTransition(mConstraintLayout);
ConstraintSet mConstraintSet1 = new ConstraintSet();
ConstraintSet mConstraintSet2 = new ConstraintSet();
// get constraints from layout
mConstraintSet2.clone(context, R.layout.state2);
setContentView(R.layout.state1);
mConstraintLayout = (ConstraintLayout)
findViewById(R.id.activity_main);
// get constraints from ConstraintSet
mConstraintSet1.clone(mConstraintLayout);
mConstraintSet1.applyTo(mConstraintLayout);
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ConstraintLayout : choreographer
• What you can do with widgets, you can do with components
• Everything is still the same
• Flexible
• Easy to build and test
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NavigationView
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NavigationView
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• |
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• |
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Custom Transitions
• ConstraintSet
• Custom TransitionSet
• Support library physics
TransitionManager.beginDelayedTransition(cl,
new MyCustomAnimationSet())
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Custom Transitions
• ConstraintSet
• Custom TransitionSet
• Support library physics
TransitionManager.beginDelayedTransition(cl,
new MyCustomAnimationSet())
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What’s next
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What’s next
• More performance optimizations
• experimental background resolution
• segmentation of constraints
• broadening the optimizer surface
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What’s next
• ConstraintHelper
• Chains
• Layers
• Custom
• Motion
• better motion control
• gesture support
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Documentation
• http://www.constraintlayout.com
• https://developer.android.com/reference/android/support/
constraint/package-summary.html
• https://developer.android.com/training/constraint-layout/
index.html
• https://codelabs.developers.google.com/codelabs/constraint-layout
• https://medium.com/google-developers/building-interfaces-with-
constraintlayout-3958fa38a9f7
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Documentation
• http://www.constraintlayout.com
• https://developer.android.com/reference/android/support/
constraint/package-summary.html
• https://developer.android.com/training/constraint-layout/
index.html
• https://codelabs.developers.google.com/codelabs/constraint-layout
• https://medium.com/google-developers/building-interfaces-with-
constraintlayout-3958fa38a9f7
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Thank you!
+NicolasRoard
@camaelon
http://b.android.com
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