CoordinatorLayout.Behavior

public Behavior()

Default constructor for instantiating Behaviors.

public Behavior(@NonNull Context context, @Nullable AttributeSet attrs)

Default constructor for inflating Behaviors from layout. The Behavior will have the opportunity to parse specially defined layout parameters. These parameters will appear on the child view tag.

public boolean blocksInteractionBelow(@NonNull CoordinatorLayout parent, @NonNull V child)

Determine whether interaction with views behind the given child in the child order should be blocked.

The default implementation returns true if getScrimOpacity would return >0.0f.

public boolean getInsetDodgeRect(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    @NonNull Rect rect
)

Called when a view is set to dodge view insets.

This method allows a behavior to update the rectangle that should be dodged. The rectangle should be in the parent's coordinate system and within the child's bounds. If not, a IllegalArgumentException is thrown.

public @ColorInt int getScrimColor(@NonNull CoordinatorLayout parent, @NonNull V child)

Supply a scrim color that will be painted behind the associated child view.

A scrim may be used to indicate that the other elements beneath it are not currently interactive or actionable, drawing user focus and attention to the views above the scrim.

The default implementation returns BLACK.

public @FloatRange(from = 0, to = 1) float getScrimOpacity(@NonNull CoordinatorLayout parent, @NonNull V child)

Determine the current opacity of the scrim behind a given child view

A scrim may be used to indicate that the other elements beneath it are not currently interactive or actionable, drawing user focus and attention to the views above the scrim.

The default implementation returns 0.0f.

public static @Nullable Object getTag(@NonNull View child)

Get the behavior-specific tag object with the given child view. This object is stored with the child view's LayoutParams.

public boolean layoutDependsOn(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    @NonNull View dependency
)

Determine whether the supplied child view has another specific sibling view as a layout dependency.

This method will be called at least once in response to a layout request. If it returns true for a given child and dependency view pair, the parent CoordinatorLayout will:

1. Always lay out this child after the dependent child is laid out, regardless of child order.
2. Call onDependentViewChanged when the dependency view's layout or position changes.

public @NonNull WindowInsetsCompat onApplyWindowInsets(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull WindowInsetsCompat insets
)

Called when the window insets have changed.

Any Behavior associated with the direct child of the CoordinatorLayout may elect to handle the window inset change on behalf of it's associated view.

public void onAttachedToLayoutParams(@NonNull CoordinatorLayout.LayoutParams params)

Called when the Behavior has been attached to a LayoutParams instance.

This will be called after the LayoutParams has been instantiated and can be modified.

public boolean onDependentViewChanged(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    @NonNull View dependency
)

Respond to a change in a child's dependent view

This method is called whenever a dependent view changes in size or position outside of the standard layout flow. A Behavior may use this method to appropriately update the child view in response.

A view's dependency is determined by layoutDependsOn or if child has set another view as it's anchor.

Note that if a Behavior changes the layout of a child via this method, it should also be able to reconstruct the correct position in onLayoutChild. onDependentViewChanged will not be called during normal layout since the layout of each child view will always happen in dependency order.

If the Behavior changes the child view's size or position, it should return true. The default implementation returns false.

public void onDependentViewRemoved(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    @NonNull View dependency
)

Respond to a child's dependent view being removed.

This method is called after a dependent view has been removed from the parent. A Behavior may use this method to appropriately update the child view in response.

A view's dependency is determined by layoutDependsOn or if child has set another view as it's anchor.

public void onDetachedFromLayoutParams()

Called when the Behavior has been detached from its holding LayoutParams instance.

This will only be called if the Behavior has been explicitly removed from the LayoutParams instance via setBehavior. It will not be called if the associated view is removed from the CoordinatorLayout or similar.

public boolean onInterceptTouchEvent(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    @NonNull MotionEvent ev
)

Respond to CoordinatorLayout touch events before they are dispatched to child views.

Behaviors can use this to monitor inbound touch events until one decides to intercept the rest of the event stream to take an action on its associated child view. This method will return false until it detects the proper intercept conditions, then return true once those conditions have occurred.

Once a Behavior intercepts touch events, the rest of the event stream will be sent to the onTouchEvent method.

This method will be called regardless of the visibility of the associated child of the behavior. If you only wish to handle touch events when the child is visible, you should add a check to isShown on the given child.

The default implementation of this method always returns false.

public boolean onLayoutChild(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    int layoutDirection
)

Called when the parent CoordinatorLayout is about the lay out the given child view.

This method can be used to perform custom or modified layout of a child view in place of the default child layout behavior. The Behavior's implementation can delegate to the standard CoordinatorLayout measurement behavior by calling parent.onLayoutChild.

If a Behavior implements onDependentViewChanged to change the position of a view in response to a dependent view changing, it should also implement onLayoutChild in such a way that respects those dependent views. onLayoutChild will always be called for a dependent view after its dependency has been laid out.

public boolean onMeasureChild(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    int parentWidthMeasureSpec,
    int widthUsed,
    int parentHeightMeasureSpec,
    int heightUsed
)

Called when the parent CoordinatorLayout is about to measure the given child view.

This method can be used to perform custom or modified measurement of a child view in place of the default child measurement behavior. The Behavior's implementation can delegate to the standard CoordinatorLayout measurement behavior by calling parent.onMeasureChild.

public boolean onNestedFling(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull View target,
    float velocityX,
    float velocityY,
    boolean consumed
)

Called when a nested scrolling child is starting a fling or an action that would be a fling.

Any Behavior associated with the direct child of the CoordinatorLayout may elect to accept the nested scroll as part of onStartNestedScroll. Each Behavior that returned true will receive subsequent nested scroll events for that nested scroll.

onNestedFling is called when the current nested scrolling child view detects the proper conditions for a fling. It reports if the child itself consumed the fling. If it did not, the child is expected to show some sort of overscroll indication. This method should return true if it consumes the fling, so that a child that did not itself take an action in response can choose not to show an overfling indication.

public boolean onNestedPreFling(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull View target,
    float velocityX,
    float velocityY
)

Called when a nested scrolling child is about to start a fling.

Any Behavior associated with the direct child of the CoordinatorLayout may elect to accept the nested scroll as part of onStartNestedScroll. Each Behavior that returned true will receive subsequent nested scroll events for that nested scroll.

onNestedPreFling is called when the current nested scrolling child view detects the proper conditions for a fling, but it has not acted on it yet. A Behavior can return true to indicate that it consumed the fling. If at least one Behavior returns true, the fling should not be acted upon by the child.

public void onNestedPreScroll(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull View target,
    int dx,
    int dy,
    @NonNull int[] consumed,
    int type
)

Called when a nested scroll in progress is about to update, before the target has consumed any of the scrolled distance.

Any Behavior associated with the direct child of the CoordinatorLayout may elect to accept the nested scroll as part of onStartNestedScroll. Each Behavior that returned true will receive subsequent nested scroll events for that nested scroll.

onNestedPreScroll is called each time the nested scroll is updated by the nested scrolling child, before the nested scrolling child has consumed the scroll distance itself. Each Behavior responding to the nested scroll will receive the same values. The CoordinatorLayout will report as consumed the maximum number of pixels in either direction that any Behavior responding to the nested scroll reported as consumed.

public void onNestedScroll(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull View target,
    int dxConsumed,
    int dyConsumed,
    int dxUnconsumed,
    int dyUnconsumed,
    int type,
    @NonNull int[] consumed
)

Called when a nested scroll in progress has updated and the target has scrolled or attempted to scroll.

Any Behavior associated with the direct child of the CoordinatorLayout may elect to accept the nested scroll as part of onStartNestedScroll. Each Behavior that returned true will receive subsequent nested scroll events for that nested scroll.

onNestedScroll is called each time the nested scroll is updated by the nested scrolling child, with both consumed and unconsumed components of the scroll supplied in pixels. Each Behavior responding to the nested scroll will receive the same values.

public void onNestedScrollAccepted(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull View directTargetChild,
    @NonNull View target,
    int axes,
    int type
)

Called when a nested scroll has been accepted by the CoordinatorLayout.

Any Behavior associated with any direct child of the CoordinatorLayout may elect to accept the nested scroll as part of onStartNestedScroll. Each Behavior that returned true will receive subsequent nested scroll events for that nested scroll.

public boolean onRequestChildRectangleOnScreen(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull Rect rectangle,
    boolean immediate
)

Called when a child of the view associated with this behavior wants a particular rectangle to be positioned onto the screen.

The contract for this method is the same as requestChildRectangleOnScreen.

public void onRestoreInstanceState(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    @NonNull Parcelable state
)

Hook allowing a behavior to re-apply a representation of its internal state that had previously been generated by onSaveInstanceState. This function will never be called with a null state.

public @Nullable Parcelable onSaveInstanceState(@NonNull CoordinatorLayout parent, @NonNull V child)

Hook allowing a behavior to generate a representation of its internal state that can later be used to create a new instance with that same state. This state should only contain information that is not persistent or can not be reconstructed later.

Behavior state is only saved when both the parent CoordinatorLayout and a view using this behavior have valid IDs set.

public boolean onStartNestedScroll(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull View directTargetChild,
    @NonNull View target,
    int axes,
    int type
)

Called when a descendant of the CoordinatorLayout attempts to initiate a nested scroll.

Any Behavior associated with any direct child of the CoordinatorLayout may respond to this event and return true to indicate that the CoordinatorLayout should act as a nested scrolling parent for this scroll. Only Behaviors that return true from this method will receive subsequent nested scroll events.

public void onStopNestedScroll(
    @NonNull CoordinatorLayout coordinatorLayout,
    @NonNull V child,
    @NonNull View target,
    int type
)

Called when a nested scroll has ended.

Any Behavior associated with any direct child of the CoordinatorLayout may elect to accept the nested scroll as part of onStartNestedScroll. Each Behavior that returned true will receive subsequent nested scroll events for that nested scroll.

onStopNestedScroll marks the end of a single nested scroll event sequence. This is a good place to clean up any state related to the nested scroll.

public boolean onTouchEvent(
    @NonNull CoordinatorLayout parent,
    @NonNull V child,
    @NonNull MotionEvent ev
)

Respond to CoordinatorLayout touch events after this Behavior has started intercepting them.

Behaviors may intercept touch events in order to help the CoordinatorLayout manipulate its child views. For example, a Behavior may allow a user to drag a UI pane open or closed. This method should perform actual mutations of view layout state.

This method will be called regardless of the visibility of the associated child of the behavior. If you only wish to handle touch events when the child is visible, you should add a check to isShown on the given child.

public static void setTag(@NonNull View child, @Nullable Object tag)

Associate a Behavior-specific tag object with the given child view. This object will be stored with the child view's LayoutParams.