WhileVisibleInScrollView Class

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Active while an element is positioned within the visible area of the ScrollView.

<ScrollView>
    <StackPanel>
        <Each Items="{images}">
            <DockPanel Height="100">
                <Image Url="{source}" MemoryPolicy="UnloadUnused" Dock="Left"
                    Visibility="Hidden" ux:Name="theImage"/>
                <Text Value="{description}" TextWrapping="Wrap"/>

                <WhileVisibleInScrollView>
                    <Change theImage.Visibility="Visible"/>
                </WhileVisibleInScrollView>
            </DockPanel>
        </Each>
    </StackPanel>
</ScrollView>

This example will show the images only when they are actually in the visible area. Combined with the UnloadUnused memory policy this will allow the memory to be freed when they aren't visible to the user.

If the panel has a fixed height, as in this example, you could also collapse the text to save the calculation and rendering time.

You would also use this trigger if you wish to animate something within a ScrollView. There's no point in animating something the user can't actually see; using the trigger can save resources by not animating things that aren't visible.

Note that the element itself need not necessarily be visible, but just have a layout that positions it in the visible area. Visibility="Hidden" on a Visual does not prevent the activiation of this trigger.

This trigger responds to changes in scroll position. Layout changes on the element will also update the status but layout changes further up the tree may not update the status (we do not have an efficient way to monitor for global positioning changes).

Location

Namespace: Fuse.Triggers
Package: Fuse.Controls.ScrollView 2.9.1

Show Uno properties and methods

Interface of WhileVisibleInScrollView

Distance : float ux

The maximum allowed distance away from the visible area where this trigger remains active.

Mode : WhileVisibleInScrollViewMode ux

How the bounds of an element are treated.

RelativeTo : IScrolledLength ux

The measurement used by Distance.

WhileVisibleInScrollView Constructor uno

Creates a new WhileVisibleInScrollView

Inherited from WhileTrigger

BypassSetActive(bool) uno

Call in situations where the bypassing is forced. This should be rare since during rooting the normal bypass mechanism of the trigger will apply.

Invert : bool ux

Inverts the trigger so it will be active when it would normally be inactive, and vice versa.

SetActive(bool) uno

Inherited from Trigger

Actions : IList of TriggerAction ux

A list of actions that execute with the trigger. These may react on simple direction changes, or at specific time offsets.

Activate(Action) uno

Activates the trigger (target progress of 1).

Animators : IList of Animator ux

BackwardAnimation : TriggerAnimation ux

Specifies an explicit backward animation instead of using the implied backward animation of the animators involved. Be aware that actions are not part of the animation.

Bypass : TriggerBypassMode ux

Specifies how changes in state are handled while initializing and rooting the trigger.

BypassActivate uno

BypassDeactivate uno

BypassSeek(double, AnimationVariant) uno

CrossFadeDuration : double ux

If there is a transition between forward/backward playback and two timeilnes are being used (implicit or explicit) this specifies the cross-fade time.

Deactivate uno

Deactivates the trigger (target progress of 0).

DirectActivate(Action) uno

DirectDeactivate uno

DirectSeek(double, AnimationVariant) uno

HasActions : bool uno

HasAnimators : bool uno

HasBackwardAnimation : bool uno

true if there is an explicit backward animation.

InversePulse uno

OnPlayStateChanged(TriggerPlayState) uno

OnProgressChanged uno

PlayEnd(bool, Action) uno

Play the trigger from where it currently is to the end.

PlayTo(double, AnimationVariant) uno

Plays to a specific progress with the given animation variant.

Progress : double uno

The current progress of the trigger.

Pulse uno

Plays the trigger to progress 1 then back to 0.

PulseBackward uno

Plays the trigger starting at progress=1 down to 0.

RecreateAnimationState uno

RequireLayout(Visual) uno

Indicates the trigger is bound to the layout of a visual. This will keep the trigger in Bypass mode until after the first layout of the element is obtained. This is required since layout does not happen in the same root grouping/update phase as the creation of the element, yet not having a layout should qualify as part of the rooting period.

Seek(double, AnimationVariant) uno

Seeks to a specific progress with the given animation variant.

Start uno

Stop(bool) uno

StretchDuration : double ux

Stretches the duration of the animation to fill up this period of time.

TimeMultiplier : double ux

Specifies a multiplier to the elapsed time for animation playback.

Inherited from NodeGroupBase

FindTemplate(string) : Template uno

Nodes : IList of Node ux

Nodes to add to the Parent when this trigger is any non-deactivated state (Progress > 0)

OnNodeAdded(Node) uno

OnNodeRemoved(Node) uno

Resources : IList of Resource ux

Templates : IList of Template ux

Inherited from Node

Add(Binding) uno

Bindings : IList of Binding ux

The list of bindings belonging to this node.

ContextParent : Node uno

The context parent is the semantic parent of this node. It is where non-UI structure should be resolved, like looking for the DataContext, a Navigation, or other semantic item.

FindByType<T> : T uno

FindNodeByName(Selector, Predicate<Node> (Node)) : Node uno

Finds the first node with a given name that satisfies the given acceptor. The serach algorithm works as follows: Nodes in the subtree are matched first, then it matches the nodes in the subtrees ofthe ancestor nodes by turn all the way to the root. If no matching node is found, the function returns null.

GetNearestAncestorOfType<T> : T uno

Insert(int, Binding) uno

IsRootingCompleted : bool uno

Whether rooting for this node is completed. Returns false if unrooting has started.

IsRootingStarted : bool uno

Whether rooting of this node has started. Note that even if this property returns true, rooting may not yet be completed for the node. See also IsRootingCompleted.

Name : Selector ux

Run-time name of the node. This property is automatically set using the ux:Name attribute.

NextSibling<T> : T uno

Returns the next sibling node of the given type.

OnDataChanged(string, object) uno

OnRooted uno

If you override OnRooted you must call base.OnRooted() first in your derived class. No other processing should happen first, otherwise you might end up in an undefined state.

OnUnrooted uno

Parent : Visual uno

The parent Visual of this node. Will return null if the node is not rooted.

PreviousSibling<T> : T uno