public class

ScrollView

extends FrameLayout
java.lang.Object
   ↳ android.view.View
     ↳ android.view.ViewGroup
       ↳ android.widget.FrameLayout
         ↳ android.widget.ScrollView

Class Overview

Layout container for a view hierarchy that can be scrolled by the user, allowing it to be larger than the physical display. A ScrollView is a FrameLayout, meaning you should place one child in it containing the entire contents to scroll; this child may itself be a layout manager with a complex hierarchy of objects. A child that is often used is a LinearLayout in a vertical orientation, presenting a vertical array of top-level items that the user can scroll through.

The TextView class also takes care of its own scrolling, so does not require a ScrollView, but using the two together is possible to achieve the effect of a text view within a larger container.

ScrollView only supports vertical scrolling.

Summary

[Expand]
Inherited XML Attributes
From class android.widget.FrameLayout
From class android.view.ViewGroup
From class android.view.View
[Expand]
Inherited Constants
From class android.view.ViewGroup
From class android.view.View
Public Constructors
ScrollView(Context context)
ScrollView(Context context, AttributeSet attrs)
ScrollView(Context context, AttributeSet attrs, int defStyle)
Public Methods
void addView(View child, int index)
Adds a child view.
void addView(View child, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters.
void addView(View child, int index, ViewGroup.LayoutParams params)
Adds a child view with the specified layout parameters.
void addView(View child)
Adds a child view.
boolean arrowScroll(int direction)
Handle scrolling in response to an up or down arrow click.
void computeScroll()
Called by a parent to request that a child update its values for mScrollX and mScrollY if necessary.
boolean dispatchKeyEvent(KeyEvent event)
Dispatch a key event to the next view on the focus path.
boolean executeKeyEvent(KeyEvent event)
You can call this function yourself to have the scroll view perform scrolling from a key event, just as if the event had been dispatched to it by the view hierarchy.
void fling(int velocityY)
Fling the scroll view
boolean fullScroll(int direction)

Handles scrolling in response to a "home/end" shortcut press.

int getMaxScrollAmount()
boolean isFillViewport()
Indicates whether this ScrollView's content is stretched to fill the viewport.
boolean isSmoothScrollingEnabled()
boolean onInterceptTouchEvent(MotionEvent ev)
Implement this method to intercept all touch screen motion events.
boolean onTouchEvent(MotionEvent ev)
Implement this method to handle touch screen motion events.
boolean pageScroll(int direction)

Handles scrolling in response to a "page up/down" shortcut press.

void requestChildFocus(View child, View focused)
Called when a child of this parent wants focus
boolean requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate)
Called when a child of this group wants a particular rectangle to be positioned onto the screen.
void requestLayout()
Call this when something has changed which has invalidated the layout of this view.
void scrollTo(int x, int y)
Set the scrolled position of your view.

This version also clamps the scrolling to the bounds of our child.

void setFillViewport(boolean fillViewport)
Indicates this ScrollView whether it should stretch its content height to fill the viewport or not.
void setSmoothScrollingEnabled(boolean smoothScrollingEnabled)
Set whether arrow scrolling will animate its transition.
final void smoothScrollBy(int dx, int dy)
Like scrollBy(int, int), but scroll smoothly instead of immediately.
final void smoothScrollTo(int x, int y)
Like scrollTo(int, int), but scroll smoothly instead of immediately.
Protected Methods
int computeScrollDeltaToGetChildRectOnScreen(Rect rect)
Compute the amount to scroll in the Y direction in order to get a rectangle completely on the screen (or, if taller than the screen, at least the first screen size chunk of it).
int computeVerticalScrollRange()

The scroll range of a scroll view is the overall height of all of its children.

float getBottomFadingEdgeStrength()
Returns the strength, or intensity, of the bottom faded edge.
float getTopFadingEdgeStrength()
Returns the strength, or intensity, of the top faded edge.
void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding.
void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)
Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding and margins.
void onLayout(boolean changed, int l, int t, int r, int b)
Called from layout when this view should assign a size and position to each of its children.
void onMeasure(int widthMeasureSpec, int heightMeasureSpec)

Measure the view and its content to determine the measured width and the measured height.

boolean onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect)
When looking for focus in children of a scroll view, need to be a little more careful not to give focus to something that is scrolled off screen.
void onSizeChanged(int w, int h, int oldw, int oldh)
This is called during layout when the size of this view has changed.
[Expand]
Inherited Methods
From class android.widget.FrameLayout
From class android.view.ViewGroup
From class android.view.View
From class java.lang.Object
From interface android.graphics.drawable.Drawable.Callback
From interface android.view.KeyEvent.Callback
From interface android.view.ViewManager
From interface android.view.ViewParent

Public Constructors

public ScrollView (Context context)

public ScrollView (Context context, AttributeSet attrs)

public ScrollView (Context context, AttributeSet attrs, int defStyle)

Public Methods

public void addView (View child, int index)

Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.

Parameters
child the child view to add
index the position at which to add the child

public void addView (View child, ViewGroup.LayoutParams params)

Adds a child view with the specified layout parameters.

Parameters
child the child view to add
params the layout parameters to set on the child

public void addView (View child, int index, ViewGroup.LayoutParams params)

Adds a child view with the specified layout parameters.

Parameters
child the child view to add
index the position at which to add the child
params the layout parameters to set on the child

public void addView (View child)

Adds a child view. If no layout parameters are already set on the child, the default parameters for this ViewGroup are set on the child.

Parameters
child the child view to add

public boolean arrowScroll (int direction)

Handle scrolling in response to an up or down arrow click.

Parameters
direction The direction corresponding to the arrow key that was pressed
Returns
  • True if we consumed the event, false otherwise

public void computeScroll ()

Called by a parent to request that a child update its values for mScrollX and mScrollY if necessary. This will typically be done if the child is animating a scroll using a Scroller object.

public boolean dispatchKeyEvent (KeyEvent event)

Dispatch a key event to the next view on the focus path. This path runs from the top of the view tree down to the currently focused view. If this view has focus, it will dispatch to itself. Otherwise it will dispatch the next node down the focus path. This method also fires any key listeners.

Parameters
event The key event to be dispatched.
Returns
  • True if the event was handled, false otherwise.

public boolean executeKeyEvent (KeyEvent event)

You can call this function yourself to have the scroll view perform scrolling from a key event, just as if the event had been dispatched to it by the view hierarchy.

Parameters
event The key event to execute.
Returns
  • Return true if the event was handled, else false.

public void fling (int velocityY)

Fling the scroll view

Parameters
velocityY The initial velocity in the Y direction. Positive numbers mean that the finger/curor is moving down the screen, which means we want to scroll towards the top.

public boolean fullScroll (int direction)

Handles scrolling in response to a "home/end" shortcut press. This method will scroll the view to the top or bottom and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.

Parameters
direction the scroll direction: FOCUS_UP to go the top of the view or FOCUS_DOWN to go the bottom
Returns
  • true if the key event is consumed by this method, false otherwise

public int getMaxScrollAmount ()

Returns
  • The maximum amount this scroll view will scroll in response to an arrow event.

public boolean isFillViewport ()

Indicates whether this ScrollView's content is stretched to fill the viewport.

Returns
  • True if the content fills the viewport, false otherwise.

public boolean isSmoothScrollingEnabled ()

Returns
  • Whether arrow scrolling will animate its transition.

public boolean onInterceptTouchEvent (MotionEvent ev)

Implement this method to intercept all touch screen motion events. This allows you to watch events as they are dispatched to your children, and take ownership of the current gesture at any point.

Using this function takes some care, as it has a fairly complicated interaction with View.onTouchEvent(MotionEvent), and using it requires implementing that method as well as this one in the correct way. Events will be received in the following order:

  1. You will receive the down event here.
  2. The down event will be handled either by a child of this view group, or given to your own onTouchEvent() method to handle; this means you should implement onTouchEvent() to return true, so you will continue to see the rest of the gesture (instead of looking for a parent view to handle it). Also, by returning true from onTouchEvent(), you will not receive any following events in onInterceptTouchEvent() and all touch processing must happen in onTouchEvent() like normal.
  3. For as long as you return false from this function, each following event (up to and including the final up) will be delivered first here and then to the target's onTouchEvent().
  4. If you return true from here, you will not receive any following events: the target view will receive the same event but with the action ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here.

Parameters
ev The motion event being dispatched down the hierarchy.
Returns
  • Return true to steal motion events from the children and have them dispatched to this ViewGroup through onTouchEvent(). The current target will receive an ACTION_CANCEL event, and no further messages will be delivered here.

public boolean onTouchEvent (MotionEvent ev)

Implement this method to handle touch screen motion events.

Parameters
ev The motion event.
Returns
  • True if the event was handled, false otherwise.

public boolean pageScroll (int direction)

Handles scrolling in response to a "page up/down" shortcut press. This method will scroll the view by one page up or down and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.

Parameters
direction the scroll direction: FOCUS_UP to go one page up or FOCUS_DOWN to go one page down
Returns
  • true if the key event is consumed by this method, false otherwise

public void requestChildFocus (View child, View focused)

Called when a child of this parent wants focus

Parameters
child The child of this ViewParent that wants focus. This view will contain the focused view. It is not necessarily the view that actually has focus.
focused The view that is a descendant of child that actually has focus

public boolean requestChildRectangleOnScreen (View child, Rect rectangle, boolean immediate)

Called when a child of this group wants a particular rectangle to be positioned onto the screen. ViewGroups overriding this can trust that:

  • child will be a direct child of this group
  • rectangle will be in the child's coordinates

ViewGroups overriding this should uphold the contract:

  • nothing will change if the rectangle is already visible
  • the view port will be scrolled only just enough to make the rectangle visible

Parameters
child The direct child making the request.
rectangle The rectangle in the child's coordinates the child wishes to be on the screen.
immediate True to forbid animated or delayed scrolling, false otherwise
Returns
  • Whether the group scrolled to handle the operation

public void requestLayout ()

Call this when something has changed which has invalidated the layout of this view. This will schedule a layout pass of the view tree.

public void scrollTo (int x, int y)

Set the scrolled position of your view. This will cause a call to onScrollChanged(int, int, int, int) and the view will be invalidated.

This version also clamps the scrolling to the bounds of our child.

Parameters
x the x position to scroll to
y the y position to scroll to

public void setFillViewport (boolean fillViewport)

Indicates this ScrollView whether it should stretch its content height to fill the viewport or not.

Parameters
fillViewport True to stretch the content's height to the viewport's boundaries, false otherwise.

public void setSmoothScrollingEnabled (boolean smoothScrollingEnabled)

Set whether arrow scrolling will animate its transition.

Parameters
smoothScrollingEnabled whether arrow scrolling will animate its transition

public final void smoothScrollBy (int dx, int dy)

Like scrollBy(int, int), but scroll smoothly instead of immediately.

Parameters
dx the number of pixels to scroll by on the X axis
dy the number of pixels to scroll by on the Y axis

public final void smoothScrollTo (int x, int y)

Like scrollTo(int, int), but scroll smoothly instead of immediately.

Parameters
x the position where to scroll on the X axis
y the position where to scroll on the Y axis

Protected Methods

protected int computeScrollDeltaToGetChildRectOnScreen (Rect rect)

Compute the amount to scroll in the Y direction in order to get a rectangle completely on the screen (or, if taller than the screen, at least the first screen size chunk of it).

Parameters
rect The rect.
Returns
  • The scroll delta.

protected int computeVerticalScrollRange ()

The scroll range of a scroll view is the overall height of all of its children.

Returns
  • the total vertical range represented by the vertical scrollbar

    The default range is the drawing height of this view.

protected float getBottomFadingEdgeStrength ()

Returns the strength, or intensity, of the bottom faded edge. The strength is a value between 0.0 (no fade) and 1.0 (full fade). The default implementation returns 0.0 or 1.0 but no value in between. Subclasses should override this method to provide a smoother fade transition when scrolling occurs.

Returns
  • the intensity of the bottom fade as a float between 0.0f and 1.0f

protected float getTopFadingEdgeStrength ()

Returns the strength, or intensity, of the top faded edge. The strength is a value between 0.0 (no fade) and 1.0 (full fade). The default implementation returns 0.0 or 1.0 but no value in between. Subclasses should override this method to provide a smoother fade transition when scrolling occurs.

Returns
  • the intensity of the top fade as a float between 0.0f and 1.0f

protected void measureChild (View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)

Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding. The heavy lifting is done in getChildMeasureSpec.

Parameters
child The child to measure
parentWidthMeasureSpec The width requirements for this view
parentHeightMeasureSpec The height requirements for this view

protected void measureChildWithMargins (View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)

Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding and margins. The child must have MarginLayoutParams The heavy lifting is done in getChildMeasureSpec.

Parameters
child The child to measure
parentWidthMeasureSpec The width requirements for this view
widthUsed Extra space that has been used up by the parent horizontally (possibly by other children of the parent)
parentHeightMeasureSpec The height requirements for this view
heightUsed Extra space that has been used up by the parent vertically (possibly by other children of the parent)

protected void onLayout (boolean changed, int l, int t, int r, int b)

Called from layout when this view should assign a size and position to each of its children. Derived classes with children should override this method and call layout on each of their their children.

Parameters
changed This is a new size or position for this view
l Left position, relative to parent
t Top position, relative to parent
r Right position, relative to parent
b Bottom position, relative to parent

protected void onMeasure (int widthMeasureSpec, int heightMeasureSpec)

Measure the view and its content to determine the measured width and the measured height. This method is invoked by measure(int, int) and should be overriden by subclasses to provide accurate and efficient measurement of their contents.

CONTRACT: When overriding this method, you must call setMeasuredDimension(int, int) to store the measured width and height of this view. Failure to do so will trigger an IllegalStateException, thrown by measure(int, int). Calling the superclass' onMeasure(int, int) is a valid use.

The base class implementation of measure defaults to the background size, unless a larger size is allowed by the MeasureSpec. Subclasses should override onMeasure(int, int) to provide better measurements of their content.

If this method is overridden, it is the subclass's responsibility to make sure the measured height and width are at least the view's minimum height and width (getSuggestedMinimumHeight() and getSuggestedMinimumWidth()).

Parameters
widthMeasureSpec horizontal space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec.
heightMeasureSpec vertical space requirements as imposed by the parent. The requirements are encoded with View.MeasureSpec.

protected boolean onRequestFocusInDescendants (int direction, Rect previouslyFocusedRect)

When looking for focus in children of a scroll view, need to be a little more careful not to give focus to something that is scrolled off screen. This is more expensive than the default ViewGroup implementation, otherwise this behavior might have been made the default.

Parameters
direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and FOCUS_RIGHT
previouslyFocusedRect The rectangle (in this View's coordinate system) to give a finer grained hint about where focus is coming from. May be null if there is no hint.
Returns
  • Whether focus was taken.

protected void onSizeChanged (int w, int h, int oldw, int oldh)

This is called during layout when the size of this view has changed. If you were just added to the view hierarchy, you're called with the old values of 0.

Parameters
w Current width of this view.
h Current height of this view.
oldw Old width of this view.
oldh Old height of this view.