Develop Reference

How do I get a floating button like uber

I want to create a floating button like Uber. Uber shows a floating button when online and hides it when offline. Also "DU recorder" app has the floating button.
I want the floating button remain on top of all apps and be movable on any place on screen.
I have Samsung Galaxy S7 Edge with Android 8 (Oreo)

use this code
import android.content.Context;
import android.support.design.widget.FloatingActionButton;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
public class MovableFloatingActionButton extends FloatingActionButton implements View.OnTouchListener {
private final static float CLICK_DRAG_TOLERANCE = 10; // Often, there will be a slight, unintentional, drag when the user taps the FAB, so we need to account for this.
private float downRawX, downRawY;
private float dX, dY;
public MovableFloatingActionButton(Context context) {
super(context);
init();
}
public MovableFloatingActionButton(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public MovableFloatingActionButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
setOnTouchListener(this);
}
#Override
public boolean onTouch(View view, MotionEvent motionEvent){
int action = motionEvent.getAction();
if (action == MotionEvent.ACTION_DOWN) {
downRawX = motionEvent.getRawX();
downRawY = motionEvent.getRawY();
dX = view.getX() - downRawX;
dY = view.getY() - downRawY;
return true; // Consumed
}
else if (action == MotionEvent.ACTION_MOVE) {
int viewWidth = view.getWidth();
int viewHeight = view.getHeight();
View viewParent = (View)view.getParent();
int parentWidth = viewParent.getWidth();
int parentHeight = viewParent.getHeight();
float newX = motionEvent.getRawX() + dX;
newX = Math.max(0, newX); // Don't allow the FAB past the left hand side of the parent
newX = Math.min(parentWidth - viewWidth, newX); // Don't allow the FAB past the right hand side of the parent
float newY = motionEvent.getRawY() + dY;
newY = Math.max(0, newY); // Don't allow the FAB past the top of the parent
newY = Math.min(parentHeight - viewHeight, newY); // Don't allow the FAB past the bottom of the parent
view.animate()
.x(newX)
.y(newY)
.setDuration(0)
.start();
return true; // Consumed
}
else if (action == MotionEvent.ACTION_UP) {
float upRawX = motionEvent.getRawX();
float upRawY = motionEvent.getRawY();
float upDX = upRawX - downRawX;
float upDY = upRawY - downRawY;
if (Math.abs(upDX) < CLICK_DRAG_TOLERANCE && Math.abs(upDY) < CLICK_DRAG_TOLERANCE) { // A click
return performClick();
}
else { // A drag
return true; // Consumed
}
}
else {
return super.onTouchEvent(motionEvent);
}
}
}
//-------------------this code inside the xml file -----------
<com.example.MovableFloatingActionButton
android:id="#+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="#dimen/fab_margin"
android:src="#drawable/ic_navigate_next_white_24dp"/>

Your question contains multiple questions so let us break it down and take it to step by step.
For Creating Floating Button:
I would say use #Vishal Sharma answer about this question in this page
And about showing and hiding it when the user is online or offline:
public class NetworkStateReceiver extends BroadcastReceiver {
protected Set<NetworkStateReceiverListener> listeners;
protected Boolean connected;
public NetworkStateReceiver() {
listeners = new HashSet<NetworkStateReceiverListener>();
connected = null;
}
public void onReceive(Context context, Intent intent) {
if(intent == null || intent.getExtras() == null)
return;
ConnectivityManager manager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo ni = manager.getActiveNetworkInfo();
if(ni != null && ni.getState() == NetworkInfo.State.CONNECTED) {
connected = true;
} else if(intent.getBooleanExtra(ConnectivityManager.EXTRA_NO_CONNECTIVITY,Boolean.FALSE)) {
connected = false;
}
notifyStateToAll();
}
private void notifyStateToAll() {
for(NetworkStateReceiverListener listener : listeners)
notifyState(listener);
}
private void notifyState(NetworkStateReceiverListener listener) {
if(connected == null || listener == null)
return;
if(connected == true)
listener.networkAvailable();
else
listener.networkUnavailable();
}
public void addListener(NetworkStateReceiverListener l) {
listeners.add(l);
notifyState(l);
}
public void removeListener(NetworkStateReceiverListener l) {
listeners.remove(l);
}
public interface NetworkStateReceiverListener {
public void networkAvailable();
public void networkUnavailable();
}
}
YOUR ACTIVITY:
public class MyActivity implements NetworkStateReceiverListener {
private NetworkStateReceiver networkStateReceiver;
}
IN YOUR ACTIVITY: INSTANTIATE THE RECEIVER
public void onCreate(Bundle savedInstanceState) {
networkStateReceiver = new NetworkStateReceiver();
networkStateReceiver.addListener(this);
this.registerReceiver(networkStateReceiver, new IntentFilter(android.net.ConnectivityManager.CONNECTIVITY_ACTION));
}
public void onDestroy() {
super.onDestroy();
networkStateReceiver.removeListener(this);
this.unregisterReceiver(networkStateReceiver);
}
IN YOUR ACTIVITY: IMPLEMENTS THE REQUIRED METHODS
#Override
public void networkAvailable() {
/* TODO: show your button here */
}
#Override
public void networkUnavailable() {
/* TODO: hide your button here */
}

Android transfer touch event between views

Here is my issue.
I have about 7 buttons inside a linear layout and i am trying to "slide" between them highlighting each one as the finger passes over.
So far i have seen that the view that receives the action down event is locked in and receives every following motion event untill action up.
here is what i was trying:
public class LinearRoot extends LinearLayout {
#SuppressWarnings("unused")
private static final String TAG = LinearRoot.class.getSimpleName();
public LinearRoot(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
private LinearRoot(Context context) {
super(context);
init();
}
private void init() {
getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
for (int i = 0; i < getChildCount(); i++) {
Rect r = new Rect();
getChildAt(i).getHitRect(r);
Log.e(TAG, r.flattenToString());
map.put(r, getChildAt(i));
}
LinearRoot.this.getViewTreeObserver().removeGlobalOnLayoutListener(this);
}
});
}
/* (non-Javadoc)
* #see android.view.ViewGroup#onInterceptTouchEvent(android.view.MotionEvent)
*/
View lastView;
private final HashMap<Rect, View> map = new HashMap<Rect, View>();
#Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
return false;
}
Rect rect = new Rect();
if (lastView != null) {
lastView.getGlobalVisibleRect(rect);
if (dispatchTouchToSpecificView(rect, ev)) {
lastView.dispatchTouchEvent(ev);
return false;
} else {
ev.setAction(MotionEvent.ACTION_CANCEL);
lastView.dispatchTouchEvent(ev);
}
}
Iterator<Rect> iterator = map.keySet().iterator();
while (iterator.hasNext()) {
rect = iterator.next();
if (dispatchTouchToSpecificView(rect, ev)) {
lastView = map.get(rect);
map.get(rect).dispatchTouchEvent(ev);
return false;
}
}
return false;
}
private boolean dispatchTouchToSpecificView(Rect r, MotionEvent ev) {
Log.e(TAG, "X: " + (int) ev.getX() + " Y" + (int) ev.getY());
Log.e(TAG, r.flattenToString());
return r.contains((int) ev.getRawX(), (int) ev.getRawY());
}
}
This is the root layout for all the buttons, which delegates the touch events to the appropriate button by getting its global hit rectangle and seeing if the touch event is inside.
Right now this works only partially, and i am not satisfied with the solution, please provide some comments or possibilities to try.
What i am trying to achieve is a layout that has a large number of buttons which are pretty small and i want to highlight the touched ones before the release so the user can adjust his click.

Make a scrollView autoscroll with drag and drop in Android

I searched all over, but could not find a solution.
I have a view (lets call it myView) inside a scrollview. myView is bigger than the screen. Since I'm able to get the relative x,y position of my finger inside myView, I would like to make the scrollView autoscroll to the top/bottom when my finger enters a certain top/bottom threshold.
I have some ideas, namely translating the drag location to the screen position but this did not solve this problem.
thanks in advance
cheers

All right I figured it out by myself.
First I had to extend the ScrollView class and added an interface OnScrollViewListener.
public class MyScrollView extends ScrollView {
private OnScrollViewListener mListener;
public MyScrollView(Context c, AttributeSet attrs) {
super(c, attrs);
}
#Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
super.onScrollChanged(l, t, oldl, oldt);
if (mListener != null) {
mListener.onScrollChanged((OnScrollViewListener) this);
}
}
public void setOnScrollViewListener(OnScrollViewListener listener) {
mListener = listener;
}
public static interface OnScrollViewListener {
public void onScrollChanged(OnScrollViewListener listener);
}
}
Next in my Activity I inserted a member mScrollDistance that indicates the amount of
pixels the user scrolls.
public class ScrollActivity extends Activity {
private int mScrollDistance;
#Override
protected void OnCreate(...) {
...
final MyScrollView myScrollView = (MyScrollView) findViewById(R.id.scroll_view);
myScrollView.setOnScrollViewListener(new MyScrollView.OnScrollViewListener() {
public void onScrollChanged(OnScrollViewListener listener) {
mScrollDistance = listener.getScrollY();
}
}
// making an drag and drop in an view that is inside the MyScrollView
final LinearLayout myLayout = (LinearLayout)findViewById(R.id.linear_layout);
myLayout.setOnDragListener(new View.OnDragListener() {
public boolean onDrag (View v, DragEvent event) {
int action = event.getAction();
switch(action) {
case DragEvent.ACTION_DRAG_STARTED: {
}
case DragEvent.ACTION_DRAG_LOCATION: {
int y = Math.round(event.getY());
int translatedY = y - mScrollDistance;
int threshold = 50;
// make a scrolling up due the y has passed the threshold
if (translatedY < threshold) {
// make a scroll up by 30 px
myScrollView.scrollBy(0, -30);
}
// make a autoscrolling down due y has passed the 500 px border
if (translatedY + threshold > 500) {
// make a scroll down by 30 px
myScrollView.scrollBy(0, 30);
}
// listen for more actions here
// ...
}
}
}
}
Now, mScrollDistance gets always a new value and the drag location will be translated to the view location.
I tested this and it works on layouts/views that are bigger than the screen size.
Hope that helps.

I came up with a different solution and I am happy with it.
I want to be able to drag and drop views inside a ScrollView. The ScrollView then needs to scroll up and down automatically when the shadow reaches the edges of the scroll view.
I ended up with a solution that detects wether the drop zone is completely visible inside the scrollview (with a 100px margin) and adjust the scroll view otherwise.
#Override
public boolean onDrag(View view, DragEvent event) {
MainWidget dropZoneView = (MainWidget) view;
int action = event.getAction();
switch (action) {
case DragEvent.ACTION_DRAG_STARTED:
//(... other stuff happens here)
case DragEvent.ACTION_DRAG_LOCATION:
ScrollView mainScrollView = (ScrollView) findViewById(R.id.main_scroll);
int topOfDropZone = dropZoneView.getTop();
int bottomOfDropZone = dropZoneView.getBottom();
int scrollY = mainScrollView.getScrollY();
int scrollViewHeight = mainScrollView.getMeasuredHeight();
Log.d(LOG_TAG,"location: Scroll Y: "+ scrollY + " Scroll Y+Height: "+(scrollY + scrollViewHeight));
Log.d(LOG_TAG," top: "+ topOfDropZone +" bottom: "+bottomOfDropZone);
if (bottomOfDropZone > (scrollY + scrollViewHeight - 100))
mainScrollView.smoothScrollBy(0, 30);
if (topOfDropZone < (scrollY + 100))
mainScrollView.smoothScrollBy(0, -30);
break;
default:
break;
}
return true;
}
Hope this helps!

I used a timer in In C#
ScrollCalendar ScrollCalendar = new ScrollCalendar (yourScrollView);
Inside the drag event
public bool OnDrag (View v, DragEvent e)
{
var dragshadow = new EventDateDragShadow (v);
switch (e.Action) {
case DragAction.Started:
return true;
case DragAction.Entered:
break;
case Android.Views.DragAction.Location:
if (e.GetY () < 90) {
ScrollCalendar.StartScroll (-15);
} else if (e.GetY () > yourScrollView.Height - 90) {
ScrollCalendar.StartScroll (15);
} else
ScrollCalendar.StopScroll ();
return (true);
case DragAction.Exited:
return true;
case DragAction.Drop:
return true;
case DragAction.Ended:
ScrollCalendar.StopScroll ();
v.SetOnDragListener (null);
return true;
}
return true;
}
The ScrollCalendar class
public class ScrollCalendar
{
private ScrollView Calendar;
private System.Timers.Timer Timer;
private int ScrollDistance;
public ScrollCalendar(ScrollView calendar)
{
Calendar = calendar;
Timer = new System.Timers.Timer();
Timer.Elapsed+=new ElapsedEventHandler(Scroll);
Timer.Interval = 50;
}
public void StartScroll(int scrollDistance)
{
if (Timer.Enabled) {
return;
}
ScrollDistance = scrollDistance;
Timer.Enabled = true;
}
public void StopScroll()
{
Timer.Enabled = false;
}
private void Scroll(object source, ElapsedEventArgs e)
{
Calendar.SmoothScrollBy (0, ScrollDistance);
}
}
Change the StartScroll value and the Timer.Interval to adjust the speed of the scroll.

I have modified answer of Tiago A.
I faced the same problem and the solution from Tiago A was small and easy but have some limitation so if others require this may help.
Thanks to Tiago A.
case DragEvent.ACTION_DRAG_LOCATION:
ScrollView myScrollView =findViewById(R.id.myScrollView);
int topOfDropZone = myScrollView.getChildAt(0).getTop();
int bottomOfDropZone = myScrollView.getChildAt(0).getBottom();
int scrollY = myScrollView.getScrollY();
int scrollViewHeight = myScrollView.getMeasuredHeight();
if (Math.round(event.getY()) > scrollViewHeight - (scrollViewHeight / 45))
if (bottomOfDropZone > (scrollY + scrollViewHeight - 100))
myScrollView.smoothScrollBy(0, 30);
if (Math.round(event.getY()) < (scrollViewHeight / 45))
if (topOfDropZone < (scrollY + 100))
myScrollView.smoothScrollBy(0, -30);
return true;

Making a relative layout's content larger than the screen

I am making a grid-based game that will be much larger than the screen, and the user would scroll around in it. I basically put a bunch on ImageViews inside of a custom class that extends a relative layout. The problem is that even though RelativeLayout.LayoutParams is set to the correct size I want (1280*1280). The images are crammed against the sides of the screen and don't extend past it. I have got the scrolling logic working, and when I scroll, I can see it is a rectangle of images the size of one screen. How can I make it so the images extend past the screen?
The class that extends a relative layout:
public class GameGrid extends RelativeLayout {
ImageView[][] subViews;
int rows=0, cols=0, cellsize=0;
int width, height;
//Dragging variables
float startX;
float startY;
float lastX;
float lastY;
boolean touching;
boolean dragging;
int clickedChild;
public GameGrid(Context context) {
super(context);
init();
}
public GameGrid(Context context, int rws, int cls, int clsze) {
super(context);
rows=rws;
cols=cls;
cellsize=clsze;
init();
}
public GameGrid(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public GameGrid(Context context, AttributeSet attrs, int defaultStyles) {
super(context, attrs, defaultStyles);
init();
}
public void init() {
rows=10;
cols=10;
cellsize=128;
startX = 0;
startY = 0;
lastX=0;
lastY=0;
touching = false;
dragging = false;
clickedChild = -1;
subViews = new ImageView[cols][rows];
setLayoutParams(new RelativeLayout.LayoutParams(cellsize*cols,cellsize*rows));
width=this.getLayoutParams().width;
height=this.getLayoutParams().height;
this.setMinimumWidth(width);
this.setMinimumHeight(height);
Log.i("info","****************");
Log.i("info","GameGrid Made.");
Log.i("info","width: "+width+"\nheight: "+height);
Log.i("info","****************");
makeGrid();
// this.setOnTouchListener()
}
public boolean getDragging(){
return dragging;
}
public void makeGrid() {
for(int y=0;y<rows;y++){
for(int x=0;x<cols;x++){
ImageView temp = new ImageView(getContext());
temp.setImageResource(R.drawable.water1);
temp.setScaleType(ImageView.ScaleType.FIT_XY);
RelativeLayout.LayoutParams temp2 = new RelativeLayout.LayoutParams(width/cols,height/rows);
if (x == 0 && y == 0){ //If this is the first view being made, set it relative to the parent.
temp2.addRule(RelativeLayout.ALIGN_PARENT_TOP);
temp2.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
}
else if (x == 0){ //If this is in the first column, set it below the one above.
temp2.addRule(RelativeLayout.ALIGN_LEFT,subViews[0][y-1].getId());
temp2.addRule(RelativeLayout.BELOW,subViews[0][y-1].getId());
}
else { //Align the bottom with first one of that row.
temp2.addRule(RelativeLayout.RIGHT_OF,subViews[x-1][y].getId());
temp2.addRule(RelativeLayout.ALIGN_BOTTOM,subViews[0][y].getId());
}
temp.setLayoutParams(temp2);
subViews[x][y]=temp;
subViews[x][y].setId(x+y*cols+1);
// Toast.makeText(getContext(), "" + v.getId(), Toast.LENGTH_SHORT).show();
subViews[x][y].setOnTouchListener(new OnTouchListener() {
public boolean onTouch(View v,MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN)
clickedChild = v.getId();
return false;
}
});
addView(temp);
}
}
}
#Override
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN)
{ // when the user touches the screen
startX = event.getX();
startY = event.getY();
lastX = event.getX();
lastY = event.getY();
touching = true;
dragging = false;
return true;
}
else if (event.getAction() == MotionEvent.ACTION_MOVE)
{ // when the user moves the touch
if (!dragging)
dragging = true;
int distX = (int)(event.getX()-lastX);
int distY = (int)(event.getY()-lastY);
this.scrollBy(-distX, -distY);
lastX = event.getX();
lastY = event.getY();
return true;
}
else if (event.getAction() == MotionEvent.ACTION_UP)
{ // when the user lifts the touch
if (!dragging){
if (clickedChild>0){
Toast.makeText(getContext(), "getHeight()= " + getHeight(), Toast.LENGTH_SHORT).show();
clickedChild = -1;
}
}
touching = false;
dragging = false;
return true;
}
else if (event.getAction() == MotionEvent.ACTION_CANCEL)
{ // if something gets lost in translation
startX = 0;
startY = 0;
lastX=0;
lastY=0;
touching = false;
dragging = false;
return true;
}
return false;
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec){
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int parentWidth = MeasureSpec.getSize(widthMeasureSpec);
int parentHeight = MeasureSpec.getSize(heightMeasureSpec);
this.setMeasuredDimension(parentWidth, parentHeight);
}
The Activity:
public class Attacktics2 extends Activity {
/** Called when the activity is first created. */
GameGrid grid;
int rows, cols, cellsize;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
}
public void start(View view) {
view.setVisibility(View.GONE);
grid = new GameGrid(this,10,10,128);
setContentView(grid);
}
}

Since you're already doing the heavy lifting of managing all the scrolling, I'd suggest that you implement your entire layout logic yourself and not rely on RelativeLayout. Except for ScrollView and HorizontalScrollView, the stock layout classes are going to restrict their children to be within the parent bounds. Those, in turn, will be restricted to the screen dimensions. If you handle the layout logic yourself, you can position child views so that they extend off screen. It then forms a viewport into a larger grid and can just render those children that are visible within the viewport.

Android: Scroller Animation?

I'm a newbie in Android development, and I would just like to know a little bit about the Scroller widget (android.widget.Scroller). How does it animate the view? Can the Animation object, if it exists, be accessed? If so, how? I've read the source code, but could find no clues, or maybe I'm too new?
I just wanted to do some operations after a Scroller finishes scrolling, something like
m_scroller.getAnimation().setAnimationListener(...);

The Scroller widget doesn't actually do much of the work at all for you. It doesn't fire any callbacks, it doesn't animate anything, it just responds to various method calls.
So what good is it? Well, it does all of the calculation for e.g. a fling for you, which is handy. So what you'd generally do is create a Runnable that repeatedly asks the Scroller, "What should my scroll position be now? Are we done flinging yet?" Then you repost that runnable on a Handler (usually on the View) until the fling is done.
Here's an example from a Fragment I'm working on right now:
private class Flinger implements Runnable {
private final Scroller scroller;
private int lastX = 0;
Flinger() {
scroller = new Scroller(getActivity());
}
void start(int initialVelocity) {
int initialX = scrollingView.getScrollX();
int maxX = Integer.MAX_VALUE; // or some appropriate max value in your code
scroller.fling(initialX, 0, initialVelocity, 0, 0, maxX, 0, 10);
Log.i(TAG, "starting fling at " + initialX + ", velocity is " + initialVelocity + "");
lastX = initialX;
getView().post(this);
}
public void run() {
if (scroller.isFinished()) {
Log.i(TAG, "scroller is finished, done with fling");
return;
}
boolean more = scroller.computeScrollOffset();
int x = scroller.getCurrX();
int diff = lastX - x;
if (diff != 0) {
scrollingView.scrollBy(diff, 0);
lastX = x;
}
if (more) {
getView().post(this);
}
}
boolean isFlinging() {
return !scroller.isFinished();
}
void forceFinished() {
if (!scroller.isFinished()) {
scroller.forceFinished(true);
}
}
}
The details of using Scroller.startScroll should be similar.

like Bill Phillips said, Scroller is just an Android SDK class helping with calculating scrolling positions. I have a full working example here:
public class SimpleScrollableView extends TextView {
private Scroller mScrollEventChecker;
private int mLastFlingY;
private float mLastY;
private float mDeltaY;
public SimpleScrollableView(Context context) {
this(context, null, 0);
}
public SimpleScrollableView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public SimpleScrollableView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
#Override
public boolean onTouchEvent(MotionEvent event) {
if (mScrollEventChecker != null && !mScrollEventChecker.isFinished()) {
return super.onTouchEvent(event);
}
final int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
mLastY = event.getY();
return true;
case MotionEvent.ACTION_MOVE:
int movingDelta = (int) (event.getY() - mLastY);
mDeltaY += movingDelta;
offsetTopAndBottom(movingDelta);
invalidate();
return true;
case MotionEvent.ACTION_UP:
mScrollEventChecker = new Scroller(getContext());
mScrollEventChecker.startScroll(0, 0, 0, (int) -mDeltaY, 1000);
post(new Runnable() {
#Override
public void run() {
if (mScrollEventChecker.computeScrollOffset()) {
int curY = mScrollEventChecker.getCurrY();
int delta = curY - mLastFlingY;
offsetTopAndBottom(delta); // this is the method make this view move
invalidate();
mLastFlingY = curY;
post(this);
} else {
mLastFlingY = 0;
mDeltaY = 0;
}
}
});
return super.onTouchEvent(event);
}
return super.onTouchEvent(event);
}
}
The demo custom view above will scroll back to original position after the user release the view. When user release the view, then startScroll() method is invoked and we can know what the distance value should be for every single message post.
Full working example: Github repository

Great answer above. Scroller#startScroll(...) indeed works the same way.
For example, the source for a custom scrolling TextView at:
http://bear-polka.blogspot.com/2009/01/scrolltextview-scrolling-textview-for.html
Sets a Scroller on a TextView using TextView#setScroller(Scroller).
The source for the SDK's TextView at:
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/2.2_r1.1/android/widget/TextView.java#TextView.0mScroller
Shows that TextView#setScroller(Scroller) sets a class field which is used in situations like bringPointIntoView(int) where Scroller#scrollTo(int, int, int, int) is called.
bringPointIntoView() adjusts mScrollX and mScrollY (with some SDK fragmentation code), then calls invalidate(). The point of all this is that mScrollX and mScrollY are used in methods like onPreDraw(...) to affect the position of the drawn contents of the view.

We can extend the Scroller class then intercept corresponding animation start methods to mark that was started, after computeScrollOffset() return false which means animation finished's value, we inform by a Listener to caller :
public class ScrollerImpl extends Scroller {
...Constructor...
private boolean mIsStarted;
private OnFinishListener mOnFinishListener;
#Override
public boolean computeScrollOffset() {
boolean result = super.computeScrollOffset();
if (!result && mIsStarted) {
try { // Don't let any exception impact the scroll animation.
mOnFinishListener.onFinish();
} catch (Exception e) {}
mIsStarted = false;
}
return result;
}
#Override
public void startScroll(int startX, int startY, int dx, int dy) {
super.startScroll(startX, startY, dx, dy);
mIsStarted = true;
}
#Override
public void startScroll(int startX, int startY, int dx, int dy, int duration) {
super.startScroll(startX, startY, dx, dy, duration);
mIsStarted = true;
}
#Override
public void fling(int startX, int startY, int velocityX, int velocityY, int minX, int maxX, int minY, int maxY) {
super.fling(startX, startY, velocityX, velocityY, minX, maxX, minY, maxY);
mIsStarted = true;
}
public void setOnFinishListener(OnFinishListener onFinishListener) {
mOnFinishListener = onFinishListener;
}
public static interface OnFinishListener {
void onFinish();
}
}