package vn.evolus.droidreader.widget;
import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;
public class ScrollView extends ViewGroup {
private static final int INVALID_SCREEN = -1;
/**
* The velocity at which a fling gesture will cause us to snap to the next screen
*/
private static final int SNAP_VELOCITY = 500;
private boolean mFirstLayout = true;
private int mCurrentScreen;
private int mNextScreen = INVALID_SCREEN;
private Scroller mScroller;
private VelocityTracker mVelocityTracker;
private float mLastMotionX;
private int mScrollX;
private final static int TOUCH_STATE_REST = 0;
private final static int TOUCH_STATE_SCROLLING = 1;
private int mTouchState = TOUCH_STATE_REST;
private int mTouchSlop;
private int mMaximumVelocity;
private OnScreenSelectedListener listener;
/**
* Used to inflate the ScrollView from XML.
*
* @param context The application's context.
* @param attrs The attribtues set containing the ScrollView's customization values.
*/
public ScrollView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
/**
* Used to inflate the ScrollView from XML.
*
* @param context The application's context.
* @param attrs The attribtues set containing the ScrollView's customization values.
* @param defStyle Unused.
*/
public ScrollView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
public OnScreenSelectedListener getOnItemSelectedListener() {
return listener;
}
public void setOnItemSelectedListener(OnScreenSelectedListener listener) {
this.listener = listener;
}
View prependView = null;
public void prependView(View child) {
// we will actually add this view on measuring phase
this.prependView = child;
this.requestLayout();
}
private void prependViewInLayout() {
super.addViewInLayout(prependView, 0,
new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));
mCurrentScreen++;
mNextScreen = INVALID_SCREEN;
mScrollX = mCurrentScreen * getWidth();
scrollTo(mScrollX, 0);
prependView = null;
}
/**
* Initializes various states for this workspace.
*/
private void init() {
Context context = getContext();
mScroller = new Scroller(context);//, new BackInterpolator(Type.OUT, 2f));
mCurrentScreen = 0;
final ViewConfiguration configuration = ViewConfiguration.get(getContext());
mTouchSlop = configuration.getScaledTouchSlop() * 5;
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
mScrollX = mScroller.getCurrX();
scrollTo(mScrollX, 0);
postInvalidate();
} else if (mNextScreen != INVALID_SCREEN) {
mCurrentScreen = Math.max(0, Math.min(mNextScreen, getChildCount() - 1));
fireScreenSelectedEvent(mCurrentScreen);
mNextScreen = INVALID_SCREEN;
}
}
@Override
protected void dispatchDraw(Canvas canvas) {
// ViewGroup.dispatchDraw() supports many features we don't need:
// clip to padding, layout animation, animation listener, disappearing
// children, etc. The following implementation attempts to fast-track
// the drawing dispatch by drawing only what we know needs to be drawn.
boolean fastDraw = mTouchState != TOUCH_STATE_SCROLLING && mNextScreen == INVALID_SCREEN;
// If we are not scrolling or flinging, draw only the current screen
if (fastDraw) {
drawChild(canvas, getChildAt(mCurrentScreen), getDrawingTime());
mScrollX = mCurrentScreen * getWidth();
} else {
final long drawingTime = getDrawingTime();
// If we are flinging, draw only the current screen and the target screen
if (mNextScreen >= 0 && mNextScreen < getChildCount() &&
Math.abs(mCurrentScreen - mNextScreen) == 1) {
drawChild(canvas, getChildAt(mCurrentScreen), drawingTime);
drawChild(canvas, getChildAt(mNextScreen), drawingTime);
} else {
// If we are scrolling, draw all of our children
final int count = getChildCount();
for (int i = 0; i < count; i++) {
drawChild(canvas, getChildAt(i), drawingTime);
}
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
if (prependView != null) {
prependViewInLayout();
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int width = MeasureSpec.getSize(widthMeasureSpec);
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
if (widthMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ScrollView can only be used in EXACTLY mode.");
}
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
if (heightMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ScrollView can only be used in EXACTLY mode.");
}
// The children are given the same width and height as the workspace
final int count = getChildCount();
for (int i = 0; i < count; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
if (mFirstLayout) {
setHorizontalScrollBarEnabled(false);
scrollTo(mCurrentScreen * width, 0);
setHorizontalScrollBarEnabled(true);
mFirstLayout = false;
}
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
int childLeft = 0;
final int count = getChildCount();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
}
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
/*
* This method JUST determines whether we want to intercept the motion.
* If we return true, onTouchEvent will be called and we do the actual
* scrolling there.
*/
/*
* Shortcut the most recurring case: the user is in the dragging
* state and he is moving his finger. We want to intercept this
* motion.
*/
final int action = ev.getAction();
if ((action == MotionEvent.ACTION_MOVE) && (mTouchState != TOUCH_STATE_REST)) {
return true;
}
final float x = ev.getX();
switch (action) {
case MotionEvent.ACTION_MOVE:
/*
* mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
* whether the user has moved far enough from his original down touch.
*/
/*
* Locally do absolute value. mLastMotionX is set to the y value
* of the down event.
*/
final int xDiff = (int) Math.abs(x - mLastMotionX);
final int touchSlop = mTouchSlop;
boolean xMoved = xDiff > touchSlop;
if (xMoved) {
// Scroll if the user moved far enough along the X axis
mTouchState = TOUCH_STATE_SCROLLING;
}
break;
case MotionEvent.ACTION_DOWN:
// Remember location of down touch
mLastMotionX = x;
/*
* If being flinged and user touches the screen, initiate drag;
* otherwise don't. mScroller.isFinished should be false when
* being flinged.
*/
mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
// Release the drag
mTouchState = TOUCH_STATE_REST;
break;
}
/*
* The only time we want to intercept motion events is if we are in the
* drag mode.
*/
return mTouchState != TOUCH_STATE_REST;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
final int action = ev.getAction();
final float x = ev.getX();
switch (action) {
case MotionEvent.ACTION_DOWN:
/*
* If being flinged and user touches, stop the fling. isFinished
* will be false if being flinged.
*/
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
// Remember where the motion event started
mLastMotionX = x;
break;
case MotionEvent.ACTION_MOVE:
if (mTouchState == TOUCH_STATE_SCROLLING) {
// Scroll to follow the motion event
final int deltaX = (int) (mLastMotionX - x);
mLastMotionX = x;
if (deltaX < 0) {
if (mScrollX > 0) {
scrollBy(Math.max(-mScrollX, deltaX), 0);
mScrollX = getScrollX();
}
} else if (deltaX > 0) {
final int availableToScroll = getChildAt(getChildCount() - 1).getRight() -
mScrollX - getWidth();
if (availableToScroll > 0) {
scrollBy(Math.min(availableToScroll, deltaX), 0);
mScrollX = getScrollX();
}
}
}
break;
case MotionEvent.ACTION_UP:
if (mTouchState == TOUCH_STATE_SCROLLING) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int velocityX = (int) velocityTracker.getXVelocity();
if (velocityX > SNAP_VELOCITY && mCurrentScreen > 0) {
// Fling hard enough to move left
snapToScreen(mCurrentScreen - 1);
} else if (velocityX < -SNAP_VELOCITY && mCurrentScreen < getChildCount() - 1) {
// Fling hard enough to move right
snapToScreen(mCurrentScreen + 1);
} else {
snapToDestination();
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
mTouchState = TOUCH_STATE_REST;
break;
case MotionEvent.ACTION_CANCEL:
mTouchState = TOUCH_STATE_REST;
}
return true;
}
private void snapToDestination() {
final int screenWidth = getWidth();
final int whichScreen = (mScrollX + (screenWidth / 2)) / screenWidth;
snapToScreen(whichScreen);
}
public int getDisplayedChild() {
return mCurrentScreen;
}
public void snapToScreen(int whichScreen) {
//if (!mScroller.isFinished()) return;
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
final int screenDelta = Math.abs(whichScreen - mCurrentScreen);
mNextScreen = whichScreen;
final int newX = whichScreen * getWidth();
final int delta = newX - mScrollX;
final int duration = screenDelta * 300;
if (!mScroller.isFinished()) mScroller.abortAnimation();
mScroller.startScroll(mScrollX, 0, delta, 0, duration);
invalidate();
}
public void scrollLeft() {
if (mScroller.isFinished()) {
if (mCurrentScreen > 0) snapToScreen(mCurrentScreen - 1);
} else {
if (mNextScreen > 0) snapToScreen(mNextScreen - 1);
}
}
public void scrollRight() {
if (mScroller.isFinished()) {
if (mCurrentScreen < getChildCount() -1) snapToScreen(mCurrentScreen + 1);
} else {
if (mNextScreen < getChildCount() -1) snapToScreen(mNextScreen + 1);
}
}
private void fireScreenSelectedEvent(int selectedIndex) {
if (listener != null) {
listener.onSelected(selectedIndex);
}
}
public void showScreen(int whichScreen) {
mCurrentScreen = whichScreen;
mNextScreen = INVALID_SCREEN;
mScrollX = whichScreen * getWidth();
scrollTo(mScrollX, 0);
postInvalidate();
fireScreenSelectedEvent(whichScreen);
}
public interface OnScreenSelectedListener {
void onSelected(int selectedIndex);
}
}
|