ViewPager.java revision 388026a7c2dc75f106e60cbfbe655f5fb8b8200e
1/* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package android.support.v4.view; 18 19import android.os.Parcel; 20import android.os.Parcelable; 21 22import android.content.Context; 23import android.support.v4.os.ParcelableCompat; 24import android.support.v4.os.ParcelableCompatCreatorCallbacks; 25import android.util.AttributeSet; 26import android.util.Log; 27import android.view.MotionEvent; 28import android.view.VelocityTracker; 29import android.view.View; 30import android.view.ViewConfiguration; 31import android.view.ViewGroup; 32import android.widget.Scroller; 33 34import java.util.ArrayList; 35 36/** 37 * Layout manager that allows the user to flip left and right 38 * through pages of data. You supply an implementation of a 39 * {@link PagerAdapter} to generate the pages that the view shows. 40 * 41 * <p>Note this class is currently under early design and 42 * development. The API will likely change in later updates of 43 * the compatibility library, requiring changes to the source code 44 * of apps when they are compiled against the newer version.</p> 45 */ 46public class ViewPager extends ViewGroup { 47 private static final String TAG = "ViewPager"; 48 private static final boolean DEBUG = false; 49 50 private static final boolean USE_CACHE = false; 51 52 static class ItemInfo { 53 Object object; 54 int position; 55 boolean scrolling; 56 } 57 58 private final ArrayList<ItemInfo> mItems = new ArrayList<ItemInfo>(); 59 60 private PagerAdapter mAdapter; 61 private int mCurItem; // Index of currently displayed page. 62 private int mRestoredCurItem = -1; 63 private Parcelable mRestoredAdapterState = null; 64 private ClassLoader mRestoredClassLoader = null; 65 private Scroller mScroller; 66 private PagerAdapter.DataSetObserver mObserver; 67 68 private int mChildWidthMeasureSpec; 69 private int mChildHeightMeasureSpec; 70 private boolean mInLayout; 71 72 private boolean mScrollingCacheEnabled; 73 74 private boolean mPopulatePending; 75 private boolean mScrolling; 76 77 private boolean mIsBeingDragged; 78 private boolean mIsUnableToDrag; 79 private int mTouchSlop; 80 private float mInitialMotionX; 81 /** 82 * Position of the last motion event. 83 */ 84 private float mLastMotionX; 85 private float mLastMotionY; 86 /** 87 * ID of the active pointer. This is used to retain consistency during 88 * drags/flings if multiple pointers are used. 89 */ 90 private int mActivePointerId = INVALID_POINTER; 91 /** 92 * Sentinel value for no current active pointer. 93 * Used by {@link #mActivePointerId}. 94 */ 95 private static final int INVALID_POINTER = -1; 96 97 /** 98 * Determines speed during touch scrolling 99 */ 100 private VelocityTracker mVelocityTracker; 101 private int mMinimumVelocity; 102 private int mMaximumVelocity; 103 104 private OnPageChangeListener mOnPageChangeListener; 105 106 /** 107 * Indicates that the pager is in an idle, settled state. The current page 108 * is fully in view and no animation is in progress. 109 */ 110 public static final int SCROLL_STATE_IDLE = 0; 111 112 /** 113 * Indicates that the pager is currently being dragged by the user. 114 */ 115 public static final int SCROLL_STATE_DRAGGING = 1; 116 117 /** 118 * Indicates that the pager is in the process of settling to a final position. 119 */ 120 public static final int SCROLL_STATE_SETTLING = 2; 121 122 private int mScrollState = SCROLL_STATE_IDLE; 123 124 /** 125 * Callback interface for responding to changing state of the selected page. 126 */ 127 public interface OnPageChangeListener { 128 129 /** 130 * This method will be invoked when the current page is scrolled, either as part 131 * of a programmatically initiated smooth scroll or a user initiated touch scroll. 132 * 133 * @param position Position index of the first page currently being displayed. 134 * Page position+1 will be visible if positionOffset is nonzero. 135 * @param positionOffset Value from [0, 1) indicating the offset from the page at position. 136 * @param positionOffsetPixels Value in pixels indicating the offset from position. 137 */ 138 public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels); 139 140 /** 141 * This method will be invoked when a new page becomes selected. Animation is not 142 * necessarily complete. 143 * 144 * @param position Position index of the new selected page. 145 */ 146 public void onPageSelected(int position); 147 148 /** 149 * Called when the scroll state changes. Useful for discovering when the user 150 * begins dragging, when the pager is automatically settling to the current page, 151 * or when it is fully stopped/idle. 152 * 153 * @param state The new scroll state. 154 * @see ViewPager#SCROLL_STATE_IDLE 155 * @see ViewPager#SCROLL_STATE_DRAGGING 156 * @see ViewPager#SCROLL_STATE_SETTLING 157 */ 158 public void onPageScrollStateChanged(int state); 159 } 160 161 /** 162 * Simple implementation of the {@link OnPageChangeListener} interface with stub 163 * implementations of each method. Extend this if you do not intend to override 164 * every method of {@link OnPageChangeListener}. 165 */ 166 public static class SimpleOnPageChangeListener implements OnPageChangeListener { 167 @Override 168 public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { 169 // This space for rent 170 } 171 172 @Override 173 public void onPageSelected(int position) { 174 // This space for rent 175 } 176 177 @Override 178 public void onPageScrollStateChanged(int state) { 179 // This space for rent 180 } 181 } 182 183 public ViewPager(Context context) { 184 super(context); 185 initViewPager(); 186 } 187 188 public ViewPager(Context context, AttributeSet attrs) { 189 super(context, attrs); 190 initViewPager(); 191 } 192 193 void initViewPager() { 194 setWillNotDraw(false); 195 mScroller = new Scroller(getContext()); 196 final ViewConfiguration configuration = ViewConfiguration.get(getContext()); 197 mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration); 198 mMinimumVelocity = configuration.getScaledMinimumFlingVelocity(); 199 mMaximumVelocity = configuration.getScaledMaximumFlingVelocity(); 200 } 201 202 private void setScrollState(int newState) { 203 if (mScrollState == newState) { 204 return; 205 } 206 207 mScrollState = newState; 208 if (mOnPageChangeListener != null) { 209 mOnPageChangeListener.onPageScrollStateChanged(newState); 210 } 211 } 212 213 public void setAdapter(PagerAdapter adapter) { 214 if (mAdapter != null) { 215 mAdapter.setDataSetObserver(null); 216 } 217 218 mAdapter = adapter; 219 220 if (mAdapter != null) { 221 if (mObserver == null) { 222 mObserver = new DataSetObserver(); 223 } 224 mAdapter.setDataSetObserver(mObserver); 225 mPopulatePending = false; 226 if (mRestoredCurItem >= 0) { 227 mAdapter.restoreState(mRestoredAdapterState, mRestoredClassLoader); 228 setCurrentItemInternal(mRestoredCurItem, false, true); 229 mRestoredCurItem = -1; 230 mRestoredAdapterState = null; 231 mRestoredClassLoader = null; 232 } else { 233 populate(); 234 } 235 } 236 } 237 238 public PagerAdapter getAdapter() { 239 return mAdapter; 240 } 241 242 public void setCurrentItem(int item) { 243 mPopulatePending = false; 244 setCurrentItemInternal(item, true, false); 245 } 246 247 void setCurrentItemInternal(int item, boolean smoothScroll, boolean always) { 248 if (mAdapter == null || mAdapter.getCount() <= 0) { 249 setScrollingCacheEnabled(false); 250 return; 251 } 252 if (!always && mCurItem == item && mItems.size() != 0) { 253 setScrollingCacheEnabled(false); 254 return; 255 } 256 if (item < 0) { 257 item = 0; 258 } else if (item >= mAdapter.getCount()) { 259 item = mAdapter.getCount() - 1; 260 } 261 if (item > (mCurItem+1) || item < (mCurItem-1)) { 262 // We are doing a jump by more than one page. To avoid 263 // glitches, we want to keep all current pages in the view 264 // until the scroll ends. 265 for (int i=0; i<mItems.size(); i++) { 266 mItems.get(i).scrolling = true; 267 } 268 } 269 final boolean dispatchSelected = mCurItem != item; 270 mCurItem = item; 271 populate(); 272 if (smoothScroll) { 273 smoothScrollTo(getWidth()*item, 0); 274 if (dispatchSelected && mOnPageChangeListener != null) { 275 mOnPageChangeListener.onPageSelected(item); 276 } 277 } else { 278 if (dispatchSelected && mOnPageChangeListener != null) { 279 mOnPageChangeListener.onPageSelected(item); 280 } 281 completeScroll(); 282 scrollTo(getWidth()*item, 0); 283 } 284 } 285 286 public void setOnPageChangeListener(OnPageChangeListener listener) { 287 mOnPageChangeListener = listener; 288 } 289 290 /** 291 * Like {@link View#scrollBy}, but scroll smoothly instead of immediately. 292 * 293 * @param dx the number of pixels to scroll by on the X axis 294 * @param dy the number of pixels to scroll by on the Y axis 295 */ 296 void smoothScrollTo(int x, int y) { 297 if (getChildCount() == 0) { 298 // Nothing to do. 299 setScrollingCacheEnabled(false); 300 return; 301 } 302 int sx = getScrollX(); 303 int sy = getScrollY(); 304 int dx = x - sx; 305 int dy = y - sy; 306 if (dx == 0 && dy == 0) { 307 completeScroll(); 308 return; 309 } 310 311 setScrollingCacheEnabled(true); 312 mScrolling = true; 313 setScrollState(SCROLL_STATE_SETTLING); 314 mScroller.startScroll(sx, sy, dx, dy); 315 invalidate(); 316 } 317 318 void addNewItem(int position, int index) { 319 ItemInfo ii = new ItemInfo(); 320 ii.position = position; 321 ii.object = mAdapter.instantiateItem(this, position); 322 if (index < 0) { 323 mItems.add(ii); 324 } else { 325 mItems.add(index, ii); 326 } 327 } 328 329 void dataSetChanged() { 330 // This method only gets called if our observer is attached, so mAdapter is non-null. 331 332 boolean needPopulate = mItems.isEmpty() && mAdapter.getCount() > 0; 333 int newCurrItem = -1; 334 335 for (int i = 0; i < mItems.size(); i++) { 336 final ItemInfo ii = mItems.get(i); 337 final int newPos = mAdapter.getItemPosition(ii.object); 338 339 if (newPos == PagerAdapter.POSITION_UNCHANGED) { 340 continue; 341 } 342 343 if (newPos == PagerAdapter.POSITION_NONE) { 344 mItems.remove(i); 345 i--; 346 mAdapter.destroyItem(this, ii.position, ii.object); 347 needPopulate = true; 348 349 if (mCurItem == ii.position) { 350 // Keep the current item in the valid range 351 newCurrItem = Math.max(0, Math.min(mCurItem, mAdapter.getCount() - 1)); 352 } 353 continue; 354 } 355 356 if (ii.position != newPos) { 357 if (ii.position == mCurItem) { 358 // Our current item changed position. Follow it. 359 newCurrItem = newPos; 360 } 361 362 ii.position = newPos; 363 needPopulate = true; 364 } 365 } 366 367 if (newCurrItem >= 0) { 368 // TODO This currently causes a jump. 369 setCurrentItemInternal(newCurrItem, false, true); 370 needPopulate = true; 371 } 372 if (needPopulate) { 373 populate(); 374 requestLayout(); 375 } 376 } 377 378 void populate() { 379 if (mAdapter == null) { 380 return; 381 } 382 383 // Bail now if we are waiting to populate. This is to hold off 384 // on creating views from the time the user releases their finger to 385 // fling to a new position until we have finished the scroll to 386 // that position, avoiding glitches from happening at that point. 387 if (mPopulatePending) { 388 if (DEBUG) Log.i(TAG, "populate is pending, skipping for now..."); 389 return; 390 } 391 392 // Also, don't populate until we are attached to a window. This is to 393 // avoid trying to populate before we have restored our view hierarchy 394 // state and conflicting with what is restored. 395 if (getWindowToken() == null) { 396 return; 397 } 398 399 mAdapter.startUpdate(this); 400 401 final int startPos = mCurItem > 0 ? mCurItem - 1 : mCurItem; 402 final int N = mAdapter.getCount(); 403 final int endPos = mCurItem < (N-1) ? mCurItem+1 : N-1; 404 405 if (DEBUG) Log.v(TAG, "populating: startPos=" + startPos + " endPos=" + endPos); 406 407 // Add and remove pages in the existing list. 408 int lastPos = -1; 409 for (int i=0; i<mItems.size(); i++) { 410 ItemInfo ii = mItems.get(i); 411 if ((ii.position < startPos || ii.position > endPos) && !ii.scrolling) { 412 if (DEBUG) Log.i(TAG, "removing: " + ii.position + " @ " + i); 413 mItems.remove(i); 414 i--; 415 mAdapter.destroyItem(this, ii.position, ii.object); 416 } else if (lastPos < endPos && ii.position > startPos) { 417 // The next item is outside of our range, but we have a gap 418 // between it and the last item where we want to have a page 419 // shown. Fill in the gap. 420 lastPos++; 421 if (lastPos < startPos) { 422 lastPos = startPos; 423 } 424 while (lastPos <= endPos && lastPos < ii.position) { 425 if (DEBUG) Log.i(TAG, "inserting: " + lastPos + " @ " + i); 426 addNewItem(lastPos, i); 427 lastPos++; 428 i++; 429 } 430 } 431 lastPos = ii.position; 432 } 433 434 // Add any new pages we need at the end. 435 lastPos = mItems.size() > 0 ? mItems.get(mItems.size()-1).position : -1; 436 if (lastPos < endPos) { 437 lastPos++; 438 lastPos = lastPos > startPos ? lastPos : startPos; 439 while (lastPos <= endPos) { 440 if (DEBUG) Log.i(TAG, "appending: " + lastPos); 441 addNewItem(lastPos, -1); 442 lastPos++; 443 } 444 } 445 446 if (DEBUG) { 447 Log.i(TAG, "Current page list:"); 448 for (int i=0; i<mItems.size(); i++) { 449 Log.i(TAG, "#" + i + ": page " + mItems.get(i).position); 450 } 451 } 452 453 mAdapter.finishUpdate(this); 454 } 455 456 public static class SavedState extends BaseSavedState { 457 int position; 458 Parcelable adapterState; 459 ClassLoader loader; 460 461 public SavedState(Parcelable superState) { 462 super(superState); 463 } 464 465 @Override 466 public void writeToParcel(Parcel out, int flags) { 467 super.writeToParcel(out, flags); 468 out.writeInt(position); 469 out.writeParcelable(adapterState, flags); 470 } 471 472 @Override 473 public String toString() { 474 return "FragmentPager.SavedState{" 475 + Integer.toHexString(System.identityHashCode(this)) 476 + " position=" + position + "}"; 477 } 478 479 public static final Parcelable.Creator<SavedState> CREATOR 480 = ParcelableCompat.newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() { 481 @Override 482 public SavedState createFromParcel(Parcel in, ClassLoader loader) { 483 return new SavedState(in, loader); 484 } 485 @Override 486 public SavedState[] newArray(int size) { 487 return new SavedState[size]; 488 } 489 }); 490 491 SavedState(Parcel in, ClassLoader loader) { 492 super(in); 493 if (loader == null) { 494 loader = getClass().getClassLoader(); 495 } 496 position = in.readInt(); 497 adapterState = in.readParcelable(loader); 498 this.loader = loader; 499 } 500 } 501 502 @Override 503 public Parcelable onSaveInstanceState() { 504 Parcelable superState = super.onSaveInstanceState(); 505 SavedState ss = new SavedState(superState); 506 ss.position = mCurItem; 507 ss.adapterState = mAdapter.saveState(); 508 return ss; 509 } 510 511 @Override 512 public void onRestoreInstanceState(Parcelable state) { 513 if (!(state instanceof SavedState)) { 514 super.onRestoreInstanceState(state); 515 return; 516 } 517 518 SavedState ss = (SavedState)state; 519 super.onRestoreInstanceState(ss.getSuperState()); 520 521 if (mAdapter != null) { 522 mAdapter.restoreState(ss.adapterState, ss.loader); 523 setCurrentItemInternal(ss.position, false, true); 524 } else { 525 mRestoredCurItem = ss.position; 526 mRestoredAdapterState = ss.adapterState; 527 mRestoredClassLoader = ss.loader; 528 } 529 } 530 531 @Override 532 public void addView(View child, int index, LayoutParams params) { 533 if (mInLayout) { 534 addViewInLayout(child, index, params); 535 child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec); 536 } else { 537 super.addView(child, index, params); 538 } 539 540 if (USE_CACHE) { 541 if (child.getVisibility() != GONE) { 542 child.setDrawingCacheEnabled(mScrollingCacheEnabled); 543 } else { 544 child.setDrawingCacheEnabled(false); 545 } 546 } 547 } 548 549 ItemInfo infoForChild(View child) { 550 for (int i=0; i<mItems.size(); i++) { 551 ItemInfo ii = mItems.get(i); 552 if (mAdapter.isViewFromObject(child, ii.object)) { 553 return ii; 554 } 555 } 556 return null; 557 } 558 559 @Override 560 protected void onAttachedToWindow() { 561 super.onAttachedToWindow(); 562 if (mAdapter != null) { 563 populate(); 564 } 565 } 566 567 @Override 568 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 569 // For simple implementation, or internal size is always 0. 570 // We depend on the container to specify the layout size of 571 // our view. We can't really know what it is since we will be 572 // adding and removing different arbitrary views and do not 573 // want the layout to change as this happens. 574 setMeasuredDimension(getDefaultSize(0, widthMeasureSpec), 575 getDefaultSize(0, heightMeasureSpec)); 576 577 // Children are just made to fill our space. 578 mChildWidthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth() - 579 getPaddingLeft() - getPaddingRight(), MeasureSpec.EXACTLY); 580 mChildHeightMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight() - 581 getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY); 582 583 // Make sure we have created all fragments that we need to have shown. 584 mInLayout = true; 585 populate(); 586 mInLayout = false; 587 588 // Make sure all children have been properly measured. 589 final int size = getChildCount(); 590 for (int i = 0; i < size; ++i) { 591 final View child = getChildAt(i); 592 if (child.getVisibility() != GONE) { 593 if (DEBUG) Log.v(TAG, "Measuring #" + i + " " + child 594 + ": " + mChildWidthMeasureSpec); 595 child.measure(mChildWidthMeasureSpec, mChildHeightMeasureSpec); 596 } 597 } 598 } 599 600 @Override 601 protected void onSizeChanged(int w, int h, int oldw, int oldh) { 602 super.onSizeChanged(w, h, oldw, oldh); 603 604 // Make sure scroll position is set correctly. 605 int scrollPos = mCurItem*w; 606 if (scrollPos != getScrollX()) { 607 completeScroll(); 608 scrollTo(scrollPos, getScrollY()); 609 } 610 } 611 612 @Override 613 protected void onLayout(boolean changed, int l, int t, int r, int b) { 614 mInLayout = true; 615 populate(); 616 mInLayout = false; 617 618 final int count = getChildCount(); 619 final int width = r-l; 620 621 for (int i = 0; i < count; i++) { 622 View child = getChildAt(i); 623 ItemInfo ii; 624 if (child.getVisibility() != GONE && (ii=infoForChild(child)) != null) { 625 int loff = width*ii.position; 626 int childLeft = getPaddingLeft() + loff; 627 int childTop = getPaddingTop(); 628 if (DEBUG) Log.v(TAG, "Positioning #" + i + " " + child + " f=" + ii.object 629 + ":" + childLeft + "," + childTop + " " + child.getMeasuredWidth() 630 + "x" + child.getMeasuredHeight()); 631 child.layout(childLeft, childTop, 632 childLeft + child.getMeasuredWidth(), 633 childTop + child.getMeasuredHeight()); 634 } 635 } 636 } 637 638 @Override 639 public void computeScroll() { 640 if (DEBUG) Log.i(TAG, "computeScroll: finished=" + mScroller.isFinished()); 641 if (!mScroller.isFinished()) { 642 if (mScroller.computeScrollOffset()) { 643 if (DEBUG) Log.i(TAG, "computeScroll: still scrolling"); 644 int oldX = getScrollX(); 645 int oldY = getScrollY(); 646 int x = mScroller.getCurrX(); 647 int y = mScroller.getCurrY(); 648 649 if (oldX != x || oldY != y) { 650 scrollTo(x, y); 651 } 652 653 if (mOnPageChangeListener != null) { 654 final int width = getWidth(); 655 final int position = x / width; 656 final int offsetPixels = x % width; 657 final float offset = (float) offsetPixels / width; 658 mOnPageChangeListener.onPageScrolled(position, offset, offsetPixels); 659 } 660 661 // Keep on drawing until the animation has finished. 662 invalidate(); 663 return; 664 } 665 } 666 667 // Done with scroll, clean up state. 668 completeScroll(); 669 } 670 671 private void completeScroll() { 672 boolean needPopulate; 673 if ((needPopulate=mScrolling)) { 674 // Done with scroll, no longer want to cache view drawing. 675 setScrollingCacheEnabled(false); 676 mScroller.abortAnimation(); 677 int oldX = getScrollX(); 678 int oldY = getScrollY(); 679 int x = mScroller.getCurrX(); 680 int y = mScroller.getCurrY(); 681 if (oldX != x || oldY != y) { 682 scrollTo(x, y); 683 } 684 setScrollState(SCROLL_STATE_IDLE); 685 } 686 mPopulatePending = false; 687 mScrolling = false; 688 for (int i=0; i<mItems.size(); i++) { 689 ItemInfo ii = mItems.get(i); 690 if (ii.scrolling) { 691 needPopulate = true; 692 ii.scrolling = false; 693 } 694 } 695 if (needPopulate) { 696 populate(); 697 } 698 } 699 700 @Override 701 public boolean onInterceptTouchEvent(MotionEvent ev) { 702 /* 703 * This method JUST determines whether we want to intercept the motion. 704 * If we return true, onMotionEvent will be called and we do the actual 705 * scrolling there. 706 */ 707 708 final int action = ev.getAction() & MotionEventCompat.ACTION_MASK; 709 710 // Always take care of the touch gesture being complete. 711 if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) { 712 // Release the drag. 713 if (DEBUG) Log.v(TAG, "Intercept done!"); 714 mIsBeingDragged = false; 715 mIsUnableToDrag = false; 716 mActivePointerId = INVALID_POINTER; 717 return false; 718 } 719 720 // Nothing more to do here if we have decided whether or not we 721 // are dragging. 722 if (action != MotionEvent.ACTION_DOWN) { 723 if (mIsBeingDragged) { 724 if (DEBUG) Log.v(TAG, "Intercept returning true!"); 725 return true; 726 } 727 if (mIsUnableToDrag) { 728 if (DEBUG) Log.v(TAG, "Intercept returning false!"); 729 return false; 730 } 731 } 732 733 switch (action) { 734 case MotionEvent.ACTION_MOVE: { 735 /* 736 * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check 737 * whether the user has moved far enough from his original down touch. 738 */ 739 740 /* 741 * Locally do absolute value. mLastMotionY is set to the y value 742 * of the down event. 743 */ 744 final int activePointerId = mActivePointerId; 745 if (activePointerId == INVALID_POINTER) { 746 // If we don't have a valid id, the touch down wasn't on content. 747 break; 748 } 749 750 final int pointerIndex = MotionEventCompat.findPointerIndex(ev, activePointerId); 751 final float x = MotionEventCompat.getX(ev, pointerIndex); 752 final float dx = x - mLastMotionX; 753 final float xDiff = Math.abs(dx); 754 final float y = MotionEventCompat.getY(ev, pointerIndex); 755 final float yDiff = Math.abs(y - mLastMotionY); 756 if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff); 757 758 if (xDiff > mTouchSlop && xDiff > yDiff) { 759 if (DEBUG) Log.v(TAG, "Starting drag!"); 760 mIsBeingDragged = true; 761 setScrollState(SCROLL_STATE_DRAGGING); 762 mLastMotionX = x; 763 setScrollingCacheEnabled(true); 764 } else { 765 if (yDiff > mTouchSlop) { 766 // The finger has moved enough in the vertical 767 // direction to be counted as a drag... abort 768 // any attempt to drag horizontally, to work correctly 769 // with children that have scrolling containers. 770 if (DEBUG) Log.v(TAG, "Starting unable to drag!"); 771 mIsUnableToDrag = true; 772 } 773 } 774 break; 775 } 776 777 case MotionEvent.ACTION_DOWN: { 778 /* 779 * Remember location of down touch. 780 * ACTION_DOWN always refers to pointer index 0. 781 */ 782 mLastMotionX = mInitialMotionX = ev.getX(); 783 mLastMotionY = ev.getY(); 784 mActivePointerId = MotionEventCompat.getPointerId(ev, 0); 785 786 if (mScrollState == SCROLL_STATE_SETTLING) { 787 // Let the user 'catch' the pager as it animates. 788 mIsBeingDragged = true; 789 mIsUnableToDrag = false; 790 setScrollState(SCROLL_STATE_DRAGGING); 791 } else { 792 completeScroll(); 793 mIsBeingDragged = false; 794 mIsUnableToDrag = false; 795 } 796 797 if (DEBUG) Log.v(TAG, "Down at " + mLastMotionX + "," + mLastMotionY 798 + " mIsBeingDragged=" + mIsBeingDragged 799 + "mIsUnableToDrag=" + mIsUnableToDrag); 800 break; 801 } 802 803 case MotionEventCompat.ACTION_POINTER_UP: 804 onSecondaryPointerUp(ev); 805 break; 806 } 807 808 /* 809 * The only time we want to intercept motion events is if we are in the 810 * drag mode. 811 */ 812 return mIsBeingDragged; 813 } 814 815 @Override 816 public boolean onTouchEvent(MotionEvent ev) { 817 818 if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) { 819 // Don't handle edge touches immediately -- they may actually belong to one of our 820 // descendants. 821 return false; 822 } 823 824 if (mAdapter == null || mAdapter.getCount() == 0) { 825 // Nothing to present or scroll; nothing to touch. 826 return false; 827 } 828 829 if (mVelocityTracker == null) { 830 mVelocityTracker = VelocityTracker.obtain(); 831 } 832 mVelocityTracker.addMovement(ev); 833 834 final int action = ev.getAction(); 835 836 switch (action & MotionEventCompat.ACTION_MASK) { 837 case MotionEvent.ACTION_DOWN: { 838 /* 839 * If being flinged and user touches, stop the fling. isFinished 840 * will be false if being flinged. 841 */ 842 completeScroll(); 843 844 // Remember where the motion event started 845 mLastMotionX = mInitialMotionX = ev.getX(); 846 mActivePointerId = MotionEventCompat.getPointerId(ev, 0); 847 break; 848 } 849 case MotionEvent.ACTION_MOVE: 850 if (!mIsBeingDragged) { 851 final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId); 852 final float x = MotionEventCompat.getX(ev, pointerIndex); 853 final float xDiff = Math.abs(x - mLastMotionX); 854 final float y = MotionEventCompat.getY(ev, pointerIndex); 855 final float yDiff = Math.abs(y - mLastMotionY); 856 if (DEBUG) Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff); 857 if (xDiff > mTouchSlop && xDiff > yDiff) { 858 if (DEBUG) Log.v(TAG, "Starting drag!"); 859 mIsBeingDragged = true; 860 mLastMotionX = x; 861 setScrollState(SCROLL_STATE_DRAGGING); 862 setScrollingCacheEnabled(true); 863 } 864 } 865 if (mIsBeingDragged) { 866 // Scroll to follow the motion event 867 final int activePointerIndex = MotionEventCompat.findPointerIndex( 868 ev, mActivePointerId); 869 final float x = MotionEventCompat.getX(ev, activePointerIndex); 870 final float deltaX = mLastMotionX - x; 871 mLastMotionX = x; 872 float scrollX = getScrollX() + deltaX; 873 final int width = getWidth(); 874 875 final float leftBound = Math.max(0, (mCurItem - 1) * width); 876 final float rightBound = 877 Math.min(mCurItem + 1, mAdapter.getCount() - 1) * width; 878 if (scrollX < leftBound) { 879 scrollX = leftBound; 880 } else if (scrollX > rightBound) { 881 scrollX = rightBound; 882 } 883 // Don't lose the rounded component 884 mLastMotionX += scrollX - (int) scrollX; 885 scrollTo((int) scrollX, getScrollY()); 886 if (mOnPageChangeListener != null) { 887 final int position = (int) scrollX / width; 888 final int positionOffsetPixels = (int) scrollX % width; 889 final float positionOffset = (float) positionOffsetPixels / width; 890 mOnPageChangeListener.onPageScrolled(position, positionOffset, 891 positionOffsetPixels); 892 } 893 } 894 break; 895 case MotionEvent.ACTION_UP: 896 if (mIsBeingDragged) { 897 final VelocityTracker velocityTracker = mVelocityTracker; 898 velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity); 899 int initialVelocity = (int)VelocityTrackerCompat.getYVelocity( 900 velocityTracker, mActivePointerId); 901 mPopulatePending = true; 902 if ((Math.abs(initialVelocity) > mMinimumVelocity) 903 || Math.abs(mInitialMotionX-mLastMotionX) >= (getWidth()/3)) { 904 if (mLastMotionX > mInitialMotionX) { 905 setCurrentItemInternal(mCurItem-1, true, true); 906 } else { 907 setCurrentItemInternal(mCurItem+1, true, true); 908 } 909 } else { 910 setCurrentItemInternal(mCurItem, true, true); 911 } 912 913 mActivePointerId = INVALID_POINTER; 914 endDrag(); 915 } 916 break; 917 case MotionEvent.ACTION_CANCEL: 918 if (mIsBeingDragged) { 919 setCurrentItemInternal(mCurItem, true, true); 920 mActivePointerId = INVALID_POINTER; 921 endDrag(); 922 } 923 break; 924 case MotionEventCompat.ACTION_POINTER_DOWN: { 925 final int index = MotionEventCompat.getActionIndex(ev); 926 final float x = MotionEventCompat.getX(ev, index); 927 mLastMotionX = x; 928 mActivePointerId = MotionEventCompat.getPointerId(ev, index); 929 break; 930 } 931 case MotionEventCompat.ACTION_POINTER_UP: 932 onSecondaryPointerUp(ev); 933 mLastMotionX = MotionEventCompat.getX(ev, 934 MotionEventCompat.findPointerIndex(ev, mActivePointerId)); 935 break; 936 } 937 return true; 938 } 939 940 private void onSecondaryPointerUp(MotionEvent ev) { 941 final int pointerIndex = MotionEventCompat.getActionIndex(ev); 942 final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex); 943 if (pointerId == mActivePointerId) { 944 // This was our active pointer going up. Choose a new 945 // active pointer and adjust accordingly. 946 final int newPointerIndex = pointerIndex == 0 ? 1 : 0; 947 mLastMotionX = MotionEventCompat.getX(ev, newPointerIndex); 948 mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex); 949 if (mVelocityTracker != null) { 950 mVelocityTracker.clear(); 951 } 952 } 953 } 954 955 private void endDrag() { 956 mIsBeingDragged = false; 957 mIsUnableToDrag = false; 958 959 if (mVelocityTracker != null) { 960 mVelocityTracker.recycle(); 961 mVelocityTracker = null; 962 } 963 } 964 965 private void setScrollingCacheEnabled(boolean enabled) { 966 if (mScrollingCacheEnabled != enabled) { 967 mScrollingCacheEnabled = enabled; 968 if (USE_CACHE) { 969 final int size = getChildCount(); 970 for (int i = 0; i < size; ++i) { 971 final View child = getChildAt(i); 972 if (child.getVisibility() != GONE) { 973 child.setDrawingCacheEnabled(enabled); 974 } 975 } 976 } 977 } 978 } 979 980 private class DataSetObserver implements PagerAdapter.DataSetObserver { 981 @Override 982 public void onDataSetChanged() { 983 dataSetChanged(); 984 } 985 } 986} 987