资料：http://blog.csdn.net/gemmem/article/details/7321910
Scroller源码：
1 /*
2 * Copyright (C) 2006 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
17 package android.widget;
18
19 import android.content.Context;
20 import android.hardware.SensorManager;
21 import android.os.Build;
22 import android.util.FloatMath;
23 import android.view.ViewConfiguration;
24 import android.view.animation.AnimationUtils;
25 import android.view.animation.Interpolator;
26
27
28 /**
29 * This class encapsulates scrolling. The duration of the scroll
30 * can be passed in the constructor and specifies the maximum time that
31 * the scrolling animation should take. Past this time, the scrolling is
32 * automatically moved to its final stage and computeScrollOffset()
33 * will always return false to indicate that scrolling is over.
34 */
35 public class Scroller {
36 private int mMode;
37
38 private int mStartX;
39 private int mStartY;
40 private int mFinalX;
41 private int mFinalY;
42
43 private int mMinX;
44 private int mMaxX;
45 private int mMinY;
46 private int mMaxY;
47
48 private int mCurrX;
49 private int mCurrY;
50 private long mStartTime;
51 private int mDuration;
52 private float mDurationReciprocal;
53 private float mDeltaX;
54 private float mDeltaY;
55 private boolean mFinished;
56 private Interpolator mInterpolator;
57 private boolean mFlywheel;
58
59 private float mVelocity;
60
61 private static final int DEFAULT_DURATION = 250;
62 private static final int SCROLL_MODE = 0;
63 private static final int FLING_MODE = 1;
64
65 private static float DECELERATION_RATE = (float) (Math.log(0.75) / Math.log(0.9));
66 private static float ALPHA = 800; // pixels / seconds
67 private static float START_TENSION = 0.4f; // Tension at start: (0.4 * total T, 1.0 * Distance)
68 private static float END_TENSION = 1.0f - START_TENSION;
69 private static final int NB_SAMPLES = 100;
70 private static final float[] SPLINE = new float[NB_SAMPLES + 1];
71
72 private float mDeceleration;
73 private final float mPpi;
74
75 static {
76 float x_min = 0.0f;
77 for (int i = 0; i <= NB_SAMPLES; i++) {
78 final float t = (float) i / NB_SAMPLES;
79 float x_max = 1.0f;
80 float x, tx, coef;
81 while (true) {
82 x = x_min + (x_max - x_min) / 2.0f;
83 coef = 3.0f * x * (1.0f - x);
84 tx = coef * ((1.0f - x) * START_TENSION + x * END_TENSION) + x * x * x;
85 if (Math.abs(tx - t) < 1E-5) break;
86 if (tx > t) x_max = x;
87 else x_min = x;
88 }
89 final float d = coef + x * x * x;
90 SPLINE[i] = d;
91 }
92 SPLINE[NB_SAMPLES] = 1.0f;
93
94 // This controls the viscous fluid effect (how much of it)
95 sViscousFluidScale = 8.0f;
96 // must be set to 1.0 (used in viscousFluid())
97 sViscousFluidNormalize = 1.0f;
98 sViscousFluidNormalize = 1.0f / viscousFluid(1.0f);
99 }
100
101 private static float sViscousFluidScale;
102 private static float sViscousFluidNormalize;
103
104 /**
105 * Create a Scroller with the default duration and interpolator.
106 */
107 public Scroller(Context context) {
108 this(context, null);
109 }
110
111 /**
112 * Create a Scroller with the specified interpolator. If the interpolator is
113 * null, the default (viscous) interpolator will be used. "Flywheel" behavior will
114 * be in effect for apps targeting Honeycomb or newer.
115 */
116 public Scroller(Context context, Interpolator interpolator) {
117 this(context, interpolator,
118 context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.HONEYCOMB);
119 }
120
121 /**
122 * Create a Scroller with the specified interpolator. If the interpolator is
123 * null, the default (viscous) interpolator will be used. Specify whether or
124 * not to support progressive "flywheel" behavior in flinging.
125 */
126 public Scroller(Context context, Interpolator interpolator, boolean flywheel) {
127 mFinished = true;
128 mInterpolator = interpolator;
129 mPpi = context.getResources().getDisplayMetrics().density * 160.0f;
130 mDeceleration = computeDeceleration(ViewConfiguration.getScrollFriction());
131 mFlywheel = flywheel;
132 }
133
134 /**
135 * The amount of friction applied to flings. The default value
136 * is {@link ViewConfiguration#getScrollFriction}.
137 *
138 * @param friction A scalar dimension-less value representing the coefficient of
139 * friction.
140 */
141 public final void setFriction(float friction) {
142 mDeceleration = computeDeceleration(friction);
143 }
144
145 private float computeDeceleration(float friction) {
146 return SensorManager.GRAVITY_EARTH // g (m/s^2)
147 * 39.37f // inch/meter
148 * mPpi // pixels per inch
149 * friction;
150 }
151
152 /**
153 *
154 * Returns whether the scroller has finished scrolling.
155 *
156 * @return True if the scroller has finished scrolling, false otherwise.
157 */
158 public final boolean isFinished() {
159 return mFinished;
160 }
161
162 /**
163 * Force the finished field to a particular value.
164 *
165 * @param finished The new finished value.
166 */
167 public final void forceFinished(boolean finished) {
168 mFinished = finished;
169 }
170
171 /**
172 * Returns how long the scroll event will take, in milliseconds.
173 *
174 * @return The duration of the scroll in milliseconds.
175 */
176 public final int getDuration() {
177 return mDuration;
178 }
179
180 /**
181 * Returns the current X offset in the scroll.
182 *
183 * @return The new X offset as an absolute distance from the origin.
184 */
185 public final int getCurrX() {
186 return mCurrX;
187 }
188
189 /**
190 * Returns the current Y offset in the scroll.
191 *
192 * @return The new Y offset as an absolute distance from the origin.
193 */
194 public final int getCurrY() {
195 return mCurrY;
196 }
197
198 /**
199 * Returns the current velocity.
200 *
201 * @return The original velocity less the deceleration. Result may be
202 * negative.
203 */
204 public float getCurrVelocity() {
205 return mVelocity - mDeceleration * timePassed() / 2000.0f;
206 }
207
208 /**
209 * Returns the start X offset in the scroll.
210 *
211 * @return The start X offset as an absolute distance from the origin.
212 */
213 public final int getStartX() {
214 return mStartX;
215 }
216
217 /**
218 * Returns the start Y offset in the scroll.
219 *
220 * @return The start Y offset as an absolute distance from the origin.
221 */
222 public final int getStartY() {
223 return mStartY;
224 }
225
226 /**
227 * Returns where the scroll will end. Valid only for "fling" scrolls.
228 *
229 * @return The final X offset as an absolute distance from the origin.
230 */
231 public final int getFinalX() {
232 return mFinalX;
233 }
234
235 /**
236 * Returns where the scroll will end. Valid only for "fling" scrolls.
237 *
238 * @return The final Y offset as an absolute distance from the origin.
239 */
240 public final int getFinalY() {
241 return mFinalY;
242 }
243
244 /**
245 * Call this when you want to know the new location. If it returns true,
246 * the animation is not yet finished. loc will be altered to provide the
247 * new location.
248 */
249 public boolean computeScrollOffset() {
250 if (mFinished) {
251 return false;
252 }
253
254 int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);
255
256 if (timePassed < mDuration) {
257 switch (mMode) {
258 case SCROLL_MODE:
259 float x = timePassed * mDurationReciprocal;
260
261 if (mInterpolator == null)
262 x = viscousFluid(x);
263 else
264 x = mInterpolator.getInterpolation(x);
265
266 mCurrX = mStartX + Math.round(x * mDeltaX);
267 mCurrY = mStartY + Math.round(x * mDeltaY);
268 break;
269 case FLING_MODE:
270 final float t = (float) timePassed / mDuration;
271 final int index = (int) (NB_SAMPLES * t);
272 final float t_inf = (float) index / NB_SAMPLES;
273 final float t_sup = (float) (index + 1) / NB_SAMPLES;
274 final float d_inf = SPLINE[index];
275 final float d_sup = SPLINE[index + 1];
276 final float distanceCoef = d_inf + (t - t_inf) / (t_sup - t_inf) * (d_sup - d_inf);
277
278 mCurrX = mStartX + Math.round(distanceCoef * (mFinalX - mStartX));
279 // Pin to mMinX <= mCurrX <= mMaxX
280 mCurrX = Math.min(mCurrX, mMaxX);
281 mCurrX = Math.max(mCurrX, mMinX);
282
283 mCurrY = mStartY + Math.round(distanceCoef * (mFinalY - mStartY));
284 // Pin to mMinY <= mCurrY <= mMaxY
285 mCurrY = Math.min(mCurrY, mMaxY);
286 mCurrY = Math.max(mCurrY, mMinY);
287
288 if (mCurrX == mFinalX && mCurrY == mFinalY) {
289 mFinished = true;
290 }
291
292 break;
293 }
294 }
295 else {
296 mCurrX = mFinalX;
297 mCurrY = mFinalY;
298 mFinished = true;
299 }
300 return true;
301 }
302
303 /**
304 * Start scrolling by providing a starting point and the distance to travel.
305 * The scroll will use the default value of 250 milliseconds for the
306 * duration.
307 *
308 * @param startX Starting horizontal scroll offset in pixels. Positive
309 * numbers will scroll the content to the left.
310 * @param startY Starting vertical scroll offset in pixels. Positive numbers
311 * will scroll the content up.
312 * @param dx Horizontal distance to travel. Positive numbers will scroll the
313 * content to the left.
314 * @param dy Vertical distance to travel. Positive numbers will scroll the
315 * content up.
316 */
317 public void startScroll(int startX, int startY, int dx, int dy) {
318 startScroll(startX, startY, dx, dy, DEFAULT_DURATION);
319 }
320
321 /**
322 * Start scrolling by providing a starting point and the distance to travel.
323 *
324 * @param startX Starting horizontal scroll offset in pixels. Positive
325 * numbers will scroll the content to the left.
326 * @param startY Starting vertical scroll offset in pixels. Positive numbers
327 * will scroll the content up.
328 * @param dx Horizontal distance to travel. Positive numbers will scroll the
329 * content to the left.
330 * @param dy Vertical distance to travel. Positive numbers will scroll the
331 * content up.
332 * @param duration Duration of the scroll in milliseconds.
333 */
334 public void startScroll(int startX, int startY, int dx, int dy, int duration) {
335 mMode = SCROLL_MODE;
336 mFinished = false;
337 mDuration = duration;
338 mStartTime = AnimationUtils.currentAnimationTimeMillis();
339 mStartX = startX;
340 mStartY = startY;
341 mFinalX = startX + dx;
342 mFinalY = startY + dy;
343 mDeltaX = dx;
344 mDeltaY = dy;
345 mDurationReciprocal = 1.0f / (float) mDuration;
346 }
347
348 /**
349 * Start scrolling based on a fling gesture. The distance travelled will
350 * depend on the initial velocity of the fling.
351 *
352 * @param startX Starting point of the scroll (X)
353 * @param startY Starting point of the scroll (Y)
354 * @param velocityX Initial velocity of the fling (X) measured in pixels per
355 * second.
356 * @param velocityY Initial velocity of the fling (Y) measured in pixels per
357 * second
358 * @param minX Minimum X value. The scroller will not scroll past this
359 * point.
360 * @param maxX Maximum X value. The scroller will not scroll past this
361 * point.
362 * @param minY Minimum Y value. The scroller will not scroll past this
363 * point.
364 * @param maxY Maximum Y value. The scroller will not scroll past this
365 * point.
366 */
367 public void fling(int startX, int startY, int velocityX, int velocityY,
368 int minX, int maxX, int minY, int maxY) {
369 // Continue a scroll or fling in progress
370 if (mFlywheel && !mFinished) {
371 float oldVel = getCurrVelocity();
372
373 float dx = (float) (mFinalX - mStartX);
374 float dy = (float) (mFinalY - mStartY);
375 float hyp = FloatMath.sqrt(dx * dx + dy * dy);
376
377 float ndx = dx / hyp;
378 float ndy = dy / hyp;
379
380 float oldVelocityX = ndx * oldVel;
381 float oldVelocityY = ndy * oldVel;
382 if (Math.signum(velocityX) == Math.signum(oldVelocityX) &&
383 Math.signum(velocityY) == Math.signum(oldVelocityY)) {
384 velocityX += oldVelocityX;
385 velocityY += oldVelocityY;
386 }
387 }
388
389 mMode = FLING_MODE;
390 mFinished = false;
391
392 float velocity = FloatMath.sqrt(velocityX * velocityX + velocityY * velocityY);
393
394 mVelocity = velocity;
395 final double l = Math.log(START_TENSION * velocity / ALPHA);
396 mDuration = (int) (1000.0 * Math.exp(l / (DECELERATION_RATE - 1.0)));
397 mStartTime = AnimationUtils.currentAnimationTimeMillis();
398 mStartX = startX;
399 mStartY = startY;
400
401 float coeffX = velocity == 0 ? 1.0f : velocityX / velocity;
402 float coeffY = velocity == 0 ? 1.0f : velocityY / velocity;
403
404 int totalDistance =
405 (int) (ALPHA * Math.exp(DECELERATION_RATE / (DECELERATION_RATE - 1.0) * l));
406
407 mMinX = minX;
408 mMaxX = maxX;
409 mMinY = minY;
410 mMaxY = maxY;
411
412 mFinalX = startX + Math.round(totalDistance * coeffX);
413 // Pin to mMinX <= mFinalX <= mMaxX
414 mFinalX = Math.min(mFinalX, mMaxX);
415 mFinalX = Math.max(mFinalX, mMinX);
416
417 mFinalY = startY + Math.round(totalDistance * coeffY);
418 // Pin to mMinY <= mFinalY <= mMaxY
419 mFinalY = Math.min(mFinalY, mMaxY);
420 mFinalY = Math.max(mFinalY, mMinY);
421 }
422
423 static float viscousFluid(float x)
424 {
425 x *= sViscousFluidScale;
426 if (x < 1.0f) {
427 x -= (1.0f - (float)Math.exp(-x));
428 } else {
429 float start = 0.36787944117f; // 1/e == exp(-1)
430 x = 1.0f - (float)Math.exp(1.0f - x);
431 x = start + x * (1.0f - start);
432 }
433 x *= sViscousFluidNormalize;
434 return x;
435 }
436
437 /**
438 * Stops the animation. Contrary to {@link #forceFinished(boolean)},
439 * aborting the animating cause the scroller to move to the final x and y
440 * position
441 *
442 * @see #forceFinished(boolean)
443 */
444 public void abortAnimation() {
445 mCurrX = mFinalX;
446 mCurrY = mFinalY;
447 mFinished = true;
448 }
449
450 /**
451 * Extend the scroll animation. This allows a running animation to scroll
452 * further and longer, when used with {@link #setFinalX(int)} or {@link #setFinalY(int)}.
453 *
454 * @param extend Additional time to scroll in milliseconds.
455 * @see #setFinalX(int)
456 * @see #setFinalY(int)
457 */
458 public void extendDuration(int extend) {
459 int passed = timePassed();
460 mDuration = passed + extend;
461 mDurationReciprocal = 1.0f / mDuration;
462 mFinished = false;
463 }
464
465 /**
466 * Returns the time elapsed since the beginning of the scrolling.
467 *
468 * @return The elapsed time in milliseconds.
469 */
470 public int timePassed() {
471 return (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);
472 }
473
474 /**
475 * Sets the final position (X) for this scroller.
476 *
477 * @param newX The new X offset as an absolute distance from the origin.
478 * @see #extendDuration(int)
479 * @see #setFinalY(int)
480 */
481 public void setFinalX(int newX) {
482 mFinalX = newX;
483 mDeltaX = mFinalX - mStartX;
484 mFinished = false;
485 }
486
487 /**
488 * Sets the final position (Y) for this scroller.
489 *
490 * @param newY The new Y offset as an absolute distance from the origin.
491 * @see #extendDuration(int)
492 * @see #setFinalX(int)
493 */
494 public void setFinalY(int newY) {
495 mFinalY = newY;
496 mDeltaY = mFinalY - mStartY;
497 mFinished = false;
498 }
499
500 /**
501 * @hide
502 */
503 public boolean isScrollingInDirection(float xvel, float yvel) {
504 return !mFinished && Math.signum(xvel) == Math.signum(mFinalX - mStartX) &&
505 Math.signum(yvel) == Math.signum(mFinalY - mStartY);
506 }
507 }
Scroller源码只有507行，结合链接中资料发现，Scroller只是一个计算滚动位置的帮助类，用来计算出当前应该滚动到的位置，而且每次获取位置必须调用computeScrollOffset方法才能刷新，Scroller还是很好用的，按照这个思路，以后如果滑动需要特殊计算可以按照Scroller自定义一个计算类。
时间： 2024-11-23 18:41:05