Android(安卓)Scroller类介绍
16lz
2021-12-04
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 is113 * null, the default (viscous) interpolator will be used. "Flywheel" behavior will114 * 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 is123 * null, the default (viscous) interpolator will be used. Specify whether or124 * 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 value136 * is {@link ViewConfiguration#getScrollFriction}.137 * 138 * @param friction A scalar dimension-less value representing the coefficient of139 * 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/meter148 * mPpi // pixels per inch149 * 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 be202 * 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 the247 * 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 else264 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 <= mMaxX280 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 <= mMaxY285 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 the306 * duration.307 * 308 * @param startX Starting horizontal scroll offset in pixels. Positive309 * numbers will scroll the content to the left.310 * @param startY Starting vertical scroll offset in pixels. Positive numbers311 * will scroll the content up.312 * @param dx Horizontal distance to travel. Positive numbers will scroll the313 * content to the left.314 * @param dy Vertical distance to travel. Positive numbers will scroll the315 * 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. Positive325 * numbers will scroll the content to the left.326 * @param startY Starting vertical scroll offset in pixels. Positive numbers327 * will scroll the content up.328 * @param dx Horizontal distance to travel. Positive numbers will scroll the329 * content to the left.330 * @param dy Vertical distance to travel. Positive numbers will scroll the331 * 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 will350 * 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 per355 * second.356 * @param velocityY Initial velocity of the fling (Y) measured in pixels per357 * second358 * @param minX Minimum X value. The scroller will not scroll past this359 * point.360 * @param maxX Maximum X value. The scroller will not scroll past this361 * point.362 * @param minY Minimum Y value. The scroller will not scroll past this363 * point.364 * @param maxY Maximum Y value. The scroller will not scroll past this365 * 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 progress370 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 <= mMaxX414 mFinalX = Math.min(mFinalX, mMaxX);415 mFinalX = Math.max(mFinalX, mMinX);416 417 mFinalY = startY + Math.round(totalDistance * coeffY);418 // Pin to mMinY <= mFinalY <= mMaxY419 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 y440 * position441 *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 scroll452 * 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 * @hide502 */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。
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