| /* |
| * Copyright 2019 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package androidx.viewpager2.widget.swipe |
| |
| import android.os.SystemClock |
| import android.view.animation.AccelerateInterpolator |
| import android.view.animation.Interpolator |
| import android.view.animation.LinearInterpolator |
| import androidx.core.view.ViewCompat |
| import androidx.viewpager2.widget.ViewPager2 |
| import androidx.viewpager2.widget.ViewPager2.ORIENTATION_HORIZONTAL |
| import kotlin.math.max |
| import kotlin.math.roundToInt |
| |
| class PageSwiperFakeDrag(private val viewPager: ViewPager2) : PageSwiper { |
| companion object { |
| // 60 fps |
| private const val FRAME_LENGTH_MS = 1000L / 60 |
| private const val FLING_DURATION_MS = 100L |
| } |
| |
| private val ViewPager2.pageSize: Int |
| get() { |
| return if (orientation == ORIENTATION_HORIZONTAL) { |
| measuredWidth - paddingLeft - paddingRight |
| } else { |
| measuredHeight - paddingTop - paddingBottom |
| } |
| } |
| |
| private val needsRtlModifier |
| get() = viewPager.orientation == ORIENTATION_HORIZONTAL && |
| ViewCompat.getLayoutDirection(viewPager) == ViewCompat.LAYOUT_DIRECTION_RTL |
| |
| override fun swipeNext() { |
| fakeDrag(.5f, interpolator = AccelerateInterpolator()) |
| } |
| |
| override fun swipePrevious() { |
| fakeDrag(-.5f, interpolator = AccelerateInterpolator()) |
| } |
| |
| fun fakeDrag( |
| relativeDragDistance: Float, |
| duration: Long = FLING_DURATION_MS, |
| interpolator: Interpolator = LinearInterpolator() |
| ) { |
| // Generate the deltas to feed to fakeDragBy() |
| val rtlModifier = if (needsRtlModifier) -1 else 1 |
| val steps = max(1, (duration / FRAME_LENGTH_MS.toFloat()).roundToInt()) |
| val distancePx = viewPager.pageSize * -relativeDragDistance * rtlModifier |
| val deltas = List(steps) { i -> |
| val currDistance = interpolator.getInterpolation((i + 1f) / steps) * distancePx |
| val prevDistance = interpolator.getInterpolation((i + 0f) / steps) * distancePx |
| currDistance - prevDistance |
| } |
| |
| // Send the fakeDrag events |
| var eventTime = SystemClock.uptimeMillis() |
| val delayMs = { eventTime - SystemClock.uptimeMillis() } |
| viewPager.post { viewPager.beginFakeDrag() } |
| for (delta in deltas) { |
| eventTime += FRAME_LENGTH_MS |
| viewPager.postDelayed({ viewPager.fakeDragBy(delta) }, delayMs()) |
| } |
| eventTime++ |
| viewPager.postDelayed({ viewPager.endFakeDrag() }, delayMs()) |
| } |
| } |
