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FadeTabIndicatorInterpolator.java
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FadeTabIndicatorInterpolator.java
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/*
* Copyright (C) 2021 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 com.google.android.material.tabs;
import static com.google.android.material.animation.AnimationUtils.lerp;
import android.graphics.RectF;
import android.graphics.drawable.Drawable;
import android.view.View;
import androidx.annotation.NonNull;
/**
* An implementation of {@link TabIndicatorInterpolator} that sequentially fades out the selected
* tab indicator from the current destination and fades it back in at its new destination.
*/
class FadeTabIndicatorInterpolator extends TabIndicatorInterpolator {
// When the indicator will disappear from the current tab and begin to reappear at the newly
// selected tab.
private static final float FADE_THRESHOLD = 0.5F;
@Override
void updateIndicatorForOffset(
TabLayout tabLayout,
View startTitle,
View endTitle,
float offset,
@NonNull Drawable indicator) {
View tab = offset < FADE_THRESHOLD ? startTitle : endTitle;
RectF bounds = calculateIndicatorWidthForTab(tabLayout, tab);
float alpha = offset < FADE_THRESHOLD
? lerp(1F, 0F, 0F, FADE_THRESHOLD, offset)
: lerp(0F, 1F, FADE_THRESHOLD, 1F, offset);
indicator.setBounds(
(int) bounds.left,
indicator.getBounds().top,
(int) bounds.right,
indicator.getBounds().bottom
);
indicator.setAlpha((int) (alpha * 255F));
}
}