在阅读类app的文章页面中我们通常会见到这样的效果：
自从有了CoordinatorLayout之后，直接用自定义的Behavior就可以实现了。
首先自定义一个通用的VerticalScrollingBehavior来判断垂直滚动方向：
泡在网上的日子/**
* Created by Nikola on 11/22/2015.
*/
import android.content.Context;
import android.os.Parcelable;
import android.support.annotation.IntDef;
import android.support.design.widget.CoordinatorLayout;
import android.support.v4.view.WindowInsetsCompat;
import android.util.AttributeSet;
import android.view.View;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
public abstract class VerticalScrollingBehavior<V extends View> extends CoordinatorLayout.Behavior<V> {
private int mTotalDyUnconsumed = 0;
private int mTotalDy = 0;
@ScrollDirection
private int mOverScrollDirection = ScrollDirection.SCROLL_NONE;
@ScrollDirection
private int mScrollDirection = ScrollDirection.SCROLL_NONE;
public VerticalScrollingBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
public VerticalScrollingBehavior() {
super();
}
@Retention(RetentionPolicy.SOURCE)
@IntDef({ScrollDirection.SCROLL_DIRECTION_UP, ScrollDirection.SCROLL_DIRECTION_DOWN})
public @interface ScrollDirection {
int SCROLL_DIRECTION_UP = 1;
int SCROLL_DIRECTION_DOWN = -1;
int SCROLL_NONE = 0;
}
/*
@return Overscroll direction: SCROLL_DIRECTION_UP, CROLL_DIRECTION_DOWN, SCROLL_NONE
*/
@ScrollDirection
public int getOverScrollDirection() {
return mOverScrollDirection;
}
/**
* @return Scroll direction: SCROLL_DIRECTION_UP, SCROLL_DIRECTION_DOWN, SCROLL_NONE
*/
@ScrollDirection
public int getScrollDirection() {
return mScrollDirection;
}
/**
* @param coordinatorLayout
* @param child
* @param direction Direction of the overscroll: SCROLL_DIRECTION_UP, SCROLL_DIRECTION_DOWN
* @param currentOverScroll Unconsumed value, negative or positive based on the direction;
* @param totalOverScroll Cumulative value for current direction
*/
public abstract void onNestedVerticalOverScroll(CoordinatorLayout coordinatorLayout, V child, @ScrollDirection int direction, int currentOverScroll, int totalOverScroll);
/**
* @param scrollDirection Direction of the overscroll: SCROLL_DIRECTION_UP, SCROLL_DIRECTION_DOWN
*/
public abstract void onDirectionNestedPreScroll(CoordinatorLayout coordinatorLayout, V child, View target, int dx, int dy, int[] consumed, @ScrollDirection int scrollDirection);
@Override
public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, V child, View directTargetChild, View target, int nestedScrollAxes) {
return (nestedScrollAxes & View.SCROLL_AXIS_VERTICAL) != 0;
}
@Override
public void onNestedScrollAccepted(CoordinatorLayout coordinatorLayout, V child, View directTargetChild, View target, int nestedScrollAxes) {
super.onNestedScrollAccepted(coordinatorLayout, child, directTargetChild, target, nestedScrollAxes);
}
@Override
public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, V child, View target) {
super.onStopNestedScroll(coordinatorLayout, child, target);
}
@Override
public void onNestedScroll(CoordinatorLayout coordinatorLayout, V child, View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) {
super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
if (dyUnconsumed > 0 && mTotalDyUnconsumed < 0) {
mTotalDyUnconsumed = 0;
mOverScrollDirection = ScrollDirection.SCROLL_DIRECTION_UP;
} else if (dyUnconsumed < 0 && mTotalDyUnconsumed > 0) {
mTotalDyUnconsumed = 0;
mOverScrollDirection = ScrollDirection.SCROLL_DIRECTION_DOWN;
}
mTotalDyUnconsumed += dyUnconsumed;
onNestedVerticalOverScroll(coordinatorLayout, child, mOverScrollDirection, dyConsumed, mTotalDyUnconsumed);
}
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, V child, View target, int dx, int dy, int[] consumed) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
if (dy > 0 && mTotalDy < 0) {
mTotalDy = 0;
mScrollDirection = ScrollDirection.SCROLL_DIRECTION_UP;
} else if (dy < 0 && mTotalDy > 0) {
mTotalDy = 0;
mScrollDirection = ScrollDirection.SCROLL_DIRECTION_DOWN;
}
mTotalDy += dy;
onDirectionNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, mScrollDirection);
}
@Override
public boolean onNestedFling(CoordinatorLayout coordinatorLayout, V child, View target, float velocityX, float velocityY, boolean consumed) {
super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
mScrollDirection = velocityY > 0 ? ScrollDirection.SCROLL_DIRECTION_UP : ScrollDirection.SCROLL_DIRECTION_DOWN;
return onNestedDirectionFling(coordinatorLayout, child, target, velocityX, velocityY, mScrollDirection);
}
protected abstract boolean onNestedDirectionFling(CoordinatorLayout coordinatorLayout, V child, View target, float velocityX, float velocityY, @ScrollDirection int scrollDirection);
@Override
public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, V child, View target, float velocityX, float velocityY) {
return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
}
@Override
public WindowInsetsCompat onApplyWindowInsets(CoordinatorLayout coordinatorLayout, V child, WindowInsetsCompat insets) {
return super.onApplyWindowInsets(coordinatorLayout, child, insets);
}
@Override
public Parcelable onSaveInstanceState(CoordinatorLayout parent, V child) {
return super.onSaveInstanceState(parent, child);
}
}再自定义一个继承VerticalScrollingBehavior的BottomNavigationBehavior来处理底部导航的隐藏和显示动画
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.Snackbar;
import android.support.v4.view.ViewCompat;
import android.support.v4.view.ViewPropertyAnimatorCompat;
import android.support.v4.view.animation.LinearOutSlowInInterpolator;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.Interpolator;
/**
* Created by Nikola D. on 3/15/2016.
*/
public final class BottomNavigationBehavior<V extends View> extends VerticalScrollingBehavior<V> {
private static final Interpolator INTERPOLATOR = new LinearOutSlowInInterpolator();
private final BottomNavigationWithSnackbar mWithSnackBarImpl = Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP ? new LollipopBottomNavWithSnackBarImpl() : new PreLollipopBottomNavWithSnackBarImpl();
private boolean isTablet;
private boolean hidden = false;
private ViewPropertyAnimatorCompat mOffsetValueAnimator;
private int mSnackbarHeight = -1;
private boolean scrollingEnabled = true;
private boolean hideAlongSnackbar = false;
int[] attrsArray = new int[] {
android.R.attr.id };
public BottomNavigationBehavior() {
super();
}
public BottomNavigationBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
public static <V extends View> BottomNavigationBehavior<V> from(@NonNull V view) {
ViewGroup.LayoutParams params = view.getLayoutParams();
if (!(params instanceof CoordinatorLayout.LayoutParams)) {
throw new IllegalArgumentException("The view is not a child of CoordinatorLayout");
}
CoordinatorLayout.Behavior behavior = ((CoordinatorLayout.LayoutParams) params)
.getBehavior();
if (!(behavior instanceof BottomNavigationBehavior)) {
throw new IllegalArgumentException(
"The view is not associated with BottomNavigationBehavior");
}
return (BottomNavigationBehavior<V>) behavior;
}
@Override
public boolean layoutDependsOn(CoordinatorLayout parent, V child, View dependency) {
mWithSnackBarImpl.updateSnackbar(parent, dependency, child);
return dependency instanceof Snackbar.SnackbarLayout;
}
@Override
public void onDependentViewRemoved(CoordinatorLayout parent, V child, View dependency) {
updateScrollingForSnackbar(dependency, child, true);
super.onDependentViewRemoved(parent, child, dependency);
}
private void updateScrollingForSnackbar(View dependency, V child, boolean enabled) {
if (!isTablet && dependency instanceof Snackbar.SnackbarLayout) {
scrollingEnabled = enabled;
if (!hideAlongSnackbar && ViewCompat.getTranslationY(child) != 0) {
ViewCompat.setTranslationY(child, 0);
hidden = false;
hideAlongSnackbar = true;
}else if(hideAlongSnackbar){
hidden = true;
animateOffset(child, -child.getHeight());
}
}
}
@Override
public boolean onDependentViewChanged(CoordinatorLayout parent, V child, View dependency) {
updateScrollingForSnackbar(dependency, child, false);
return super.onDependentViewChanged(parent, child, dependency);
}
@Override
public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
boolean layoutChild = super.onLayoutChild(parent, child, layoutDirection);
return layoutChild;
}
@Override
public void onNestedVerticalOverScroll(CoordinatorLayout coordinatorLayout, V child, @ScrollDirection int direction, int currentOverScroll, int totalOverScroll) {
}
@Override
public void onDirectionNestedPreScroll(CoordinatorLayout coordinatorLayout, V child, View target, int dx, int dy, int[] consumed, @ScrollDirection int scrollDirection) {
handleDirection(child, scrollDirection);
}
private void handleDirection(V child, @ScrollDirection int scrollDirection) {
if (!scrollingEnabled) return;
if (scrollDirection == ScrollDirection.SCROLL_DIRECTION_DOWN && hidden) {
hidden = false;
animateOffset(child, 0);
} else if (scrollDirection == ScrollDirection.SCROLL_DIRECTION_UP && !hidden) {
hidden = true;
animateOffset(child, child.getHeight());
}
}
@Override
protected boolean onNestedDirectionFling(CoordinatorLayout coordinatorLayout, V child, View target, float velocityX, float velocityY, @ScrollDirection int scrollDirection) {
handleDirection(child, scrollDirection);
return true;
}
private void animateOffset(final V child, final int offset) {
ensureOrCancelAnimator(child);
mOffsetValueAnimator.translationY(offset).start();
}
private void ensureOrCancelAnimator(V child) {
if (mOffsetValueAnimator == null) {
mOffsetValueAnimator = ViewCompat.animate(child);
mOffsetValueAnimator.setDuration(200);
mOffsetValueAnimator.setInterpolator(INTERPOLATOR);
} else {
mOffsetValueAnimator.cancel();
}
}
public boolean isScrollingEnabled() {
return scrollingEnabled;
}
public void setScrollingEnabled(boolean scrollingEnabled) {
this.scrollingEnabled = scrollingEnabled;
}
public void setHidden(V view, boolean bottomLayoutHidden) {
if (!bottomLayoutHidden && hidden) {
animateOffset(view, 0);
} else if (bottomLayoutHidden && !hidden) {
animateOffset(view, -view.getHeight());
}
hidden = bottomLayoutHidden;
}
private interface BottomNavigationWithSnackbar {
void updateSnackbar(CoordinatorLayout parent, View dependency, View child);
}
private class PreLollipopBottomNavWithSnackBarImpl implements BottomNavigationWithSnackbar {
@Override
public void updateSnackbar(CoordinatorLayout parent, View dependency, View child) {
if (!isTablet && dependency instanceof Snackbar.SnackbarLayout) {
if (mSnackbarHeight == -1) {
mSnackbarHeight = dependency.getHeight();
}
int targetPadding = child.getMeasuredHeight();
int shadow = (int) ViewCompat.getElevation(child);
ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) dependency.getLayoutParams();
layoutParams.bottomMargin = targetPadding - shadow;
child.bringToFront();
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) {
child.getParent().requestLayout();
((View) child.getParent()).invalidate();
}
}
}
}
private class LollipopBottomNavWithSnackBarImpl implements BottomNavigationWithSnackbar {
@Override
public void updateSnackbar(CoordinatorLayout parent, View dependency, View child) {
if (!isTablet && dependency instanceof Snackbar.SnackbarLayout) {
if (mSnackbarHeight == -1) {
mSnackbarHeight = dependency.getHeight();
}
int targetPadding = (mSnackbarHeight +
child.getMeasuredHeight());
dependency.setPadding(dependency.getPaddingLeft(),
dependency.getPaddingTop(), dependency.getPaddingRight(), targetPadding
);
}
}
}
}如果绝对隐藏的速度太快，可以修改ensureOrCancelAnimator方法中的setDuration的值，这里是200。
activity_main.xml
<?xml version="1.0" encoding="utf-8"?> <android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:id="@+id/coordinatorlayout" android:layout_width="match_parent" android:layout_height="match_parent"> <android.support.v4.widget.NestedScrollView android:layout_width="match_parent" android:layout_height="match_parent"> <RelativeLayout android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:id="@+id/text_favorites" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" android:text="@string/long_text" /> <TextView android:id="@+id/text_schedules" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" android:text="@string/text_schedules" android:visibility="gone" /> <TextView android:id="@+id/text_music" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" android:text="@string/text_music" android:visibility="gone" /> </RelativeLayout> </android.support.v4.widget.NestedScrollView> <android.support.design.widget.BottomNavigationView android:id="@+id/bottom_navigation" android:layout_gravity="bottom" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true" app:itemBackground="@color/colorPrimary" app:itemIconTint="@color/white" app:itemTextColor="@color/white" app:layout_behavior=".BottomNavigationBehavior" app:menu="@menu/bottom_navigation_main" /> </android.support.design.widget.CoordinatorLayout>
其中app:layout_behavior=".BottomNavigationBehavior"为BottomNavigationBehavior类的位置，如果不在根目录还要加上包名。
类似
app:layout_behavior="com.xxx.behavior.BottomNavigationBehavior"
这里的BottomNavigationView可以是任意的view和布局，只要能保证是在页面的最底部就可以了。
在前面的动态图中，只有底部导航隐藏了，Toolbar并没有同时隐藏，其实这种需求也是很常见的，不过Toolbar的隐藏官方直接用app:layout_scrollFlags="scroll|enterAlways|snap"解决了。
<android.support.design.widget.AppBarLayout android:id="@+id/app_bar" android:layout_width="match_parent" android:layout_height="wrap_content" app:elevation="0dp" > <android.support.v7.widget.Toolbar android:id="@+id/toolbar" android:layout_width="match_parent" android:layout_height="@dimen/bar_height" android:background="@color/colorPrimary" app:contentInsetLeft="0dp" app:contentInsetStart="0dp" android:theme="@style/AppTheme.AppBarOverlay" app:layout_scrollFlags="scroll|enterAlways|snap" /> </android.support.design.widget.AppBarLayout>
本文的代码来自Bottom Navigation Behavior，对实现做了修改，删除了部分貌似无用的代码。
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