F.A.B隐藏但不显示

Question

试图实现隐藏在向下滚动的Floating Action Button（F.A.B），并在向上滚动时显示。

我有ScrollAwareFABBehavior.java来管理它，它连接到XML activity_main中的F.A.B in。问题：F.A.B隐藏在向下滚动，但在向上滚动时不再显示。我记录了onNestedScroll方法，并在向下滚动时调用“调用滚动”和“调用隐藏”;但在F.A.B被隐藏之后，没有3x Log

问题：为什么在F.A.B被隐藏之后我向上滚动时没有显示F.A.B.

scroll aware FAB behavior.Java:

import android.content.Context;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;

public class ScrollAwareFABBehavior extends FloatingActionButton.Behavior {
    public ScrollAwareFABBehavior(Context context, AttributeSet attrs) {
        super();
    }

    @Override
    public boolean onStartNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child,
                                       final View directTargetChild, final View target, final int nestedScrollAxes) {
        // Ensure we react to vertical scrolling
        return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL
                || super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, nestedScrollAxes);
    }

    @Override
    public void onNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child,
                               final View target, final int dxConsumed, final int dyConsumed,
                               final int dxUnconsumed, final int dyUnconsumed) {
        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
        Log.d("test", "calling scroll");
        if (dyConsumed > 0 && child.getVisibility() == View.VISIBLE) {
            // User scrolled down and the FAB is currently visible -> hide the FAB
            Log.d("test", "calling to hide");
            child.hide();
        } else if (dyConsumed < 0 && child.getVisibility() != View.VISIBLE) {
            // User scrolled up and the FAB is currently not visible -> show the FAB
            Log.d("test", "calling to show");
            child.show();
        }
    }
}

activity_main.xml中：

<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="companyname.appname.MainActivity">


        <android.support.v7.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/rv_contactlist"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:clipToPadding="false"
            android:paddingBottom="16dp"
            android:paddingTop="16dp"
            android:scrollbars="vertical" />

        <android.support.design.widget.FloatingActionButton

            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom|end"
            android:layout_margin="16dp"
            android:src="@drawable/ic_add_circle_outline_black_24dp"
            app:layout_anchor="@id/rv_contactlist"
            app:layout_anchorGravity="bottom|right|end"
            android:layout_alignParentEnd="true"
            app:fabSize="normal"
            android:layout_alignParentBottom="true"
            android:onClick="addItem"
            app:layout_behavior="companyname.appname.ScrollAwareFABBehavior"/>

</android.support.design.widget.CoordinatorLayout>

Answer 1

您在项目中使用哪个支持库版本？

如果您使用的是最新的（我的意思是25.0.x），这是因为fab.hide（）方法将可见性设置为View.GONE。这使得嵌套滚动侦听器停止检查fab，第二次尝试滚动列表时。

更多细节可以在这里找到：https://code.google.com/p/android/issues/detail?id=230298

我搜索了一下，发现这个类似的问题已经有了一个很好的答案：Floating action button not visible on scrolling after updating Google Support & Design Library

因此，可能的解决方法是覆盖fab.hide方法，而不是将可见性设置为GONE而是将其设置为INVISIBLE。

而且我认为这可能会在以后从上游修复，所以请密切关注它。

Answer 2

因为Android更新到25.0.x +你应该设置fab按钮与监听器INVISBLE再次显示fab按钮，我的解决方案是下一个：

public class ScrollAwareFABBehavior extends FloatingActionButton.Behavior {
private static final String TAG = "ScrollAwareFABBehavior";

public ScrollAwareFABBehavior(Context context, AttributeSet attrs) {
    super();
}


@Override
public boolean onStartNestedScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull FloatingActionButton child, @NonNull View directTargetChild, @NonNull View target, int axes, int type) {
    return true;
}

@Override
public boolean layoutDependsOn(CoordinatorLayout parent, FloatingActionButton child, View dependency) {
    if(dependency instanceof RecyclerView)
        return true;

    return false;
}

@Override
public void onNestedScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull FloatingActionButton child, @NonNull View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int type) {
    super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, type);

    if (dyConsumed > 0 && child.getVisibility() == View.VISIBLE) {
        child.hide(new FloatingActionButton.OnVisibilityChangedListener() {
                       @Override
                       public void onHidden(FloatingActionButton fab) {
                           super.onHidden(fab);
                           fab.setVisibility(View.INVISIBLE);
                       }
                   }
        );
    } else if (dyConsumed < 0 && child.getVisibility() != View.VISIBLE) {
        child.show();
    }
}
}

**使用Android Oreo测试Nexus 6P。

Answer 3

使用之前建议的双重检查方法。晶圆厂可以在同一时间展示和隐藏，所以对于完美无瑕的展示工厂：

fab.show（）; fab.setVisibility（View.VISIBLE）;