虽然RecyclerView没有足够的内容可以滚动,但AppBarLayout中的工具栏是可滚动的

Question

AppBarLayout中的工具栏是否真的可以滚动,尽管带有"appbar_scrolling_view_behavior"的主容器没有足够的内容来真正滚动？

到目前为止我测试的内容:
当我使用NestedScrollView(带有"wrap_content"属性)作为主容器而TextView作为子容器时,AppBarLayout正常工作并且不滚动.

但是,当我使用仅包含少量条目的RecyclerView和"wrap_content"属性(因此无需滚动)时,即使RecyclerView从未收到滚动事件(使用OnScrollChangeListener测试),AppBarLayout中的工具栏也是可滚动的).

这是我的布局代码:

<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.design.widget.AppBarLayout
        android:id="@+id/appBarLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways"
            app:theme="@style/ToolbarStyle" />
    </android.support.design.widget.AppBarLayout>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</android.support.design.widget.CoordinatorLayout>

具有以下效果,工具栏可滚动,虽然没有必要:

我还通过检查所有RecyclerView项目是否可见并使用RecyclerView的setNestedScrollingEnabled()方法找到了解决此问题的方法.
尽管如此,它似乎更像是我想要的错误.任何意见？:d

编辑#1:

对于可能对我当前的解决方案感兴趣的人,我不得不将setNestedScrollingEnabled()逻辑放在Handler的postDelayed()方法中,延迟时间为5毫秒,因为LayoutManager在调用方法时总是返回-1第一个和最后一个项目是否可见.
我在onStart()方法中使用此代码(在我的RecyclerView初始化之后)以及每次发生RecyclerView内容更改后.

final LinearLayoutManager layoutManager = (LinearLayoutManager) mRecyclerView.getLayoutManager();
new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        //no items in the RecyclerView
        if (mRecyclerView.getAdapter().getItemCount() == 0)
            mRecyclerView.setNestedScrollingEnabled(false);
        //if the first and the last item is visible
        else if (layoutManager.findFirstCompletelyVisibleItemPosition() == 0
                && layoutManager.findLastCompletelyVisibleItemPosition() == mRecyclerView.getAdapter().getItemCount() - 1)
            mRecyclerView.setNestedScrollingEnabled(false);
        else
            mRecyclerView.setNestedScrollingEnabled(true);
    }
}, 5);

编辑#2:

我只是玩了一个新的应用程序,似乎这个(非预期的)行为已经在支持库版本23.3.0(甚至更早)中得到修复.因此,不再需要解决方法!

Answer 1

编辑2:

当RecyclerView不可滚动时,确保工具栏不可滚动的唯一方法是以编程方式设置setScrollFlags,这需要检查RecyclerView是否可滚动.每次修改适配器时都必须进行此检查.

与Activity通信的接口:

public interface LayoutController {
    void enableScroll();
    void disableScroll();
}

主要活动:

public class MainActivity extends AppCompatActivity implements 
    LayoutController {

    private CollapsingToolbarLayout collapsingToolbarLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        collapsingToolbarLayout = 
              (CollapsingToolbarLayout) findViewById(R.id.collapsing_toolbar);

        final FragmentManager manager = getSupportFragmentManager();
        final Fragment fragment = new CheeseListFragment();
        manager.beginTransaction()
                .replace(R.id.root_content, fragment)
                .commit();
    }

    @Override
    public void enableScroll() {
        final AppBarLayout.LayoutParams params = (AppBarLayout.LayoutParams)
                                  collapsingToolbarLayout.getLayoutParams();
        params.setScrollFlags(
                AppBarLayout.LayoutParams.SCROLL_FLAG_SCROLL 
                | AppBarLayout.LayoutParams.SCROLL_FLAG_ENTER_ALWAYS
        );
        collapsingToolbarLayout.setLayoutParams(params);
    }

    @Override
    public void disableScroll() {
        final AppBarLayout.LayoutParams params = (AppBarLayout.LayoutParams)
                                  collapsingToolbarLayout.getLayoutParams();
        params.setScrollFlags(0);
        collapsingToolbarLayout.setLayoutParams(params);
    }
}

activity_main.xml中:

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/drawer_layout"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:fitsSystemWindows="true">

    <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/main_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.AppBarLayout
            android:id="@+id/appbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

            <android.support.design.widget.CollapsingToolbarLayout
                android:id="@+id/collapsing_toolbar"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:fitsSystemWindows="true"
                app:contentScrim="?attr/colorPrimary">

                <android.support.v7.widget.Toolbar
                    android:id="@+id/toolbar"
                    android:layout_width="match_parent"
                    android:layout_height="?attr/actionBarSize"
                    android:background="?attr/colorPrimary"
                    app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

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

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

        <FrameLayout
            android:id="@+id/root_content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="fill_vertical"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"/>

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

</android.support.v4.widget.DrawerLayout>

测试片段:

public class CheeseListFragment extends Fragment {

    private static final int DOWN = 1;
    private static final int UP = 0;

    private LayoutController controller;
    private RecyclerView rv;

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);

        try {
            controller = (MainActivity) getActivity();
        } catch (ClassCastException e) {
            throw new RuntimeException(getActivity().getLocalClassName()
                    + "must implement controller.", e);
        }
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        rv = (RecyclerView) inflater.inflate(
                R.layout.fragment_cheese_list, container, false);
        setupRecyclerView(rv);

        // Find out if RecyclerView are scrollable, delay required
        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                if (rv.canScrollVertically(DOWN) || rv.canScrollVertically(UP)) {
                    controller.enableScroll();
                } else {
                    controller.disableScroll();
                }
            }
        }, 100);

        return rv;
    }

    private void setupRecyclerView(RecyclerView recyclerView) {
        final LinearLayoutManager layoutManager = new LinearLayoutManager(recyclerView.getContext());

        recyclerView.setLayoutManager(layoutManager);

        final SimpleStringRecyclerViewAdapter adapter =
                new SimpleStringRecyclerViewAdapter(
                        getActivity(),
                        // Test ToolBar scroll
                        getRandomList(/* with enough items to scroll */)
                        // Test ToolBar pin
                        getRandomList(/* with only 3 items*/)
                );

        recyclerView.setAdapter(adapter);
    }
}

资料来源:

• 以编程方式更改滚动标记
• Chris Banes的原始代码
• 需要postDelayed以确保RecyclerView子项已准备好进行计算

编辑:

您应该使用CollapsingToolbarLayout来控制行为.

直接将工具栏添加到AppBarLayout可以访问enterAlwaysCollapsed和exitUntilCollapsed滚动标记,但不能详细控制不同元素对折叠的反应.[...]安装程序使用CollapsingToolbarLayout的应用程序:layout_collapseMode ="pin"以确保在视图折叠时工具栏本身仍然固定在屏幕顶部.http://android-developers.blogspot.com.tr/2015/05/android-design-support-library.html

<android.support.design.widget.CollapsingToolbarLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_scrollFlags="scroll|exitUntilCollapsed">

    <android.support.v7.widget.Toolbar
        android:id="@+id/drawer_toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        app:layout_collapseMode="pin"/>

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

加

app:layout_collapseMode="pin"

到xml中的工具栏.

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:layout_scrollFlags="scroll|enterAlways"
        app:layout_collapseMode="pin"
        app:theme="@style/ToolbarStyle" />

Answer 2

所以,适当的信用,这个答案几乎解决了它为我/sf/answers/2304625851/.但是,当你实际上有一个可滚动的recyclerview并且它的最后一个项目可见时它没有显示工具栏(它不会在第一个向上滚动时显示工具栏),我决定修改它并调整它以便更容易实现和动态适配器.

首先,您必须为appbar创建自定义布局行为:

public class ToolbarBehavior extends AppBarLayout.Behavior{

private boolean scrollableRecyclerView = false;
private int count;

public ToolbarBehavior() {
}

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

@Override
public boolean onInterceptTouchEvent(CoordinatorLayout parent, AppBarLayout child, MotionEvent ev) {
    return scrollableRecyclerView && super.onInterceptTouchEvent(parent, child, ev);
}

@Override
public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child, View directTargetChild, View target, int nestedScrollAxes, int type) {
    updatedScrollable(directTargetChild);
    return scrollableRecyclerView && super.onStartNestedScroll(parent, child, directTargetChild, target, nestedScrollAxes, type);
}

@Override
public boolean onNestedFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY, boolean consumed) {
    return scrollableRecyclerView && super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
}

private void updatedScrollable(View directTargetChild) {
    if (directTargetChild instanceof RecyclerView) {
        RecyclerView recyclerView = (RecyclerView) directTargetChild;
        RecyclerView.Adapter adapter = recyclerView.getAdapter();
        if (adapter != null) {
            if (adapter.getItemCount()!= count) {
                scrollableRecyclerView = false;
                count = adapter.getItemCount();
                RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
                if (layoutManager != null) {
                    int lastVisibleItem = 0;
                    if (layoutManager instanceof LinearLayoutManager) {
                        LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
                        lastVisibleItem = Math.abs(linearLayoutManager.findLastCompletelyVisibleItemPosition());
                    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
                        StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) layoutManager;
                        int[] lastItems = staggeredGridLayoutManager.findLastCompletelyVisibleItemPositions(new int[staggeredGridLayoutManager.getSpanCount()]);
                        lastVisibleItem = Math.abs(lastItems[lastItems.length - 1]);
                    }
                    scrollableRecyclerView = lastVisibleItem < count - 1;
                }
            }
        }
    } else scrollableRecyclerView = true;
  }
}

然后,您只需要在布局文件中为appbar定义此行为:

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:fitsSystemWindows="true"
    app:layout_behavior="com.yourappname.whateverdir.ToolbarBehavior"
    >

我没有测试它的屏幕旋转,所以让我知道它是否像这样工作.我想它应该可以工作,因为我不认为在旋转发生时会保存计数变量,但如果没有,请告诉我.

这对我来说是最简单,最干净的实现,享受它.

Answer 3

在你Toolbar删除scroll标志时，只留下enterAlways标志，你应该得到你想要的效果。为了完整起见，您的布局应如下所示：

<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.design.widget.AppBarLayout
        android:id="@+id/appBarLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="enterAlways"
            app:theme="@style/ToolbarStyle" />
    </android.support.design.widget.AppBarLayout>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</android.support.design.widget.CoordinatorLayout>