Appbar fitsSystemWindows - Inside a ViewPager

问题

I have an Activity that contains a ViewPager:

activity.xml:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true"/>

</FrameLayout>

The fragments this pager contains – which are all generated from the same layout – have a CoordinatorLayout and CollapsingToolbarLayout to provide a collapsing image-back titlebar:

fragment.xml:

<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/coordinator_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

    <android.support.v4.widget.NestedScrollView
        android:id="@+id/scrollview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <!-- Content here -->

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

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="256dp"
        android:elevation="8dp"
        android:fitsSystemWindows="true">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsing_toolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:expandedTitleMarginStart="72dp"
            android:fitsSystemWindows="true">

            <ImageView
                android:id="@+id/photo"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:scaleType="centerCrop"
                app:layout_collapseMode="parallax"
                android:background="@color/photo_placeholder"
                android:fitsSystemWindows="true"/>

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
                android:layout_width="match_parent"
                android:layout_height="?actionBarSize"
                app:layout_collapseMode="pin"
                android:layout_gravity="bottom">

            </android.support.v7.widget.Toolbar>

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

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

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

Without the fitsSystemWindows flags in the activity layout, the image in the fragment properly displays behind the system status bar, while the text sometimes collapses behind the status bar when scrolled up. If I add the flags in – as shown above – the text issue is resolved, but the image now cuts off at the status bar. Keeping the collapsing toolbar code in the fragment, is there a way to fit the fragment's content to the system window?

Without fitsSystemWindows in the activity (preferred behaviour):

With fitsSystemWindows in the activity:

回答1:

You haven't declared, that you want NestedScrollView also to fitSystemWindows. So, literally, you are prohibiting WindowInsets to be passed to children off NestedScrollView, thus ViewPager is not even aware about WindowInsets.

Apply android:fitSystemWindows="true" to NestedScrollView also.

来源：https://stackoverflow.com/questions/40815997/appbar-fitssystemwindows-inside-a-viewpager