fitsSystemWindows effect gone for fragments added

问题:

I have an Activity with navigation drawer and full-bleed Fragment (with image in the top that must appear behind translucent system bar on Lollipop). While I had an interim solution where the Fragment was inflated by simply having <fragment> tag in Activity's XML, it looked fine.

Then I had to replace <fragment> with <FrameLayout> and perform fragment transactions, and now the fragment does not appear behind the system bar anymore, despite fitsSystemWindows is set to true across all required hierarchy.

I believe there might be some difference between how <fragment> gets inflated within Activity's layout vs on its own. I googled and found some solutions for KitKat, but neither of those worked for me (Lollipop).

activity.xml

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

    <FrameLayout
            android:id="@+id/fragment_host"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true">

    </FrameLayout>

    <android.support.design.widget.NavigationView
            android:id="@+id/nav_view"
            android:layout_height="match_parent"
            android:layout_width="wrap_content"
            android:layout_gravity="start"
            android:fitsSystemWindows="true"/>

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

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"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">

    <android.support.design.widget.AppBarLayout
            android:layout_width="match_parent"
            android:layout_height="224dp"
            android:fitsSystemWindows="true"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
...

It worked when activity.xml was this way:

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

    <fragment xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:tools="http://schemas.android.com/tools"
              android:id="@+id/fragment"
              android:name="com.actinarium.random.ui.home.HomeCardsFragment"
              tools:layout="@layout/fragment_home"
              android:layout_width="match_parent"
              android:layout_height="match_parent"/>

    <android.support.design.widget.NavigationView
            android:id="@+id/nav_view"
            android:layout_height="match_parent"
            android:layout_width="wrap_content"
            android:layout_gravity="start"
            android:fitsSystemWindows="true"/>

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

回答1:

When you use <fragment>, the layout returned in your Fragment's onCreateView is directly attached in place of the <fragment> tag (you'll never actually see a <fragment> tag if you look at your View hierarchy.

Therefore in the <fragment> case, you have

DrawerLayout
  CoordinatorLayout
    AppBarLayout
    ...
  NavigationView

Similar to how cheesesquare works. This works because, as explained in this blog post, DrawerLayout and CoordinatorLayout both have different rules on how fitsSystemWindows applies to them - they both use it to inset their child Views, but also call dispatchApplyWindowInsets() on each child, allowing them access to the fitsSystemWindows="true" property.

This is a difference from the default behavior with layouts such as FrameLayout where when you use fitsSystemWindows="true" is consumes all insets, blindly applying padding without informing any child views (that's the 'depth first' part of the blog post).

So when you replace the <fragment> tag with a FrameLayout and FragmentTransactions, your view hierarchy becomes:

DrawerLayout
  FrameLayout
    CoordinatorLayout
      AppBarLayout
      ...
  NavigationView

as the Fragment's view is inserted into the FrameLayout. That View doesn't know anything about passing fitsSystemWindows to child views, so your CoordinatorLayout never gets to see that flag or do its custom behavior.

Fixing the problem is actually fairly simple: replace your FrameLayout with another CoordinatorLayout. This ensures the fitsSystemWindows="true" gets passed onto the newly inflated CoordinatorLayout from the Fragment.

Alternate and equally valid solutions would be to make a custom subclass of FrameLayout and override onApplyWindowInsets() to dispatch to each child (in your case just the one) or use the ViewCompat.setOnApplyWindowInsetsListener() method to intercept the call in code and dispatch from there (no subclass required). Less code is usually the easiest to maintain, so I wouldn't necessarily recommend going these routes over the CoordinatorLayout solution unless you feel strongly about it.

回答2:

My problem was similar to yours: I have a Bottom Bar Navigation which is replacing the content fragments. Now some of the fragments want to draw over the status bar (with CoordinatorLayout, AppBarLayout), others not (with ConstraintLayout, Toolbar).

ConstraintLayout
  FrameLayout
    [the ViewGroup of your choice]
  BottomNavigationView

The suggestion of ianhanniballake to add another CoordinatorLayout layer is not what I want, so I created a custom FrameLayout which handles the insets (like he suggested), and after some time I came upon this solution which really is not much code:

activity_main.xml

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/content"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.example.app.WindowInsetsFrameLayout
        android:id="@+id/fragment_container"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <BottomNavigationView
        android:id="@+id/bottom_navigation"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</android.support.constraint.ConstraintLayout>

WindowInsetsFrameLayout.java

/**
 * FrameLayout which takes care of applying the window insets to child views.
 */
public class WindowInsetsFrameLayout extends FrameLayout {

    public WindowInsetsFrameLayout(Context context) {
        this(context, null);
    }

    public WindowInsetsFrameLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public WindowInsetsFrameLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        // Look for replaced fragments and apply the insets again.
        setOnHierarchyChangeListener(new OnHierarchyChangeListener() {
            @Override
            public void onChildViewAdded(View parent, View child) {
                requestApplyInsets();
            }

            @Override
            public void onChildViewRemoved(View parent, View child) {

            }
        });
    }

}

回答3:

OK, after several people pointing out that fitsSystemWindows works differently, and it should not be used on every view down the hierarchy, I went on experimenting and removing the property from different views.

I got the expected state after removing fitsSystemWindows from every node in activity.xml =\

回答4:

I created this last year to solve this problem: https://gist.github.com/cbeyls/ab6903e103475bd4d51b

Edit: be sure you understand what fitsSystemWindows does first. When you set it on a View it basically means: "put this View and all its children below the status bar and above the navigation bar". It makes no sense to set this attribute on the top container.

回答5:

Another approach written in Kotlin,

The problem:

The FrameLayout you are using does not propagate fitsSystemWindows="true" to his childs:

<FrameLayout
    android:id="@+id/fragment_host"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true" />

A solution:

Extend FrameLayout class and override the function onApplyWindowInsets() to propagate the window insets to attached fragments:

@TargetApi(Build.VERSION_CODES.LOLLIPOP)
class BetterFrameLayout : FrameLayout {

    constructor(context: Context) : super(context)

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs)

    constructor(context: Context, attrs: AttributeSet, defStyle: Int) : super(context, attrs, defStyle)

    override fun onApplyWindowInsets(windowInsets: WindowInsets): WindowInsets {
        childCount.let {
            // propagates window insets to children's
            for (index in 0 until it) {
                getChildAt(index).dispatchApplyWindowInsets(windowInsets)
            }
        }
        return windowInsets
    }
}

Use this layout as a fragment container instead of the standard FrameLayout:

<com.foo.bar.BetterFrameLayout
    android:id="@+id/fragment_host"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true" />

Extra:

If you want to know more about this checkout Chris Banes blog post Becoming a master window fitter.