Floating action button issue when going to another

问题:

I built a project based on Scrolling Activity (pre-built activity suggested by android studio) and faced a strange issue. Consider the following scenario:

I clicked on fab button to go to another fragment but when the fragment changed, the fab button is not disappeared!

Can anybody know how to fix this problem?

Here is my XML of Scrolling Activity that I added to my frameLayout:

    <?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="ir.apio.myapplication.ScrollingActivity">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_width="match_parent"
        android:layout_height="@dimen/app_bar_height"
        android:fitsSystemWindows="true"
        android:theme="@style/AppTheme.AppBarOverlay">

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

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

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

    <include layout="@layout/content_scrolling" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/fab_margin"
        android:src="@android:drawable/ic_dialog_email"
        app:layout_anchor="@id/app_bar"
        app:layout_anchorGravity="bottom|end" />


    <FrameLayout
        android:id="@+id/frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</android.support.design.widget.CoordinatorLayout>

content_scrolling.xml :

    <?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.NestedScrollView 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:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="ir.apio.myapplication.ScrollingActivity"
    tools:showIn="@layout/activity_scrolling">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/text_margin"
        android:text="@string/large_text" />

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

My fab ClickListener :

fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                getSupportFragmentManager()
                        .beginTransaction()
                        .replace(R.id.frame,new TestFragment())
                        .commit();
            }
        });

And also my TestFragment :

public static class TestFragment extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_test,container,false);
            return view;
        }
    }

Here is screen-shot before going to new fragment

Here is screen-shot when going to new fragment

回答1:

The reason you are still seeing the FAB is elevation, which refers to a views depth on the screen. It affects which elements are above or below one another and the shadows they cast(for example a FAB sits on top of the main content and casts a shadow).

The FAB by default will have some elevation, which you can override using the elevation attribute, eg app:elevation="4dp". The other elements will be at the 0dp level.

In your case, you've put the FrameLayout last in your layout file, and I presume that's where you are loading your fragment into. What this does is not actually replace your other content, but just cover it with the content of your FrameLayout.

The reason it doesn't cover the FAB, is because the FAB has some elevation and the FrameLayout doesn't. So although you've put your FrameLayout last and would normally expect that to be "on top", the FAB actually has a higher elevation which overrides that.

A quick fix, would be to give your floating action button app:elevation=0dp which would put it back on the same elevation level as everything else and the normal rules would apply, the FrameLayout is last and would be on top.

In reality, just putting a big frame covering the previous content is not usually the best thing to do and you would want to look at other ways to structure the app.

回答2:

I had the same problem. I called the .hide() method on the FragmentTransaction and it worked for me.

fab.setOnClickListener {
        val fragmentManager = fragmentManager
        val fragmentTransaction = fragmentManager?.beginTransaction()
        val fragment = YourFragment()
        fragmentTransaction?.add(R.id.fragment_container, fragment)
        fragmentTransaction?.addToBackStack(null)
        fragmentTransaction?.hide(this)
        fragmentTransaction?.commit()
    }