优化

app/src/main/res/layout/fragment_book_source.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.constraintlayout.widget.ConstraintLayout
+<LinearLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:app="http://schemas.android.com/apk/res-auto"
         android:orientation="vertical"
@@ -11,7 +11,6 @@
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             app:attachToActivity="false"
-            app:layout_constraintTop_toTopOf="parent"
             app:title="@string/book_source"/>
 
     <androidx.recyclerview.widget.RecyclerView
@@ -19,4 +18,4 @@
             android:layout_width="match_parent"
             android:layout_height="match_parent"/>
 
-</androidx.constraintlayout.widget.ConstraintLayout>
+</LinearLayout>

app/src/main/res/layout/fragment_bookshelf.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.constraintlayout.widget.ConstraintLayout
+<LinearLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:app="http://schemas.android.com/apk/res-auto"
         android:orientation="vertical"
@@ -11,7 +11,6 @@
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             app:attachToActivity="false"
-            app:layout_constraintTop_toTopOf="parent"
             app:title="@string/bookshelf"/>
 
-</androidx.constraintlayout.widget.ConstraintLayout>
+</LinearLayout>

app/src/main/res/layout/fragment_find_book.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.constraintlayout.widget.ConstraintLayout
+<LinearLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:app="http://schemas.android.com/apk/res-auto"
         android:orientation="vertical"
@@ -15,4 +15,4 @@
             app:title="@string/find"/>
 
 
-</androidx.constraintlayout.widget.ConstraintLayout>
+</LinearLayout>