activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout
  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"
  tools:context="link.k3n.bottom_sheet_behavior_sample.MainActivity">

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

    <!--BottomSheetBehaviorのpeekHeight分だけ高さを縮める-->
    <RelativeLayout
      android:id="@+id/contents_root_layout"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_marginBottom="50dp">

      <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:text="Hello World!"/>

    </RelativeLayout>

    <RelativeLayout
      android:id="@+id/bottom_sheet_behavior_root_layout"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:background="#FFFFFFFF"
      app:layout_behavior="link.k3n.bottom_sheet_behavior_sample.LockableBottomSheetBehavior"
      app:behavior_peekHeight="50dp"
      app:behavior_hideable="false">

      <LinearLayout
        android:id="@+id/bottom_sheet_behavior_bar_root_layout"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:orientation="horizontal">

        <ImageButton
          android:id="@+id/bottom_sheet_behavior_toggle_button"
          android:layout_width="24dp"
          android:layout_height="24dp"
          android:layout_marginStart="8dp"
          android:layout_gravity="center_vertical"
          android:background="@mipmap/ic_launcher"
          android:clickable="true"
          android:focusable="true"
          tools:ignore="ContentDescription"/>

        <TextView
          android:id="@+id/bottom_sheet_behavior_status_text"
          android:layout_width="0dp"
          android:layout_height="match_parent"
          android:layout_weight="1"
          android:textColor="#4c4c4c"
          android:textSize="28sp"
          android:gravity="center"
          android:text="Collapse"/>

      </LinearLayout>

      <LinearLayout
        android:id="@+id/bottom_sheet_behavior_contents_root_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/bottom_sheet_behavior_bar_root_layout"
        android:layout_above="@id/bottom_sheet_behavior_edit_text_root_layout"
        android:orientation="vertical">

        <TextView
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:gravity="center"
          android:textSize="14sp"
          android:textColor="#808080"
          android:text="Hello World!"/>

      </LinearLayout>

      <FrameLayout
        android:id="@+id/bottom_sheet_behavior_edit_text_root_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true">

        <EditText
          android:id="@+id/bottom_sheet_behavior_edit_text"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:paddingEnd="40dp"
          android:textSize="14sp"
          android:textColor="#4c4c4c"
          android:textColorHint="#808080"
          android:maxLines="3"
          android:inputType="textMultiLine"
          android:hint="Input text here!"
          tools:ignore="LabelFor"/>

        <ImageButton
          android:id="@+id/bottom_sheet_behavior_clear_button"
          android:layout_width="25dp"
          android:layout_height="25dp"
          android:layout_gravity="center_vertical|end"
          android:layout_marginEnd="35dp"
          android:background="@mipmap/ic_launcher_round"
          android:foreground="?android:selectableItemBackgroundBorderless"
          tools:ignore="ContentDescription"/>

        <ImageButton
          android:id="@+id/bottom_sheet_behavior_send_button"
          android:layout_width="25dp"
          android:layout_height="25dp"
          android:layout_gravity="center_vertical|end"
          android:layout_marginEnd="5dp"
          android:background="@mipmap/ic_launcher_round"
          android:foreground="?android:selectableItemBackgroundBorderless"
          tools:ignore="ContentDescription"/>

      </FrameLayout>

    </RelativeLayout>

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

</layout>