docs/docs-android/app/src/main/res/layout/login_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_gravity="center"
    android:gravity="center"
    android:orientation="vertical"
    android:background="@color/colorPrimaryDark">

    <LinearLayout
        android:id="@+id/loginForm"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:visibility="visible"
        android:padding="40dp"
        android:orientation="vertical">

        <ImageView
            android:contentDescription="@string/app_name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@mipmap/ic_launcher"
            android:layout_marginBottom="20dp" />

        <TextView
            android:id="@+id/loginExplain"
            android:gravity="center"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

        <EditText
            android:id="@+id/txtServer"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="0.5"
            android:ems="10"
            android:hint="@string/server"
            android:inputType="textNoSuggestions">
        </EditText>

        <EditText
            android:id="@+id/txtUsername"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="0.5"
            android:ems="10"
            android:hint="@string/username"
            android:inputType="textNoSuggestions">

            <requestFocus />
        </EditText>

        <EditText
            android:id="@+id/txtPassword"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="0.5"
            android:ems="10"
            android:hint="@string/password"
            android:inputType="textPassword">
        </EditText>

        <EditText
            android:visibility="gone"
            android:id="@+id/txtValidationCode"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="0.5"
            android:ems="10"
            android:hint="@string/validation_code"
            android:inputType="number">
        </EditText>

        <Button
            android:id="@+id/btnConnect"
            android:layout_width="fill_parent"
            android:layout_height="50dip"
            android:layout_marginTop="20dip"
            android:gravity="center"
            android:text="@string/login" />
    </LinearLayout>

    <LinearLayout
        android:id="@+id/progressBar"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:gravity="center"
        android:visibility="gone">

        <ProgressBar
            style="?android:attr/progressBarStyleLarge"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:indeterminate="false" />
    </LinearLayout>

</LinearLayout>