android tools:showin,xml - tools:showIn causing error in Android layout - Stack Overflow

I've searched through the site but haven't found a similar question. I have finished making this layout, and then I proceeded to make some changes in my code (not regarding the layout), and when I came back to content_main.xml, the layout decided not to render. The solution seems to be when I remove this line:

tools:showIn="@layout/activity_main"

Then the layout renders, of course, without the toolbar. The layout is slightly complicated, but it worked fine up until now, and I haven't changed anything in the toolbar layout. Where should I look? In the content_main.xml,activity_main, or where? Also, I can post whatever piece of code might be relevant to this problem. But I do not know what is relevant and what isn't, so instead of posting 500 xml lines of code, (plus 2600 lines in java), I'm not going to post until someone tells me what might be the problem.

EDIT

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:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

app:layout_behavior="@string/appbar_scrolling_view_behavior"

tools:context="com.example.samprocreativecenter.nfc.MainActivity"

android:orientation="horizontal"

android:background="#819fba">

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:orientation="vertical">

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:orientation="vertical"

android:background="@drawable/ekran"

android:clickable="false">

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:gravity="end"

android:id="@+id/txtStatus"

android:textColor="#ffffff"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="3"

android:textSize="28sp"

android:textColor="#ffffff"

android:id="@+id/editUnos"

android:fontFamily="sans-serif-thin"

android:gravity="bottom|end"

/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="2"

android:id="@+id/layoutTasteri"

android:orientation="vertical">

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img1"

android:src="@drawable/p1"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img2"

android:src="@drawable/p2"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img3"

android:src="@drawable/p3"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img4"

android:src="@drawable/p4"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img5"

android:src="@drawable/p5"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img6"

android:src="@drawable/p6"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img7"

android:src="@drawable/p7"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img8"

android:src="@drawable/p8"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img9"

android:src="@drawable/p9"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/imgNazad"

android:src="@drawable/delete"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/img0"

android:src="@drawable/p0"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/imgEnter"

android:src="@drawable/enter"/>

android:layout_width="30dp"

android:layout_height="match_parent"

android:src="@drawable/linija"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:visibility="gone"

android:id="@+id/layoutOtvorenListView"

android:orientation="vertical">

android:layout_width="match_parent"

android:layout_height="18dp"

android:id="@+id/txtSmanjiListView"

android:background="#607b9a"

android:text="Info panel"

android:textColor="#d9e8e7"/>

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:id="@+id/listViewOtvoreni"

android:stackFromBottom="true">

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:orientation="vertical"

android:id="@+id/layoutSredina">

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:orientation="vertical">

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:gravity="center"

android:textSize="60sp"

android:id="@+id/textClock"

android:textColor="#ffffff"/>

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:textSize="27sp"

android:id="@+id/txtDatum"

android:gravity="center"

android:textColor="#ffffff"

android:fontFamily="sans-serif-thin"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:orientation="vertical"

android:id="@+id/layoutSredinaPodesavanja"

android:visibility="gone"

>

android:layout_width="match_parent"

android:layout_height="match_parent"

android:id="@+id/imgUspesnaVerifikacija"

/>

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentStart="true"

android:text="Domen"

android:id="@+id/domen"

android:textColor="#ffffff"

android:textSize="12sp"/>

android:layout_below="@+id/domen"

android:layout_marginTop="2dp"

android:layout_width="match_parent"

android:layout_height="27dp"

android:textColor="#ffffff"

android:background="@drawable/unos_polje_neaktivno"

android:textColorHint="#a6bbce"

android:singleLine="true"

android:maxLines="1"

android:id="@+id/editDomen"/>

android:layout_below="@+id/editDomen"

android:layout_marginTop="12dp"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:id="@+id/server"

android:text="Adresa servera"

android:textColor="#ffffff"

android:textSize="12sp"/>

android:layout_below="@+id/server"

android:layout_marginTop="2dp"

android:layout_width="match_parent"

android:layout_height="27dp"

android:background="@drawable/unos_polje_neaktivno"

android:textColor="#ffffff"

android:maxLines="1"

android:textColorHint="#a6bbce"

android:id="@+id/editServer"/>

android:layout_width="100dp"

android:layout_height="40dp"

android:layout_gravity="end"

android:id="@+id/imgVerifikacija"

android:src="@drawable/verifikacija"

android:layout_alignParentBottom="true"

android:layout_alignParentEnd="true"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1.7"

android:orientation="vertical"

android:id="@+id/layoutSredinaDole"

android:visibility="visible">

android:layout_width="0dp"

android:layout_height="0dp"

android:id="@+id/spnMestoTroska"

android:spinnerMode="dropdown"

android:layout_gravity="start"

>

android:layout_width="120dp"

android:layout_height="70dp"

android:layout_gravity="center"

android:background="@drawable/mesto_troska"

android:id="@+id/txtSpinner"

/>

android:layout_width="match_parent"

android:layout_height="18dp"

android:background="@drawable/rsz_prologin_pocetna_1"

android:id="@+id/txtListView"/>

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:id="@+id/listView">

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:orientation="vertical"

android:id="@+id/layoutDesniPodesavanja"

android:visibility="gone"

>

android:layout_marginTop="20dp"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginStart="10dp"

android:text="Rezim sinhronizacije"

android:textSize="13sp"

android:textColor="#a6bbce"

android:id="@+id/rezim"/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginStart="10dp"

android:textSize="13sp"

android:textColor="#ffffff"

android:id="@+id/txtSinhronizacija"

android:layout_below="@+id/rezim"/>

android:layout_marginStart="5dp"

android:layout_width="55dp"

android:layout_height="40dp"

android:layout_alignParentEnd="true"

android:layout_alignTop="@+id/rezim"

android:id="@+id/imgSinhronizuj"

android:src="@drawable/sinhronizuj"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:textColor="#ffffff"

android:singleLine="true"

android:layout_below="@+id/imgSinhronizuj"

android:textSize="9sp"

android:text="Sinhronizuj"

android:layout_alignStart="@+id/imgSinhronizuj"

android:layout_marginStart="8dp"

android:id="@+id/sinhronizuj"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Rezim rada terminala:"

android:textColor="#a6bbce"

android:layout_marginStart="10dp"

android:textSize="13sp"

android:layout_below="@+id/sinhronizuj"

android:layout_marginTop="15dp"

android:id="@+id/rezimrada"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/txtTipRV"

android:layout_below="@+id/rezimrada"

android:layout_alignStart="@+id/rezimrada"

android:layout_marginStart="10dp"

android:textColor="#ffffff"

/>

android:layout_width="55dp"

android:layout_height="50dp"

android:layout_alignParentBottom="true"

android:layout_alignParentEnd="true"

android:layout_marginEnd="15dp"

android:layout_marginBottom="15dp"

android:id="@+id/imgOdustani"

android:src="@drawable/odustani" />

android:layout_width="55dp"

android:layout_height="50dp"

android:layout_alignParentBottom="true"

android:layout_alignParentStart="true"

android:layout_marginBottom="15dp"

android:layout_marginStart="15dp"

android:id="@+id/imgSacuvaj"

android:src="@drawable/snimi"/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/txtKoristiMT"

android:layout_below="@+id/txtTipRV"

android:layout_alignStart="@+id/txtTipRV"

android:textColor="#ffffff"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/txtGPS"

android:layout_below="@+id/txtKoristiMT"

android:layout_alignStart="@+id/txtKoristiMT"

android:textColor="#ffffff"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/txtSlika"

android:layout_below="@+id/txtGPS"

android:layout_alignStart="@+id/txtGPS"

android:textColor="#ffffff"

/>

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/txtDozTestaturu"

android:layout_below="@+id/txtSlika"

android:layout_alignStart="@+id/txtSlika"

android:textColor="#ffffff"

/>

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:orientation="vertical"

android:id="@+id/layoutDesni"

android:visibility="visible">

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="0.9">

android:layout_width="0dp"

android:layout_weight="1"

android:layout_height="match_parent"

android:id="@+id/imgDolazak"

android:src="@drawable/dolazak"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/imgOdlazak"

android:src="@drawable/odlazak"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="0.6">

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/imgPauza"

android:src="@drawable/pauza"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/imgTeren"

android:src="@drawable/rad_teren"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="1"

android:id="@+id/imgPrivatno"

android:src="@drawable/privatno"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="0.3">

android:layout_width="0dp"

android:layout_height="wrap_content"

android:layout_weight="1"

android:text="Pauza"

android:textColor="#ffffff"

android:textSize="10sp"

android:src="@drawable/pauza"

android:gravity="center"/>

android:layout_width="0dp"

android:layout_height="wrap_content"

android:layout_weight="1"

android:src="@drawable/rad_teren"

android:text="Rad na terenu"

android:gravity="center"

android:textColor="#ffffff"

android:textSize="10sp"/>

android:layout_width="0dp"

android:layout_height="wrap_content"

android:layout_weight="1"

android:src="@drawable/privatno"

android:text="Privatno odsutan"

android:gravity="center"

android:textColor="#ffffff"

android:textSize="10sp"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1.17">

android:layout_width="match_parent"

android:layout_height="match_parent">

android:layout_width="70dp"

android:layout_height="match_parent"

android:scaleType="centerCrop"

android:id="@+id/imgView"

android:layout_marginStart="5dp"/>

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

android:layout_marginStart="1dp">

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:textColor="#a6bbce"

android:text="Poslednji prijavljeni"

android:textSize="12sp"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:id="@+id/txtPoslenjiUpisani"

android:textColor="#ffffff"

android:text=""

android:textSize="12sp"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:textColor="#a6bbce"

android:text="Pozicija"

android:textSize="12sp"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:id="@+id/txtPoslednjeMestoTroska"

android:textColor="#ffffff"

android:text=""

android:textSize="12sp"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:textColor="#a6bbce"

android:text="Vreme"

android:textSize="12sp"/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1"

android:textColor="#ffffff"

android:id="@+id/txtPoslenjeVreme"

android:text=""

android:textSize="12sp"/>

android:layout_width="0.1dp"

android:layout_height="0.1dp"

android:id="@+id/texture"

android:layout_gravity="center"

/>

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="0.6"

android:layout_marginTop="4dp">

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="0.9"

android:id="@+id/imgScrollLevo"

android:src="@drawable/levo"/>

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_marginTop="1dp"

android:layout_weight="5"

android:id="@+id/horScrollView"

android:gravity="center">

android:layout_width="wrap_content"

android:layout_height="match_parent"

android:gravity="center"

android:id="@+id/layoutZaposleni"

android:orientation="horizontal">

android:layout_width="0dp"

android:layout_height="match_parent"

android:layout_weight="0.9"

android:id="@+id/imgScrollDesno"

android:src="@drawable/desno"/>

And yes, I am aware that nested weights can be an issue, but this is still a test build. All the drawables exist and work.