App Bar is not showing in Android Studio but showing on an actual android device - android-studio

Question

I have already checked similar problems like mine but none of it helped. I also checked my previous project with the same AppTheme, they are the same but I have noticed everytime I create a new android project, the App bar is not showing even after several "Rebuild Project".
This is what my styles.xml shows
<resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- Customize your theme here. -->
<item name="colorPrimary">#color/colorPrimary</item>
<item name="colorPrimaryDark">#color/colorPrimaryDark</item>
<item name="colorAccent">#color/colorAccent</item>
</style>
</resources>
This is what my AndroidManifest.xml shows
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.mycontact">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
My MainActivity.java (Haven't put code yet)
package com.example.mycontact;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
And my activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
tools:context=".MainActivity"
android:orientation="vertical">
</LinearLayout>
I have also tried changing the layout from ContraintLayout, RelativeLayout but nothing has changed. Zooming in and zooming out the layout doesn't change at all. Here is a snapchat.. Thank you for your help.
activity_main.xml page

Answer 1

Your styles.xml and other files seem to be in order, so try the following out.
Click the "Eye" icon on the toolbar above the XML Layout Preview, and then select "Show Layout Decorations" if it is unchecked. This should make it display both the AppBar and the system navigation bar.
Screenshots for reference, taken on Android Studio 3.3:
1. Layout with decorations missing
2. Press the 'Eye' icon, and select the option
3. The decorations (AppBar and system navigation bar) should now be visible