title: Elements are invisible in GridLayout
body: <p>Any elements I put in the GridLayout, they become invisible in the preview window inside activity_main. When I run the app, the element appears where it should in the emulator, but not in the activity_main preview mode.
  I'm guessing it's an attribute setting for GridLayout, but I'm not sure where to look. </p>
  
  <p><a href="https://i.stack.imgur.com/l4JgC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/l4JgC.png" alt="enter image description here"></a></p>
  
  <p>activity_main.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.constraint.ConstraintLayout 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"&gt;
  
      &lt;android.support.v7.widget.GridLayout
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"&gt;
  
          &lt;Button
              android:id="@+id/button10"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:layout_weight="1"
              android:text="@string/btnText"
              app:layout_column="30"
              app:layout_row="0" /&gt;
      &lt;/android.support.v7.widget.GridLayout&gt;
  
      &lt;LinearLayout
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="horizontal"&gt;
  
      &lt;/LinearLayout&gt;
  
  &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>
  
  <p>Also I noticed this error from the StackTrace</p>
  
  <p><a href="https://i.stack.imgur.com/nYfNk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nYfNk.png" alt="enter image description here"></a></p>
  
  <p>Here's the build.gradle requested. I wasn't sure which one you wanted so here's both.</p>
  
  <pre><code>// Top-level build file where you can add configuration options common to all sub-projects/modules.
  
  buildscript {
  
      repositories {
          google()
          jcenter()
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:3.1.4'
  
  
          // NOTE: Do not place your application dependencies here; they belong
          // in the individual module build.gradle files
      }
  }
  
  allprojects {
      repositories {
          google()
          jcenter()
      }
  }
  
  task clean(type: Delete) {
      delete rootProject.buildDir
  }
  </code></pre>
  
  <hr>
  
  <pre><code>apply plugin: 'com.android.application'
  
  android {
      compileSdkVersion 28
      defaultConfig {
          applicationId "com.example.annovak.gridlayout"
          minSdkVersion 26
          targetSdkVersion 28
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      implementation fileTree(dir: 'libs', include: ['*.jar'])
      implementation 'com.android.support:appcompat-v7:28.0.0-rc01'
      implementation 'com.android.support.constraint:constraint-layout:1.1.2'
      testImplementation 'junit:junit:4.12'
      androidTestImplementation 'com.android.support.test:runner:1.0.2'
      androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
      implementation 'com.android.support:gridlayout-v7:28.0.0-rc01'
  }
  </code></pre>