Multi tool use

I couldn't make my first app

So, beginner here and I have a problem with dropping the plain text widget into the layout. Here is a screenshot.

I cannot constrain the widget because the widget does not even show. I looked at various tutorials on how to bypass that but I have been unsuccessful. You may see that there is a render problem, missing accessibility label and failed to instantiate one or more classes3. So, my question is, why is widget not showing and does it have to with the 3 messages that android studio threw at me?

Edit 1:
Mandatory: Based on the second answer I changed this code: "Theme.AppCompat.Light.DarkActionBar" into this one: "base.Theme.AppCompat.Light.DarkActionBar". With the second solution, I was able to drop my widgets into the layout screen. This is why I say that the answer half-helped me because I got forward with my project but lost my 'design' feature(the one alongside the 'blueprint'). Here are some photos that may help you understand my problem:

strings.xml

AndroidManifest.xml

MainActivity.java

As you can see, I don't have the design feature:

Render Problem:

Missing Constraints:

Missing Styles
Missing Styles

2 Answers
2

Try to use same version in gradle compileSdkVersion, buildToolsVersion, and supportLibraryFunction

compileSdkVersion

buildToolsVersion

supportLibraryFunction

Also check in project file of gradle has

dependencies {
classpath 'com.android.tools.build:gradle:3.0.0'
}


Hope this helps for you.

compileSdkVersion

targetSdkVersion

dependencies

compileSdkVersion 27

targetSdkVersion 27

implementation 'com.android.support:appcompat-v7:27.1.1'

First of all, welcome to the Android Community.
Now, regarding your error, here are few possible solutions which might work:-

If the above solution does not work

I hope this helps.

EDIT:
Change the styles.xml as follows:-

<!-- Base application theme. -->
<style name="AppTheme" parent="Base.Theme.AppCompat.Light.DarkActionBar">
<item name="colorPrimary">@color/primary_color</item>
<item name="colorPrimaryDark">@color/primary_dark_color</item>
</style>


There was a typo, b in Base should be capital

I hope this edit helps.

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