Trouble with AppcompatActivity - error: cannot find symbol class AppCompatActivity - error-handling

Question

Im using udacity to learn android development and I have ran into a problem. there are a few errors that have come up:
error: package android.v7.app does not exist
error: cannot find symbol class AppCompatActivity
error: method does not override or implement a method from a supertype
error: cannot find symbol variable super
error: cannot find symbol method setContentView(int)
error: cannot find symbol class openNumbersList
error: cannot find symbol method startActivity(Intent)
Everything was working fine but I was following a tutorial and noticed that my imports in my Main Activity didn't match with what was on the tutorial so I changed:
import...
to
import android.v7.app.AppCompatActivity;
import android.os.Bundle;
also even before this, AppCompatActivity was in red:
Main Activity:
package com.example.android.miwok;
import android.content.Intent;
import android.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set the content of the activity to use the activity_main.xml layout file
setContentView(R.layout.activity_main);
}
public void openNumbersList(View view){
Intent i = new Intent(this, openNumbersList.class);
startActivity(i);
}
}
gradle:
apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion '27.0.3'
defaultConfig {
applicationId "com.example.android.miwok"
minSdkVersion 15
targetSdkVersion 23
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'),
'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support.constraint:constraint-layout:1.1.2'
testImplementation 'junit:junit:4.12'
implementation 'com.android.support:appcompat-v7:23.3.0'
implementation 'com.android.support:support-v4:23.3.0'
implementation 'com.android.support:design:23.3.0'
}
hope this helps.

Answer 1

I assume, that you forget to add the dependency to the appcompat support library. Add this to your build.gradle in the app folder:
dependencies {
...
// Add this line
implementation 'artifact com.android.support:appcompat-v7:28.0.0-alpha1'
}
However, you should read other tutorials as well because you will proably face more issues, when you don't know how dependencies work in Android. If you create a fresh project in Android Studio, it will create a runnable app for you which is a good point to start off.
EDIT
I re-read your code and the import is incorrect. It must be
android.support.v7.app.AppCompatActivity
instead of
android.v7.app.AppCompatActivity