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I am trying to convert a website to an app and getting this error

This is my first app, I am trying to convert a website to app in android studio. I am following this tutorial - https://youtu.be/oy-0ss-n33g . But I am getting:
Cannot resolve symbol WebView
How can I solve this error?

You forgot to import WebView just add import android.webkit.WebView at the import section or alt + enter to auto-import the class

Import this classes
import android.webkit.WebView;
import android.webkit.WebSettings;
And make sure the ID of the webview in your xml layout is the same as the one you are referring in java.

android.annotation cannot be resolved IntDef and NonNull

I'm trying to run a sample android code in Andriod Studio, but when I try:
import android.annotation.IntDef;
import android.annotation.NonNull;
keep getting an error related to this line like:
the import android.annotation cannot be resolved
Any suggestion will be appreciated

I think it would be better if you work with the support annotations:
add this dependency to your project and see if it works:
compile 'com.android.support:support-annotations:24.2.0'

accourding to this answer you can use
android-sdk/tools/support/annotations.jar - Which includes the following annotations:
SuppressLint
TargetApi
android-sdk/extras/android/support/annotations/annotations.jar - Which includes many other annotations:
AnimRes
AnimatorRes
AnyRes
ArrayRes
AttrRes
BoolRes
ColorRes
DimenRes
DrawableRes
FractionRes
IdRes
IntDef
IntegerRes
InterpolatorRes
LayoutRes
MenuRes
NonNull
Nullable
PluralsRes
RawRes
StringDef
StringRes
StyleRes
StyleableRes
XmlRes

I had faced the same problem and came across this question but was not answered.
I could resolve this issue by following steps mentioned here.
After this, You shall sync the project with Gradle files.
Note: You may not find the same annotation path
e.g. import android.annotation.NonNull; --> import androidx.annotation.Nullable;

Cannot resolve symbol IPAddressUtil

I have a problem in my android studio(macosx) :
in InetAddress.java some import have problem
import sun.net.util.IPAddressUtil;
import android.system.GaiException;
import android.system.StructAddrinfo;
import libcore.io.Libcore;
editor says
cannot resolve symbol IPAddressUtil

I think those classes are not in Android SDK (IpAddressUtil, Libcore). Also, it is discouraged to use classes from sun.* package in your programs.

java.lang.NoSuchMethodError in android

I have include a jar file in my android project. Inside the jar file there is a class OverlayView in a package name android.widget. I can import the class into my Test.java file by import android.widget.OverlayView; and call the method init(). After these I can compile successfully. But while running the app it throws an exception
java.lang.NoSuchMethodError: android.widget.OverlayView.init
I didnt get class definition error

Your library contains android.widget? There is already a package with android.widget as its name. My guess is that it's conflicting with your library. Try deleting the import statements, by this time you should get an error because you deleted the import. Place your cursor in the method that has error then wait for the import suggestion to pop out, then alt+enter to import package. See if it is conflicting with the default android.widget package.

android import error

I am trying use the GPE code for App-Android Android-App communication. Both the two new created folders (Android, AppEngine) have errors. I think the problem is that there are
errors with the packages:
import com.google.web.bindery.requestfactory.shared.InstanceRequest;
import com.google.web.bindery.requestfactory.shared.Request;
import com.google.web.bindery.requestfactory.shared.RequestContext;
import com.google.web.bindery.requestfactory.shared.RequestFactory;
import com.google.web.bindery.requestfactory.shared.ServiceName;
It says "The import com.google.web cannot be resolved." I tried adding everything able to be checked checked in the build path. I also know I installed the Web Toolkit and everything. What is wrong?
Statements like the following also have error markings:
#ProxyForName(value = "com.glm.server.Message",
locator = "com.glm.server.MessageLocator") and actually there are so many errors it must be the imports.