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AppCompatActivity was only added in version 22.1.0 of the support library. Before that it was called ActionBarActivity.

You should use the same version for all of your support libraries. At the time of writing the latest version is 23.1.1 (you can find out the latest here https://developer.android.com/tools/support-library/index.html#revisions) so the dependencies section of your gradle file should look like this.

implementation "com.android.support:support-v4:23.1.1"
implementation "com.android.support:appcompat-v7:23.1.1"
implementation "com.android.support:support-annotations:23.1.1"

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最佳答案

Okay, I fixed it by rebuilding it for doing a ./gradlew clean assemble for the fourth time... Android Studio is a weird thing

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For me, Even after upgrading to appcompat-v7:22.1.0, in which AppCompatActivty is added, the problem was not resolved for me, Android Studio was giving same problem

Cannot resolve symbol 'AppCompatActivity'

Sometimes clearing the android studio caches help.

In android studio I just cleared the caches and restarted with the following option--

File->Invalidate Caches/Restart

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I got the same exact error with In case it helps others .. documenting what worked for me useful for very latest (Jan 14, 2017) latest everything. Tried all the Invalidate, build clean, even deleting .gradle/, tweaking the support libs etc.. on multiple stack overflow answers.

I found that upgrading the settings.gradle gradle version fixed it (it was 2.1.3) something in gradle toolchain seems to classpath 'com.android.tools.build:gradle:2.2.3'

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We don´t need to delete files, just invalidate caches to restart configuration:

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I changed from "... extends ActionBarActivity" to "... extends AppCompatActivity" and tried cleaning, restarting, Invalidate Caches / Restart and wasn't getting anywhere. All my versions were up to the latest.

What finally solved it was making sure my import was correct:

import android.support.v7.app.AppCompatActivity;

For some reason it didn't get set up automatically like I was used to and I had to add it manually.

Hope that helps someone!

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The solution I followed is summarized in the below steps:

From Build menu, select Edit Libraries and Dependancies

Make sure you add the latest AppCompat package if not added

After adding it, clean your project and rebuild it.

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1.Delete the .idea folder
2.Close and reopen the project
3.File - > Sync Project With Gradle Files

This worked for me

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Delete .idea folder in your project which is hidden folder. Goto your project in the system and Click ctrl+H it will be visible then delete it. Now restart your android studio.I will resolve. Its working for me.

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Background info:

My IDE

Android Studio 3.1.3
Build #AI-173.4819257, built on June 4, 2018
JRE: 1.8.0_152-release-1024-b02 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 7 6.1

First solution: Import the project again and don't agree to upgrade the android gradle plug-in.

Second solution: Your files should contain these fragments.

build.gradle:

buildscript {
repositories {
jcenter()
google()//this is important for gradle 4.1 and above
}
dependencies {
classpath 'com.android.tools.build:gradle:3.1.3' //this android plugin for gradle requires gradle version 4.4 and above
}
}
allprojects {
//...
repositories {
jcenter()
google()//This was not added by update IDE-wizard-button.
//I need this when using the latest com.android.support:appcompat-v7:25.4.0 in app/build.gradle
}
}

Either follow the recommendation of your IDE to upgrade your gradle version to 4.4 or consider to have this in gradle/wrapper/gradle-wrapper.properties

distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip

Optional change buildToolsVersion in app/build.gradle:

android {
compileSdkVersion 25
buildToolsVersion '27.0.3'

app/build.gradle: comment out the dependencies and let the build fail (automatically or trigger it)

dependencies {
//compile fileTree(dir: 'libs', include: ['*.jar'])
//compile 'com.android.support:appcompat-v7:25.1.0'
}

app/build.gradle: comment in the dependencies again. It's been advised to change them from compile to implementation, but for now it's just a warning issue.

dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:25.1.0'
}

After project rebuilding, the import statement shouldn't be greyed-out anymore; try to invoke Ctrl+h on the class. But for some reason, the error markers on those class-referencing-statements are still present. To get rid of them, we need to hide and restore the project tree view or alternatively close and reopen the project.

Finally that's it.

Finally found the solution

I tried everything mentioned in all the answers and failed.

Go to gradle.properties make these flags false

android.useAndroidX=false

//Automatically convert third-party libraries to use AndroidX

android.enableJetifier=false

The above flags were

"true ,for me and hence gradle won't download v7 components"

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If you use androidX instead of android, you need change

import android.support.v7.app.AppCompatActivity;

to

import androidx.appcompat.app.AppCompatActivity;

and change

<android.support.constraint.ConstraintLayout>

to

<androidx.constraintlayout.widget.ConstraintLayout>

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File->Invalidate Caches/Restart works for me.

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If the given solutions does not work, create a new project with 'KOTLIN' as the language even if your work is on java. Then replace the 'main' folder of the new project with the 'main' folder of the old.

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androidX users

Change your minSdkVersion to api level 21.

like this minSdkVersion 21 or build your app with compileSdkVersion 28 and also change targetSdkVersion to targetSdkVersion 28

and you will see v7 error will gone. After that if you face a problem with creating Toolbar or other widget. press Alt+Enter and create a method for it.

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Replace the

import android.support.v7.app.AppCompatActivity;

with import androidx.appcompat.app.AppCompatActivity

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I had these settings in 'gradle.properties'

android.useAndroidX=true # Automatically convert third-party libraries to use AndroidX android.enableJetifier=true

It is better to use androidx library. So I changed all imports to androidx library and project compiled. visit http://developer.android.com/jetpack/androidx for information.

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The issue could be import reference,
try changing it. From:

import android.support.v7.app.AppCompatActivity;

To:

import androidx.appcompat.app.AppCompatActivity;

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I went through the same situation and the fix was quiet easy. Just try removing the following import statement.

import android.support.v7.app.AppCompatActivity;

A message will be prompted with the below code, also asking you to press alt+enter.

import androidx.appcompat.app.AppCompatActivity;

Just press alt+enter and remove the previous import statement completely.

Basically this problem arises in new version of Android Studio.

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For me, the below code worked well:

import android.os.Bundle;


import androidx.appcompat.app.AppCompatActivity;

With the (xml file):

androidx.constraintlayout.widget.ConstraintLayout xmlns:android="...."

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I just commented it and used androidx and now it's working all good!

import androidx.appcompat.app.AppCompatActivity;
// import android.support.v7.app.AppCompatActivity;

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After invalidating Cache, changing from

import android.support.v7.app.AppCompatActivity;

to

import androidx.appcompat.app.AppCompatActivity;

worked for me.

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Include import androidx.appcompat.app.AppCompatActivity; in your MainActivity.java with other import statements. This would look like:

this resolved my issue

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Follow these steps:


File >> Invalidate Caches / Restart
Clean project
Finally go to build.gradle
And compileSdkVersion and targetSdkVersion lower version
If
implementation 'com.android.support:appcompat-v7:29.0.0'
Convert this to
implementation 'com.android.support:appcompat-v7:28.0.0'

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Support V7 AppCompat requires compatible Gradle Version as below,

its work for me

无法解析无法识别 AppCompatActivity-Supportv7库的符号？

Finally found the solution