I have been getting unable to resolve dependencies error after updating the gradle to 5.1.1. I have tried all the possible solutions in this thread and this one as well. But couldn't fix my problem.
This is my error log :
Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.3.
Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support:design:28.0.0.
Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve com.android.support.test:runner:1.0.2.
Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve com.android.support.test.espresso:espresso-core:3.0.2.
Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.3.
Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve com.android.support:design:28.0.0.
Unable to resolve dependency for ':app@debugUnitTest/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
Unable to resolve dependency for ':app@debugUnitTest/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.3.
Unable to resolve dependency for ':app@debugUnitTest/compileClasspath': Could not resolve com.android.support:design:28.0.0.
Unable to resolve dependency for ':app@release/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
Unable to resolve dependency for ':app@release/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.3.
Unable to resolve dependency for ':app@release/compileClasspath': Could not resolve com.android.support:design:28.0.0.
Unable to resolve dependency for ':app@releaseUnitTest/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
Unable to resolve dependency for ':app@releaseUnitTest/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.3.
Unable to resolve dependency for ':app@releaseUnitTest/compileClasspath': Could not resolve com.android.support:design:28.0.0.
And this is app level build.gradle file
apply plugin: 'com.android.application'
android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.project.FirstApplication"
        minSdkVersion 15
        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'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:design:28.0.0'
    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'
}
This is project's build.gradle
buildscript {
    repositories {
        google()
        jcenter()
        maven {
            url "https://maven.google.com"
        }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.1'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}
allprojects {
    repositories {
        google()
        jcenter()
        maven {
            url "https://maven.google.com"
        }
    }
}
task clean(type: Delete) {
    delete rootProject.buildDir
}
Regards
 
     
    