Unable to resolve all dependencies in android studio [duplicate]

Answer 1

I think that you are missing the Google maven repo.

repositories {
    jcenter()
    maven {
        url "https://maven.google.com"
    }
}

You have the full document here.

Answer 2

Change your compile 'com.android.support:appcompat-v7:26.1.0'

To this

implementation 'com.android.support:support-compat:27.0.0'

You'll need the gradle version 3.0.0 to use implementation, on your project level build.gradle you should change

buildscript {
    repositories {
        ...
        // You need to add the following repository to download the
        // new plugin.
        google()
    }

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