Error:(26, 13) Failed to resolve: com.android.support:appcompat-v7:25.0.1

Starting from version 26 of support libraries make sure that the repositories section includes a maven section with the “https://maven.google.com” endpoint.

在project gradle file -

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

然后同步一下
来源