构建项目时依赖库下载不下来的解决

在项目级build.gradle的两个repositories中加上这几段代码，再开着代0理，就可以了。

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        maven { url "https://maven.aliyun.com/repository/google" }
        maven { url "https://maven.aliyun.com/repository/jcenter" }
        maven { url "https://maven.aliyun.com/repository/public" }
        maven { url "https://jitpack.io" }
        google()
        jcenter()

    }
    dependencies {
        classpath 'com.android.tools.build:gradle:4.0.1'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        maven { url "https://maven.aliyun.com/repository/google" }
        maven { url "https://maven.aliyun.com/repository/jcenter" }
        maven { url "https://maven.aliyun.com/repository/public" }
        maven { url "https://jitpack.io" }
        google()
        jcenter()

    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}