Android studio 我在第一次运行颤振项目时收到一个错误`已完成，但出现错误：Gradle任务assembleDebug失败，退出代码为1`

今天我开始学习颤振

我从android studio 3.5.3中的

颤振应用程序创建了新的颤振项目

我创建了新的android虚拟设备，然后尝试运行
main.dart

我记得我的项目在第一次运行时初始化gradle时冻结了，因此我必须停止并重新运行
main.dart
，然后它会引发以下错误：

Launching lib\main.dart on AOSP on IA Emulator in debug mode...
Running Gradle task 'assembleDebug'...

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring root project 'android'.
> Could not resolve all artifacts for configuration ':classpath'.
   > Could not find sdk-common.jar (com.android.tools:sdk-common:26.5.0).
     Searched in the following locations:
         https://dl.google.com/dl/android/maven2/com/android/tools/sdk-common/26.5.0/sdk-common-    26.5.0.jar

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 2s
Finished with error: Gradle task assembleDebug failed with exit code 1

build.gradle
文件包含：

buildscript {
    ext.kotlin_version = '1.3.50'
    repositories {
        google()
        jcenter()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
}

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

include ':app'

def flutterProjectRoot = rootProject.projectDir.parentFile.toPath()

def plugins = new Properties()
def pluginsFile = new File(flutterProjectRoot.toFile(), '.flutter-plugins')
if (pluginsFile.exists()) {
    pluginsFile.withReader('UTF-8') { reader -> plugins.load(reader) }
}

plugins.each { name, path ->
    def pluginDirectory = flutterProjectRoot.resolve(path).resolve('android').toFile()
    include ":$name"
    project(":$name").projectDir = pluginDirectory
}

和
设置。渐变包含：

buildscript {
    ext.kotlin_version = '1.3.50'
    repositories {
        google()
        jcenter()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
}

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

include ':app'

def flutterProjectRoot = rootProject.projectDir.parentFile.toPath()

def plugins = new Properties()
def pluginsFile = new File(flutterProjectRoot.toFile(), '.flutter-plugins')
if (pluginsFile.exists()) {
    pluginsFile.withReader('UTF-8') { reader -> plugins.load(reader) }
}

plugins.each { name, path ->
    def pluginDirectory = flutterProjectRoot.resolve(path).resolve('android').toFile()
    include ":$name"
    project(":$name").projectDir = pluginDirectory
}

我猜冻结是因为初始化的时候连接不好，
sdkcommon.jar
没有正确下载

正如我上面提到的，我对flutter是新手，我不知道如何清理构建项目，所以我一步一步地重复了好几次，但错误仍然存在

我对这个问题一无所知。
有人能帮我吗

如果细节不够清楚，请告诉我


出了什么问题：
配置根项目“android”时出现问题。
无法解析配置“：classpath”的所有项目。
找不到sdk-common.jar（com.android.tools:sdk common:26.5.0）

将maven添加到gradle文件以解决此问题，如下所示

maven { url 'https://maven.google.com' }

尽管我建议您使用API 28

我不知道如何清理和构建这个项目

在项目根文件夹中运行
flatterclean
非常感谢。我在
buildscript
的
repositories
部分添加了它，然后问题就解决了。为什么默认情况下不包括它？