Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
刚安装的Android studio 3.2.1 build 出现问题
已经解决：
1.下载比出现问题的gradle版本高的版本，我的出现问题是4.6-all.zip，然后在https://services.gradle.org/distributions/ 下载了 grale-5.0-all.zip
2.解压5.0-all.zip到自己制定的文件夹下。
3.修改路径为->gradle home： C:/Users/XXXX/AppData/Local/Android/gradle-5.0，选中 use local gradle distribution
4.修改Maven
5.然后再build 
6. 报错
Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
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Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.3.
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.........
7. update IDE
"File"->"Invalidate Caches / Restart ..."
8.进行 5.然后再build 
还是报错 Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support:appcompat-v7:28.0.0.
....
网上查找方法都是设置 offline work，但还是没有解决。
File -> Settings -> Build, Execution, Deployment -> Gradle menu. You will see "Offline work"
但是可以使用Run了，以后再补充吧
9. 点击Run
Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.3.
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Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve com.android.support.test:runner:1.0.2.
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Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve com.android.support.test.espresso:espresso-core:3.0.2.
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修改 App -> build.gradle, 修改appcompat-v7:21.0.0'版本，先将报错的项目注释掉，再build。
dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
testImplementation 'com.android.support.constraint:constraint-layout:1.1.3'
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'
implementation 'com.android.support:appcompat-v7:21.0.0'
// implementation 'com.android.support.constraint:constraint-layout:1.1.3'
//implementation 'com.android.support.test:runner:1.0.2'
//implementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}
/**/