idea写Android项目报错Unable to resolve

ERROR: Unable to resolve dependency for ':app@debug/compileClasspath': Could not find any version that matches com.android.support:appcompat-v7:30.+.
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Affected Modules: app


ERROR: Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not find any version that matches com.android.support:appcompat-v7:30.+.
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Affected Modules: app


ERROR: Unable to resolve dependency for ':app@debugUnitTest/compileClasspath': Could not find any version that matches com.android.support:appcompat-v7:30.+.
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Affected Modules: app


ERROR: Unable to resolve dependency for ':app@release/compileClasspath': Could not find any version that matches com.android.support:appcompat-v7:30.+.
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Affected Modules: app


ERROR: Unable to resolve dependency for ':app@releaseUnitTest/compileClasspath': Could not find any version that matches com.android.support:appcompat-v7:30.+.
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Affected Modules: app
 

将代码从

implementation 'com.android.support:appcompat-v7:30.+'


改成

implementation 'com.android.support:appcompat-v7:+'