androidStudio3.1.3不能識別constraint-layout預覽佈局的問題

你需要將gradle插件版本升級爲

distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip

dependencies {
    classpath 'com.android.tools.build:gradle:3.1.3'
    

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

implementation 'com.android.support.constraint:constraint-layout:1.1.2'