Launching lib\main.dart on Nokia X6 in debug mode...
Initializing gradle...
Resolving dependencies...
Gradle task 'assembleDebug'...

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:preDebugBuild'.
> Android dependency 'com.android.support:support-v4' has different version for the compile (26.1.0) and runtime (27.1.1) classpath. You should manually set the same version via DependencyResolution

* 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 14s
Finished with error: Gradle task assembleDebug failed with exit code 1

解决方案：

在android/app/build.gradle，dependencies添加一行

dependencies {
    //PART TO ADD

    implementation "com.android.support:support-v4:27.1.1" 
}

网上还有一种方法：

subprojects {

    project.evaluationDependsOn(':app')
    //[PART TO ADD START]
    project.configurations.all {

        resolutionStrategy.eachDependency { details ->

            if (details.requested.group == 'com.android.support'
                    && !details.requested.name.contains('multidex') ) {
                details.useVersion "27.1.0"
            }
        }
    }
    //[PART TO ADD END]
    }