Flutter错误： uses-sdk:minSdkVersion 16 cannot be smaller than version 21 declared

前言

今天要做蓝牙通信的功能，我使用了flutter_reactive_ble这个库，但是在运行的时候发现一下错误

Launching lib/main.dart on AQM AL10 in debug mode...

/Users/macbook/Desktop/test/flutter/my_app/android/app/src/debug/AndroidManifest.xml Error:

    uses-sdk:minSdkVersion 16 cannot be smaller than version 21 declared in library [:reactive_ble_mobile] /Users/macbook/Desktop/test/flutter/my_app/build/reactive_ble_mobile/intermediates/merged_manifest/debug/AndroidManifest.xml as the library might be using APIs not available in 16

    Suggestion: use a compatible library with a minSdk of at most 16,

        or increase this project's minSdk version to at least 21,

        or use tools:overrideLibrary="com.signify.hue.flutterreactiveble" to force usage (may lead to runtime failures)

FAILURE: Build failed with an exception.

* What went wrong:

Execution failed for task ':app:processDebugMainManifest'.

> Manifest merger failed : uses-sdk:minSdkVersion 16 cannot be smaller than version 21 declared in library [:reactive_ble_mobile] /Users/macbook/Desktop/test/flutter/my_app/build/reactive_ble_mobile/intermediates/merged_manifest/debug/AndroidManifest.xml as the library might be using APIs not available in 16

    Suggestion: use a compatible library with a minSdk of at most 16,

        or increase this project's minSdk version to at least 21,

        or use tools:overrideLibrary="com.signify.hue.flutterreactiveble" to force usage (may lead to runtime failures)

* 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 4s

┌─ Flutter Fix ─────────────────────────────────────────────────────────────────────────────────┐

│ The plugin reactive_ble_mobile requires a higher Android SDK version.                         │

│ Fix this issue by adding the following to the file                                            │

│ /Users/macbook/Desktop/test/flutter/my_app/android/app/build.gradle:                          │

│ android {                                                                                     │

│   defaultConfig {                                                                             │

│     minSdkVersion 21                                                                          │

│   }                                                                                           │

│ }                                                                                             │

│                                                                                               │

│ Note that your app won't be available to users running Android SDKs below 21.                 │

│ Alternatively, try to find a version of this plugin that supports these lower versions of the │

│ Android SDK.                                                                                  │

│ For more information, see:                                                                    │

│ https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration          │

└───────────────────────────────────────────────────────────────────────────────────────────────┘

Exception: Gradle task assembleDebug failed with exit code 1

Exited

问题原因

自己项目的minSdkVersion比三方SDK的的minSdkVersion低，即版本不一致导致的。

解决办法

方法一

前往项目——>android——>app——>build.gradle文件搜索defaultConfig，将minSdkVersion修改成固定值即可

方法二

进入flutter环境安装目录/packages/flutter_tools/gradle（这里的flutter是环境变量中配置的flutter路径），搜索minSdkVersion，将值改为需求的版本即可（我这里改成21）