Android build prompt "Could not resolve all files for configuration ':app:debugRuntimeClasspath'."

When adding the MQTT dependency library today, an error was prompted during the build:

Caused by: org.gradle.api.internal.artifacts.ivyservice.DefaultLenientConfiguration$ArtifactResolveException: Could not resolve all files for configuration ':app:debugRuntimeClasspath'.

Later, according to the wrong prompt, it may be related to the sentence added in build.gradle(:app) in the project:

implementation 'com.android.support:support-v4:4.4.1'

I checked some information on the Internet, and finally found that it was because I used the Androidx library when creating a new project in Android Studio. If the third-party dependency library used at this time contains the old version of the Support library, it will cause conflicts and errors.

The solution is also relatively simple, that is, add a sentence to the gradle.properties file in the project:

android.enableJetifier=true

 In this way, the file contains both android.useAndroidX=true and android.enableJetifier=true. Let's analyze the understanding of these two sentences:

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• android.useAndroidX: true When , the Android plugin uses the corresponding AndroidX library instead of the support library. If not specified, this flag defaults to  false.
• android.enableJetifier: true When , the Android plugin automatically migrates existing third-party libraries to use AndroidX dependencies by rewriting their binaries. If not specified, this flag defaults to  false.

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 There is a detailed introduction on the official website of Android, please refer to: AndroidX Overview | Android Developers | Android Developers (google.cn) https://developer.android.google.cn/jetpack/androidx