gradle error

ERROR: In <declare-styleable> FontFamilyFont, unable to find attribute android:fontVariationSettings
ERROR: In <declare-styleable> FontFamilyFont, unable to find attribute android:ttcIndex


 FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':processDebugResources'.
> com.android.ide.common.process.ProcessException: Failed to execute apt

在build.gradle中添加以下即可

configurations.all {
  resolutionStrategy {
    force 'com.android.support:support-v4:27.1.0'
  }
}

或者
linphone-android 内build.gradle的第51行

compile 'com.android.support:support-v4:+'
-->
compile 'com.android.support:support-v4:27.1.0'

参考文章
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参考3