问题是您传递给 R8 的唯一规则是-dontwarn java.lang.Object. 没有单一-keep规则，这意味着输出将为空，因为没有保留入口点。
缺少的是两组保持规则：
- 适用于所有 Android 应用的一般保留规则
- 具有所有入口点的具体应用程序的特定规则（来自平台的反射访问，例如视图膨胀），可以使用
aapt2.
对于第一组规则，Android Studio（或更准确地说是 AGP）捆绑了这个规则文件，该文件作为getDefaultProguardFile('proguard-android-optimize.txt').
# This is a configuration file for ProGuard.
# http://proguard.sourceforge.net/index.html#manual/usage.html
#
# Starting with version 2.2 of the Android plugin for Gradle, this file is distributed together with
# the plugin and unpacked at build-time. The files in $ANDROID_HOME are no longer maintained and
# will be ignored by new version of the Android plugin for Gradle.
# Optimizations: If you don't want to optimize, use the proguard-android.txt configuration file
# instead of this one, which turns off the optimization flags.
# Adding optimization introduces certain risks, since for example not all optimizations performed by
# ProGuard works on all versions of Dalvik. The following flags turn off various optimizations
# known to have issues, but the list may not be complete or up to date. (The "arithmetic"
# optimization can be used if you are only targeting Android 2.0 or later.) Make sure you test
# thoroughly if you go this route.
-optimizations !code/simplification/arithmetic,!code/simplification/cast,!field/*,!class/merging/*
-optimizationpasses 5
-allowaccessmodification
-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-verbose
# Preserve some attributes that may be required for reflection.
-keepattributes *Annotation*,Signature,InnerClasses,EnclosingMethod
-keep public class com.google.vending.licensing.ILicensingService
-keep public class com.android.vending.licensing.ILicensingService
-keep public class com.google.android.vending.licensing.ILicensingService
-dontnote com.android.vending.licensing.ILicensingService
-dontnote com.google.vending.licensing.ILicensingService
-dontnote com.google.android.vending.licensing.ILicensingService
# For native methods, see http://proguard.sourceforge.net/manual/examples.html#native
-keepclasseswithmembernames,includedescriptorclasses class * {
native <methods>;
}
# Keep setters in Views so that animations can still work.
-keepclassmembers public class * extends android.view.View {
void set*(***);
*** get*();
}
# We want to keep methods in Activity that could be used in the XML attribute onClick.
-keepclassmembers class * extends android.app.Activity {
public void *(android.view.View);
}
# For enumeration classes, see http://proguard.sourceforge.net/manual/examples.html#enumerations
-keepclassmembers enum * {
public static **[] values();
public static ** valueOf(java.lang.String);
}
-keepclassmembers class * implements android.os.Parcelable {
public static final ** CREATOR;
}
# Preserve annotated Javascript interface methods.
-keepclassmembers class * {
@android.webkit.JavascriptInterface <methods>;
}
# The support libraries contains references to newer platform versions.
# Don't warn about those in case this app is linking against an older
# platform version. We know about them, and they are safe.
-dontnote android.support.**
-dontnote androidx.**
-dontwarn android.support.**
-dontwarn androidx.**
# This class is deprecated, but remains for backward compatibility.
-dontwarn android.util.FloatMath
# Understand the @Keep support annotation.
-keep class android.support.annotation.Keep
-keep class androidx.annotation.Keep
-keep @android.support.annotation.Keep class * {*;}
-keep @androidx.annotation.Keep class * {*;}
-keepclasseswithmembers class * {
@android.support.annotation.Keep <methods>;
}
-keepclasseswithmembers class * {
@androidx.annotation.Keep <methods>;
}
-keepclasseswithmembers class * {
@android.support.annotation.Keep <fields>;
}
-keepclasseswithmembers class * {
@androidx.annotation.Keep <fields>;
}
-keepclasseswithmembers class * {
@android.support.annotation.Keep <init>(...);
}
-keepclasseswithmembers class * {
@androidx.annotation.Keep <init>(...);
}
# These classes are duplicated between android.jar and org.apache.http.legacy.jar.
-dontnote org.apache.http.**
-dontnote android.net.http.**
# These classes are duplicated between android.jar and core-lambda-stubs.jar.
-dontnote java.lang.invoke.**
对于第二部分使用aapt2 link选项--proguard。这将生成额外的必需规则，例如：
-keep class com.example.app.MainActivity { <init>(); }
两组规则都必须--pg-conf与附加的应用程序特定规则一起传递给 R8（它可以采用多个选项）。
当使用 Android Studio（更准确地说是 AGP）时，这是自动处理的。作为参考，可以在 中检查这些规则app/build/intermediates/proguard-files。有关更多详细信息，请参阅缩小、混淆和优化您的应用程序。