Use weak reference to track activity

app/src/main/java/com/topjohnwu/magisk/core/App.kt

@@ -1,6 +1,5 @@
 package com.topjohnwu.magisk.core
 
-import android.annotation.SuppressLint
 import android.app.Activity
 import android.app.Application
 import android.content.Context
@@ -15,6 +14,7 @@ import com.topjohnwu.superuser.internal.UiThreadHandler
 import com.topjohnwu.superuser.ipc.RootService
 import kotlinx.coroutines.Dispatchers
 import timber.log.Timber
+import java.lang.ref.WeakReference
 import kotlin.system.exitProcess
 
 open class App() : Application() {
@@ -81,20 +81,21 @@ open class App() : Application() {
     }
 }
 
-@SuppressLint("StaticFieldLeak")
 object ActivityTracker : Application.ActivityLifecycleCallbacks {
 
+    val foreground: Activity? get() = ref.get()
+
     @Volatile
-    var foreground: Activity? = null
+    private var ref = WeakReference<Activity>(null)
 
     override fun onActivityResumed(activity: Activity) {
         if (activity is SuRequestActivity) return
-        foreground = activity
+        ref = WeakReference(activity)
     }
 
     override fun onActivityPaused(activity: Activity) {
         if (activity is SuRequestActivity) return
-        foreground = null
+        ref.clear()
     }
 
     override fun onActivityCreated(activity: Activity, bundle: Bundle?) {}