Create `Debouncer` helper class

1 files changed, 39 insertions, 0 deletions

diff --git a/android/src/main/kotlin/net/mullvad/mullvadvpn/util/Debouncer.kt b/android/src/main/kotlin/net/mullvad/mullvadvpn/util/Debouncer.kt
new file mode 100644
index 0000000000..7afb4c508f
--- /dev/null
+++ b/android/src/main/kotlin/net/mullvad/mullvadvpn/util/Debouncer.kt
@@ -0,0 +1,39 @@
+package net.mullvad.mullvadvpn.util
+
+import kotlin.properties.Delegates.observable
+import kotlinx.coroutines.delay
+
+// Helper to filter out bursts of events so that only the latest event in an interval is notified.
+//
+// An interval of zero means that it will only debounce events that are sent before the job is
+// started. If the events are coming from the UI thread, this means that this class will only send
+// the last event received before the UI thread finishes its current task.
+//
+// This can be used for example to filter out focus events coming from different views. Android will
+// first send a "focus lost" event from a view followed by a "focus gained" event from another view.
+// If the only thing the listener is interested in is if any of a set of views has focus, this class
+// can be used to debounce focus events from the set of views to obtain an event that represents a
+// change from when the set contains a focused view to when the set contains no focused views (and
+// an event for the reverse situation).
+class Debouncer<T>(initialValue: T, val intervalInMs: Long = 0) {
+    private val jobTracker = JobTracker()
+
+    var listener: ((T) -> Unit)? = null
+
+    var debouncedValue = initialValue
+        private set
+
+    var rawValue by observable(initialValue) { _, oldValue, newValue ->
+        if (newValue != oldValue) {
+            jobTracker.cancelJob("notifyNewValue")
+
+            if (newValue != debouncedValue) {
+                jobTracker.newUiJob("notifyNewValue") {
+                    delay(intervalInMs)
+                    listener?.invoke(newValue)
+                    debouncedValue = newValue
+                }
+            }
+        }
+    }
+}