[#101] Improve app startup pre API 26

ui-lib/src/main/java/cash/z/ecc/ui/MainActivity.kt

@@ -2,6 +2,7 @@ package cash.z.ecc.ui
 
 import android.content.ClipData
 import android.content.ClipboardManager
+import android.content.Context
 import android.os.Bundle
 import android.os.SystemClock
 import androidx.activity.ComponentActivity
@@ -10,7 +11,9 @@ import androidx.activity.viewModels
 import androidx.annotation.VisibleForTesting
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.collectAsState
+import androidx.core.content.res.ResourcesCompat
 import androidx.core.splashscreen.SplashScreen.Companion.installSplashScreen
+import androidx.lifecycle.lifecycleScope
 import cash.z.ecc.sdk.model.PersistableWallet
 import cash.z.ecc.ui.screen.backup.view.BackupWallet
 import cash.z.ecc.ui.screen.backup.viewmodel.BackupViewModel
@@ -20,6 +23,10 @@ import cash.z.ecc.ui.screen.home.viewmodel.WalletViewModel
 import cash.z.ecc.ui.screen.onboarding.view.Onboarding
 import cash.z.ecc.ui.screen.onboarding.viewmodel.OnboardingViewModel
 import cash.z.ecc.ui.theme.ZcashTheme
+import cash.z.ecc.ui.util.AndroidApiVersion
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
 import kotlin.time.Duration
 import kotlin.time.Duration.Companion.milliseconds
 import kotlin.time.Duration.Companion.seconds
@@ -36,6 +43,37 @@ class MainActivity : ComponentActivity() {
 
         setupSplashScreen()
 
+        if (AndroidApiVersion.isAtLeastO) {
+            setupUiContent()
+        } else {
+            lifecycleScope.launch {
+                prefetchFontLegacy(applicationContext, R.font.rubik_medium)
+                prefetchFontLegacy(applicationContext, R.font.rubik_regular)
+
+                setupUiContent()
+            }
+        }
+    }
+
+    private fun setupSplashScreen() {
+        installSplashScreen().also {
+            val start = SystemClock.elapsedRealtime().milliseconds
+            it.setKeepVisibleCondition {
+                if (SPLASH_SCREEN_DELAY > Duration.ZERO) {
+                    val now = SystemClock.elapsedRealtime().milliseconds
+
+                    // This delay is for debug purposes only; do not enable for production usage.
+                    if (now - start < SPLASH_SCREEN_DELAY) {
+                        return@setKeepVisibleCondition true
+                    }
+                }
+
+                WalletState.Loading == walletViewModel.state.value
+            }
+        }
+    }
+
+    private fun setupUiContent() {
         setContent {
             ZcashTheme {
                 val walletState = walletViewModel.state.collectAsState().value
@@ -59,24 +97,6 @@ class MainActivity : ComponentActivity() {
         }
     }
 
-    private fun setupSplashScreen() {
-        installSplashScreen().also {
-            val start = SystemClock.elapsedRealtime().milliseconds
-            it.setKeepVisibleCondition {
-                if (SPLASH_SCREEN_DELAY > Duration.ZERO) {
-                    val now = SystemClock.elapsedRealtime().milliseconds
-
-                    // This delay is for debug purposes only; do not enable for production usage.
-                    if (now - start < SPLASH_SCREEN_DELAY) {
-                        return@setKeepVisibleCondition true
-                    }
-                }
-
-                WalletState.Loading == walletViewModel.state.value
-            }
-        }
-    }
-
     @Composable
     private fun WrapBackup(persistableWallet: PersistableWallet) {
         BackupWallet(
@@ -115,3 +135,17 @@ class MainActivity : ComponentActivity() {
         internal val SPLASH_SCREEN_DELAY = 0.seconds
     }
 }
+
+/**
+ * Pre-fetches fonts on Android N (API 25) and below.
+ */
+/*
+ * ResourcesCompat is used implicitly by Compose on older Android versions.
+ * The backwards compatibility library performs disk IO and then
+ * caches the results.  This moves that IO off the main thread, to prevent ANRs and
+ * jank during app startup.
+ */
+private suspend fun prefetchFontLegacy(context: Context, @androidx.annotation.FontRes fontRes: Int) =
+    withContext(Dispatchers.IO) {
+        ResourcesCompat.getFont(context, fontRes)
+    }

ui-lib/src/main/java/cash/z/ecc/ui/util/AndroidApiVersion.kt

@@ -0,0 +1,34 @@
+package cash.z.ecc.ui.util
+
+import android.os.Build
+import androidx.annotation.ChecksSdkIntAtLeast
+import androidx.annotation.IntRange
+
+object AndroidApiVersion {
+    /**
+     * @param sdk SDK version number to test against the current environment.
+     * @return `true` if [android.os.Build.VERSION.SDK_INT] is greater than or equal to
+     * [sdk].
+     */
+    @ChecksSdkIntAtLeast(parameter = 0)
+    fun isAtLeast(@IntRange(from = Build.VERSION_CODES.BASE.toLong()) sdk: Int): Boolean {
+        return Build.VERSION.SDK_INT >= sdk
+    }
+
+    @ChecksSdkIntAtLeast(api = Build.VERSION_CODES.P)
+    val isAtLeastP = isAtLeast(Build.VERSION_CODES.P)
+
+    @ChecksSdkIntAtLeast(api = Build.VERSION_CODES.O)
+    val isAtLeastO = isAtLeast(Build.VERSION_CODES.O)
+
+    @ChecksSdkIntAtLeast(api = Build.VERSION_CODES.Q)
+    val isAtLeastQ = isAtLeast(Build.VERSION_CODES.Q)
+
+    @ChecksSdkIntAtLeast(api = Build.VERSION_CODES.R)
+    val isAtLeastR = isAtLeast(Build.VERSION_CODES.R)
+
+    @ChecksSdkIntAtLeast(api = Build.VERSION_CODES.S)
+    val isAtLeastS = isAtLeast(Build.VERSION_CODES.S)
+
+    val isPreview = 0 != Build.VERSION.PREVIEW_SDK_INT
+}