refresh borders of sentences

android/oral-trainer-sdk/src/main/java/cn/learningpad/oraltrainer/sdk/OralTrainerController.kt

@@ -141,6 +141,28 @@ class OralTrainerController internal constructor(
         loadItems(listOf(item))
     }
 
+    /**
+     * Replaces sentences without preparing/reloading media, preserving playback
+     * position and state so a background boundary refresh can apply immediately.
+     */
+    fun updateSentences(mediaId: String, sentences: List<SentenceBoundary>): Boolean {
+        val index = mediaItems.indexOfFirst { it.id == mediaId }
+        if (index < 0) {
+            return false
+        }
+        val updatedItem = mediaItems[index].copy(sentences = sentences)
+        if (mediaItems[index] == updatedItem) {
+            return true
+        }
+        mediaItems[index] = updatedItem
+        if (index == player.currentMediaItemIndex) {
+            listeners.forEach { it.onMediaChanged(updatedItem) }
+            notifySentenceIfChanged(force = true)
+            notifySnapshot()
+        }
+        return true
+    }
+
     fun play() {
         player.play()
     }

android/oral-trainer-sdk/src/main/java/cn/learningpad/oraltrainer/sdk/SentenceBoundaryApi.kt

@@ -111,6 +111,7 @@ class SentenceBoundaryApi internal constructor(
                 connection.requestMethod = "GET"
                 connection.connectTimeout = config.connectTimeoutMs
                 connection.readTimeout = config.readTimeoutMs
+                connection.useCaches = false
                 connection.setRequestProperty("Accept", "application/json")
                 connection.setRequestProperty("User-Agent", config.userAgent)
                 val statusCode = connection.responseCode

android/sample-app/src/main/java/cn/learningpad/oraltrainer/sample/MainActivity.kt

@@ -107,6 +107,7 @@ class MainActivity : Activity() {
 
     private var activeItemId: String = ""
     private var currentSentenceCount = 0
+    private var sentenceBoundaryRequestGeneration = 0
     private var catalogVideos: List<TrainingVideoSummary> = emptyList()
     private var catalogStatusTextValue = "正在同步"
     private var activeModule = Module.TRAIN
@@ -1419,6 +1420,9 @@ class MainActivity : Activity() {
                     catalogStatusText.text = catalogStatusTextValue
                 }
                 renderCatalog()
+                catalogVideos
+                    .firstOrNull { it.videoHash == activeItemId }
+                    ?.let { refreshSentenceBoundaries(it, background = true) }
             }
 
             override fun onError(error: Throwable) {
@@ -1460,18 +1464,38 @@ class MainActivity : Activity() {
         val loadingItem = video.toTrainingMediaItem()
         controller.loadItem(loadingItem)
         currentSentenceCount = video.sentenceCount
+        refreshSentenceBoundaries(video, background = false)
+    }
+
+    private fun refreshSentenceBoundaries(
+        video: TrainingVideoSummary,
+        background: Boolean,
+    ) {
+        val requestGeneration = ++sentenceBoundaryRequestGeneration
+        if (!background && ::statusText.isInitialized) {
+            statusText.text = "正在加载云端课程..."
+        } else if (::statusText.isInitialized) {
+            statusText.text = "正在刷新句子边界..."
+        }
         sdk.sentenceBoundaryApi.fetch(video.videoHash, object : SentenceBoundaryApiCallback {
             override fun onSuccess(result: SentenceBoundaryApiResult) {
-                if (activeItemId != video.videoHash) {
+                if (
+                    sentenceBoundaryRequestGeneration != requestGeneration ||
+                    activeItemId != video.videoHash
+                ) {
                     return
                 }
                 currentSentenceCount = result.sentences.size
-                controller.loadItem(video.toTrainingMediaItem(result.sentences))
+                controller.updateSentences(video.videoHash, result.sentences)
+                refreshCurrentUi()
                 statusText.text = "课程已就绪：${result.sentences.size} 句"
             }
 
             override fun onError(error: Throwable) {
-                if (activeItemId != video.videoHash) {
+                if (
+                    sentenceBoundaryRequestGeneration != requestGeneration ||
+                    activeItemId != video.videoHash
+                ) {
                     return
                 }
                 statusText.text = "句子边界加载失败：${error.message.orEmpty()}"