在 Agentic Workflows 期间，AgentRunner 类和 AgentSession 接口会发出响应式事件流，这些事件流表示模型的推理过程、工具调用和文本回答。本页面演示了如何使用 Kotlin 协程和 Jetpack Compose 收集事件并将其连接到界面。
了解 AgentEvent 接口
AgentSession.runAsync() 和 AgentRunner.runSingleTurnAsync() 方法会返回 Flow<AgentEvent> 流。您的应用无需等待整个推理循环完成，即可在智能体执行过程中接收实时更新：
事件类型 |
说明 |
典型界面操作 |
|
发出增量文本块 ( |
当 |
|
当 Gemini Nano 选择工具并准备执行该工具时发出（提供 |
显示正在处理指示器（例如，“正在检查订单状态…”）。 |
|
在应用完成执行工具函数时触发（提供 |
将工具状态转换为“已完成”。 |
在 ViewModel 类中收集事件
使用 Android ViewModel 类来协调提示分派，并将界面状态公开给 Compose 屏幕：
package com.example.ai.agent.ui
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import com.google.mlkit.genai.agent.AgentEvent
import com.google.mlkit.genai.agent.AgentRunner
import com.google.mlkit.genai.agent.AgentSession
import com.google.mlkit.genai.common.GenAiException
import com.google.mlkit.genai.prompt.Content
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.flow.catch
import kotlinx.coroutines.flow.update
import kotlinx.coroutines.launch
data class AgentUiState(
val messages: List<String> = emptyList(),
val currentResponse: String = "",
val activeToolStatus: String? = null,
val isLoading: Boolean = false,
val errorMessage: String? = null
)
class ChatViewModel(
private val runner: AgentRunner,
private val sessionId: String = "default_chat_session"
) : ViewModel() {
private val session: AgentSession = runner.getOrCreateSession(sessionId)
private val _uiState = MutableStateFlow(AgentUiState())
val uiState: StateFlow<AgentUiState> = _uiState.asStateFlow()
fun sendMessage(userText: String) {
_uiState.update {
it.copy(
messages = it.messages + userText,
currentResponse = "",
activeToolStatus = null,
isLoading = true,
errorMessage = null
)
}
viewModelScope.launch {
val content = Content.builder().text(userText).build()
session.runAsync(content)
.catch { e ->
val message = when {
e is GenAiException && e.errorCode == GenAiException.ErrorCode.MAX_TURNS_EXCEEDED ->
"Agent exceeded the maximum reasoning turns allowed."
e is GenAiException && e.errorCode == GenAiException.ErrorCode.NOT_AVAILABLE ->
"On-device AI is currently unavailable."
e is GenAiException && e.errorCode == GenAiException.ErrorCode.BUSY ->
"On-device AI is busy. Please try again."
else -> e.localizedMessage ?: "Agent error"
}
_uiState.update {
it.copy(
isLoading = false,
activeToolStatus = null,
errorMessage = message
)
}
}
.collect { event ->
when (event) {
is AgentEvent.TextMessage -> {
_uiState.update {
it.copy(
currentResponse = if (event.isPartial) {
it.currentResponse + event.text
} else {
event.text.ifEmpty { it.currentResponse }
},
activeToolStatus = null
)
}
}
is AgentEvent.FunctionCall -> {
_uiState.update {
it.copy(
activeToolStatus =
"Executing ${event.name}..."
)
}
}
is AgentEvent.FunctionResponse -> {
_uiState.update {
it.copy(
activeToolStatus =
"Received data from ${event.name}"
)
}
}
else -> {}
}
}
// Finalize message once stream completes
_uiState.update {
it.copy(
messages = it.messages + it.currentResponse,
currentResponse = "",
activeToolStatus = null,
isLoading = false
)
}
}
}
override fun onCleared() {
super.onCleared()
// Release session memory and cancel active coroutines
session.close()
}
}
直接提取文本 token
对于无需在界面中单独显示工具执行详情的对话式界面，请使用 Flow<AgentEvent> 接口上的 textTokens() 扩展函数：
import com.google.mlkit.genai.agent.textTokens
import com.google.mlkit.genai.prompt.Content
val content = Content.builder().text(userText).build()
session.runAsync(content)
.textTokens()
.collect { token ->
appendTokenToChatBubble(token)
}
在 Jetpack Compose 中渲染
在可组合函数中使用 AgentUiState 状态，以呈现流式传输的文本和实时工具活动：
package com.example.ai.agent.ui
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.material3.*
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
@Composable
fun AgentChatScreen(
viewModel: ChatViewModel,
modifier: Modifier = Modifier
) {
val state by viewModel.uiState.collectAsState()
var inputText by remember { mutableStateOf("") }
Column(modifier = modifier.fillMaxSize().padding(16.dp)) {
LazyColumn(
modifier = Modifier.weight(1f).fillMaxWidth(),
verticalArrangement = Arrangement.spacedBy(8.dp)
) {
items(state.messages) { message ->
Card(modifier = Modifier.fillMaxWidth()) {
Text(text = message, modifier = Modifier.padding(12.dp))
}
}
if (state.activeToolStatus != null) {
item {
Text(
text = state.activeToolStatus ?: "",
style = MaterialTheme.typography.bodySmall,
color = MaterialTheme.colorScheme.secondary
)
}
}
if (state.currentResponse.isNotEmpty()) {
item {
Card(
colors = CardDefaults.cardColors(
containerColor =
MaterialTheme.colorScheme.surfaceVariant
),
modifier = Modifier.fillMaxWidth()
) {
Text(
text = state.currentResponse,
modifier = Modifier.padding(12.dp)
)
}
}
}
}
Row(
modifier = Modifier.fillMaxWidth().padding(top = 8.dp),
horizontalArrangement = Arrangement.spacedBy(8.dp)
) {
TextField(
value = inputText,
onValueChange = { inputText = it },
modifier = Modifier.weight(1f),
placeholder = { Text("Ask about an order...") }
)
Button(
onClick = {
if (inputText.isNotBlank()) {
viewModel.sendMessage(inputText)
inputText = ""
}
},
enabled = !state.isLoading
) {
Text("Send")
}
}
}
}