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app%2Fsrc%2Fmain%2Fjava%2Fcom%2Fexample%2Fmyapplication/NoteViewModel.kt

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+// 负责人：李琦 | 模块：ViewModel层 | 功能：便签业务逻辑管理
+// 创建时间：2026年5月7日
+
+package com.example.myapplication.viewmodel
+
+import android.app.Application
+import androidx.lifecycle.AndroidViewModel
+import androidx.lifecycle.viewModelScope
+import com.example.myapplication.data.Note
+import com.example.myapplication.data.NoteDatabase
+import com.example.myapplication.data.NoteRepository
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.launch
+
+/**
+ * 便签 ViewModel - 李琦负责
+ * 
+ * 负责管理便签相关的业务逻辑和 UI 状态
+ * 作为 View 层和 Model 层之间的桥梁
+ * 
+ * @param application 应用程序上下文
+ */
+class NoteViewModel(application: Application) : AndroidViewModel(application) {
+    
+    // 数据仓库实例
+    private val repository: NoteRepository
+    
+    // 所有便签列表的状态流
+    private val _allNotes = MutableStateFlow<List<Note>>(emptyList())
+    val allNotes: StateFlow<List<Note>> = _allNotes.asStateFlow()
+    
+    // 当前编辑的便签
+    private val _currentNote = MutableStateFlow<Note?>(null)
+    val currentNote: StateFlow<Note?> = _currentNote.asStateFlow()
+    
+    // 加载状态
+    private val _isLoading = MutableStateFlow(false)
+    val isLoading: StateFlow<Boolean> = _isLoading.asStateFlow()
+    
+    init {
+        // 初始化数据仓库
+        val noteDao = NoteDatabase.getDatabase(application).noteDao()
+        repository = NoteRepository(noteDao)
+        
+        // 开始监听数据库变化
+        observeNotes()
+    }
+    
+    /**
+     * 监听便签数据变化
+     * 
+     * 当数据库中的便签数据发生变化时，自动更新 StateFlow
+     */
+    private fun observeNotes() {
+        viewModelScope.launch {
+            repository.getAllNotes().collect { notes ->
+                _allNotes.value = notes
+            }
+        }
+    }
+    
+    /**
+     * 加载指定 ID 的便签
+     * 
+     * @param noteId 便签 ID
+     */
+    fun loadNote(noteId: Int) {
+        viewModelScope.launch {
+            repository.getNoteById(noteId).collect { note ->
+                _currentNote.value = note
+            }
+        }
+    }
+    
+    /**
+     * 创建新便签
+     * 
+     * @param title 便签标题
+     * @param content 便签内容
+     */
+    fun createNote(title: String, content: String) {
+        viewModelScope.launch {
+            val note = Note(
+                title = title,
+                content = content,
+                createTime = System.currentTimeMillis(),
+                updateTime = System.currentTimeMillis()
+            )
+            repository.createNote(note)
+        }
+    }
+    
+    /**
+     * 更新现有便签
+     * 
+     * @param note 要更新的便签对象
+     */
+    fun updateNote(note: Note) {
+        viewModelScope.launch {
+            val updatedNote = note.copy(updateTime = System.currentTimeMillis())
+            repository.updateNote(updatedNote)
+        }
+    }
+    
+    /**
+     * 保存便签（创建或更新）
+     * 
+     * @param title 便签标题
+     * @param content 便签内容
+     * @param noteId 如果是编辑现有便签，传入其 ID；否则传 0 或 null
+     */
+    fun saveNote(title: String, content: String, noteId: Int? = null) {
+        viewModelScope.launch {
+            _isLoading.value = true
+            try {
+                if (noteId != null && noteId > 0) {
+                    // 更新现有便签
+                    val existingNote = _currentNote.value
+                    if (existingNote != null) {
+                        updateNote(existingNote.copy(title = title, content = content))
+                    }
+                } else {
+                    // 创建新便签
+                    createNote(title, content)
+                }
+            } finally {
+                _isLoading.value = false
+            }
+        }
+    }
+    
+    /**
+     * 删除便签
+     * 
+     * @param note 要删除的便签对象
+     */
+    fun deleteNote(note: Note) {
+        viewModelScope.launch {
+            repository.deleteNote(note)
+        }
+    }
+    
+    /**
+     * 根据 ID 删除便签
+     * 
+     * @param noteId 要删除的便签 ID
+     */
+    fun deleteNoteById(noteId: Int) {
+        viewModelScope.launch {
+            repository.deleteNoteById(noteId)
+        }
+    }
+    
+    /**
+     * 清空当前编辑的便签
+     */
+    fun clearCurrentNote() {
+        _currentNote.value = null
+    }
+}