diff --git a/app/build.gradle b/app/build.gradle
index d3827dd..07590c3 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -21,6 +21,15 @@ android {
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
         }
     }
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_1_8.toString()
+    }
 }
 
 dependencies {
@@ -30,6 +39,9 @@ dependencies {
     implementation 'androidx.appcompat:appcompat:1.1.0'
     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
     implementation "androidx.recyclerview:recyclerview:1.1.0"
+    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0"
+    implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.2.0"
+
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'androidx.test.ext:junit:1.1.1'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/MainActivity.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/MainActivity.kt
index 42fe1e7..8c4f46f 100644
--- a/app/src/main/java/tw/andyang/kotlinandroidworkshop/MainActivity.kt
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/MainActivity.kt
@@ -2,14 +2,13 @@ package tw.andyang.kotlinandroidworkshop
 
 import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity
+import androidx.lifecycle.*
 import androidx.recyclerview.widget.DividerItemDecoration
 import androidx.recyclerview.widget.LinearLayoutManager
 import kotlinx.android.synthetic.main.activity_main.*
 
 class MainActivity : AppCompatActivity() {
 
-    private var todos = listOf<Todo>()
-
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
@@ -19,17 +18,14 @@ class MainActivity : AppCompatActivity() {
         recyclerView.layoutManager = LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false)
         recyclerView.addItemDecoration(DividerItemDecoration(this, LinearLayoutManager.VERTICAL))
 
-        todos = todos.toMutableList().apply {
-            add(Todo.Title(getString(R.string.todo_list_title)))
-        }
+        val todoViewModel = ViewModelProvider(this).get<TodoViewModel>()
 
-        adapter.submitList(todos)
+        todoViewModel.todoLiveData.observe(this, Observer { todos: List<Todo> ->
+            adapter.submitList(todos)
+        })
 
         buttonAdd.setOnClickListener {
-            todos = todos.toMutableList().apply {
-                add(Todo.Item("world", false))
-            }
-            adapter.submitList(todos)
+            todoViewModel.onNewTodo.postValue(Unit)
         }
     }
 }
\ No newline at end of file
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/TodoViewModel.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/TodoViewModel.kt
new file mode 100644
index 0000000..fdfab8b
--- /dev/null
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/TodoViewModel.kt
@@ -0,0 +1,22 @@
+package tw.andyang.kotlinandroidworkshop
+
+import androidx.lifecycle.LiveData
+import androidx.lifecycle.MediatorLiveData
+import androidx.lifecycle.MutableLiveData
+import androidx.lifecycle.ViewModel
+
+class TodoViewModel : ViewModel() {
+
+    val onNewTodo = MutableLiveData<Unit>()
+
+    val todoLiveData: LiveData<List<Todo>> = MediatorLiveData<List<Todo>>().apply {
+        addSource(onNewTodo) {
+            val todo = Todo.Item("note $count", false)
+            this.value = this.value!! + listOf(todo)
+            count++
+        }
+        value = mutableListOf(Todo.Title("This is a title"))
+    }
+
+    private var count = 0
+}
\ No newline at end of file