255 lines
3.8 KiB
Markdown
255 lines
3.8 KiB
Markdown
# Jetpack组件
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## 目录
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- [Lifecycle](#lifecycle)
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- [ViewModel](#viewmodel)
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- [LiveData](#livedata)
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- [Room](#room)
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- [Navigation](#navigation)
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- [WorkManager](#workmanager)
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- [Paging](#paging)
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- [DataBinding](#databinding)
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- [Jetpack最佳实践](#jetpack最佳实践)
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- [面试常见问题](#面试常见问题)
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---
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## Lifecycle
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### Lifecycle 简介
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```java
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// Lifecycle：生命周期感知组件
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// 自动管理生命周期相关的操作
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```
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### 使用方式
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```java
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// 实现 LifecycleObserver
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public class MyObserver implements LifecycleObserver {
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@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
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public void onResume() {
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// Activity onResume 时调用
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}
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}
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// 注册观察者
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lifecycle.addObserver(new MyObserver());
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```
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---
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## ViewModel
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### ViewModel 简介
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```java
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// ViewModel：保存 UI 相关数据
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// 在配置变更时保持数据
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```
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### 使用方式
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```java
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public class MyViewModel extends ViewModel {
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private MutableLiveData<String> data = new MutableLiveData<>();
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public LiveData<String> getData() {
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return data;
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}
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public void setData(String value) {
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data.setValue(value);
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}
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}
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// Activity 中使用
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MyViewModel viewModel = ViewModelProviders.of(this).get(MyViewModel.class);
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viewModel.getData().observe(this, data -> {
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// 更新 UI
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});
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```
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---
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## LiveData
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### LiveData 简介
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```java
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// LiveData：可观察的数据持有者
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// 自动更新 UI
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// 生命周期感知
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```
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### 使用方式
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```java
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MutableLiveData<String> liveData = new MutableLiveData<>();
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liveData.observe(this, new Observer<String>() {
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@Override
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public void onChanged(String s) {
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// 数据变化时自动更新
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}
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});
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liveData.setValue("New Value");
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```
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---
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## Room
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### Room 简介
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```java
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// Room：SQLite 数据库抽象层
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// 编译时检查
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// 支持 LiveData、RxJava
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```
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### 使用方式
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```java
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@Database(entities = {User.class}, version = 1)
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public abstract class AppDatabase extends RoomDatabase {
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public abstract UserDao userDao();
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}
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@Dao
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public interface UserDao {
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@Query("SELECT * FROM user")
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LiveData<List<User>> getAllUsers();
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}
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```
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---
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## Navigation
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### Navigation 简介
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```java
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// Navigation：导航组件
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// 简化 Fragment 导航
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```
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### 使用方式
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```java
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// 导航到目标
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Navigation.findNavController(view)
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.navigate(R.id.action_fragmentA_to_fragmentB);
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```
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---
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## WorkManager
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### WorkManager 简介
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```java
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// WorkManager：后台任务管理
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// 保证任务执行
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// 支持约束条件
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```
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### 使用方式
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```java
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WorkRequest workRequest = new OneTimeWorkRequest.Builder(MyWorker.class)
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.setConstraints(new Constraints.Builder()
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.setRequiredNetworkType(NetworkType.CONNECTED)
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.build())
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.build();
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WorkManager.getInstance(context).enqueue(workRequest);
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```
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---
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## Paging
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### Paging 简介
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```java
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// Paging：分页加载数据
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// 自动处理分页逻辑
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```
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---
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## DataBinding
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### DataBinding 简介
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```java
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// DataBinding：数据绑定
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// 减少 findViewById
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// 自动更新 UI
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```
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### 使用方式
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```xml
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<layout>
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<data>
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<variable name="user" type="User" />
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</data>
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<TextView
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android:text="@{user.name}" />
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</layout>
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```
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---
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## Jetpack最佳实践
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### 1. 使用 ViewModel 保存数据
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```java
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// 配置变更时保持数据
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```
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### 2. 使用 LiveData 更新 UI
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```java
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// 自动更新，生命周期感知
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```
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### 3. 使用 Room 管理数据
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```java
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// 类型安全，编译时检查
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```
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---
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## 面试常见问题
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### Q1: ViewModel 的作用？
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**答案：**
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- 保存 UI 相关数据
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- 在配置变更时保持数据
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- 与 Activity/Fragment 生命周期分离
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### Q2: LiveData 的特点？
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**答案：**
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- 可观察
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- 生命周期感知
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- 自动更新 UI
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### Q3: Room 的优势？
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**答案：**
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- 编译时检查
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- 类型安全
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- 支持 LiveData、RxJava
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---
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*最后更新：2024年*
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