Adnroid Lifecycle管理组件生命周期 && LiveData && ViewModel

Lifecycle 组件指的是 android.arch.lifecycle 包下提供的各种类与接口，可以让开发者构建能感知其他组件（主要指Activity 、Fragment）生命周期（lifecycle-aware）的类。

其中 Lifecycle 使用两个主要的枚举类来表示其所关联组件的生命周期：

• Event 事件 从组件或者Lifecycle类分发出来的生命周期，它们和Activity／Fragment生命周期的事件一一对应。(ON_CREATE, ON_START, ON_RESUME, ON_PAUSE, ON_STOP, ON_DESTROY)；
• State 状态 当前组件的生命周期状态(INITIALIZED, DESTROYED, CREATED, STARTED, RESUMED)。

添加依赖配置：

 def lifecycle_version = "1.1.1"
    // ViewModel and LiveData
    implementation "android.arch.lifecycle:extensions:$lifecycle_version"
    // alternatively - just ViewModel
    implementation "android.arch.lifecycle:viewmodel:$lifecycle_version" // use -ktx for Kotlin
    // alternatively - just LiveData
    implementation "android.arch.lifecycle:livedata:$lifecycle_version"
    // alternatively - Lifecycles only (no ViewModel or LiveData).
    // Support library depends on this lightweight import
    implementation "android.arch.lifecycle:runtime:$lifecycle_version"

    annotationProcessor "android.arch.lifecycle:compiler:$lifecycle_version"
    // alternately - if using Java8, use the following instead of compiler
    implementation "android.arch.lifecycle:common-java8:$lifecycle_version"

    // optional - ReactiveStreams support for LiveData
    implementation "android.arch.lifecycle:reactivestreams:$lifecycle_version"

---

使用：

package com.loaderman.architecturecomponents;

import androidx.annotation.NonNull;
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.OnLifecycleEvent;

public interface IPresenter extends LifecycleObserver {

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    void onCreate(@NonNull LifecycleOwner owner);

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    void onResume(@NonNull LifecycleOwner owner);

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    void onPause(@NonNull LifecycleOwner owner);

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    void onStop(@NonNull LifecycleOwner owner);

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    void onDestroy(@NonNull LifecycleOwner owner);
}

package com.loaderman.architecturecomponents;

import android.util.Log;

public class Model {
    private static final String TAG = "Model";
    public static void startWork() {
        Log.d(TAG,"startWork");
    }

    public static void endWork() {
        Log.d(TAG,"endWork");
    }
}

package com.loaderman.architecturecomponents;

import android.content.Context;
import android.util.Log;

import androidx.annotation.NonNull;
import androidx.lifecycle.LifecycleOwner;

public class Presenter implements IPresenter {

    private static final String TAG = "Presenter";

    private Model model = new Model();
    private Context context;

    public Presenter(Context context) {
        this.context = context;
    }

    public void doWork(){
        model.startWork();
    }


    /**
     * 绑定远程服务
     */
    private void bindService(){
        Log.d(TAG,"bindService");
    }

    /**
     * 解绑远程服务
     */
    private void unbindService(){
        Log.d(TAG,"unbindService");
    }


    /**
     * 比如注册动态广播等操作可以转移到Presenter中，进一步降低Activity的复杂性
     */
    private void register(){
//        context.registerReceiver(null,null);
    }

    private void unregister(){
//        context.unregisterReceiver(null);
    }



    /**
     * 创建资源等
     * @param owner
     */
    @Override
    public void onCreate(@NonNull LifecycleOwner owner) {
        Log.e(TAG,"onCreate");
        register();
        bindService();
    }

    @Override
    public void onResume(@NonNull LifecycleOwner owner) {

    }

    @Override
    public void onPause(@NonNull LifecycleOwner owner) {

    }

    @Override
    public void onStop(@NonNull LifecycleOwner owner) {

    }

    /**
     * 释放资源等
     * @param owner
     */
    @Override
    public void onDestroy(@NonNull LifecycleOwner owner) {
        Log.e(TAG,"onDestroy");
        model.endWork();
        unregister();
        unbindService();
    }
}

package com.loaderman.architecturecomponents;

import androidx.appcompat.app.AppCompatActivity;


import android.os.Bundle;

public class MainActivity extends AppCompatActivity  {
    private static String TAG = MainActivity.class.getSimpleName();
    private Presenter presenter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        presenter = new Presenter(this);
        //为Lifecycle注册生命周期监听器
        getLifecycle().addObserver(presenter);
        presenter.doWork();
    }
}

LiveData 是一种持有可被观察数据的类（an observable data holder class）。和其他可被观察的类不同的是，LiveData是有生命周期感知能力的（lifecycle-aware,），这意味着它可以在 activities, fragments, 或者 services 生命周期是活跃状态时更新这些组件。

ViewModel 与 LiveData 之间的关系图如下：

使用：

package com.loaderman.architecturecomponents;

public interface BaseViewModel<T> {
    T loadData();
    void clearData();
}

package com.loaderman.architecturecomponents;

import android.util.Log;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;


public class UserViewModel extends ViewModel
        implements BaseViewModel<User> {

    private String TAG = UserViewModel.class.getSimpleName();

    private MutableLiveData<User> liveUser;

    public MutableLiveData<User> getData(){
        if(liveUser == null){
            liveUser = new MutableLiveData<User>();
        }

        liveUser.setValue(loadData());
        return this.liveUser;
    }

    public void changeData(){
        if(liveUser != null){
            liveUser.setValue(loadData());
        }
    }

    @Override
    public User loadData() {
        User user = new User();
        user.userId = "00"+(int) ((Math.random() * 10));
        user.name = "张三"+(int) ((Math.random() * 10));
        user.phone = "12531202310";
        Log.i(TAG, "loadData(): " + user.toString());
        return user;
    }

    @Override
    public void clearData() {

    }
}

package com.loaderman.architecturecomponents;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;


import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity  {
    private static String TAG = MainActivity.class.getSimpleName();
    private Button btn;
    private TextView tv;
    UserViewModel mUserViewModel;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv = findViewById(R.id.tv);
        btn = findViewById(R.id.btn);
        //  view model.observe
        mUserViewModel = ViewModelProviders.of(this).get(UserViewModel.class);
        mUserViewModel.getData().observe(this, new Observer<User>() {
            @Override
            public void onChanged(@Nullable User user) {
                if(user != null){
                    tv.setText(user.toString());
                }
            }
        });


        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(mUserViewModel != null && mUserViewModel.getData() != null){
                    mUserViewModel.changeData();
                }
            }
        });
    }
}

效果：