开篇废话

最近学习了Kotlin，学习了Jetpack，发现是真香，所以就手写了一个MVVM的框架，可以方便开发。Kotlin+Jetpack+MVVM之GitHub地址，帮我点个Star，赠人玫瑰，手留余香，谢谢。

先讲一下思路

ViewModel

ViewModel可以放一些数据和网络请求，通过LiveData回调给V层数据，因为LiveData会传入Lifecycle，可以防止内存泄漏。

Activity & Fragment

V层可以通过ViewModelStore拿到相应作用域的ViewModel，通过ViewModel去获取数据。

其它

同时简单封装了几个网络请求之后V层比较关心的请求结果的成功失败以及列表是否还有更多数据。
还封装了一个LiveData的扩展函数，减少V层逻辑，使代码更清晰。

上核心代码

对ViewModel进行封装

package com.cc.mvvm.mvvm

import android.os.Bundle
import android.util.Log
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel

/**
 * Created by guoshichao on 2021/2/20
 * MVVM BaseModel
 */
abstract class BaseViewModel : ViewModel() {

    val loadStateLiveData = MutableLiveData<LoadState>()
    val hasMoreStateLiveData = MutableLiveData<HasMoreState>()

    open fun init(arguments: Bundle?) {}

    /**
     * 加载数据开始  用调用V层的loadStart
     */
    protected fun loadStart() {
        loadStateLiveData.value = LoadState.LoadStart
    }

    /**
     * 加载数据结束  用调用V层的loadFinish
     */
    protected fun loadFinish(success: Boolean) {
        if (success) {
            loadStateLiveData.setValue(LoadState.LoadSuccess)
        } else {
            loadStateLiveData.setValue(LoadState.LoadFail)
        }
    }

    /**
     * 是否有更多数据  用调用V层的HasMore和noMore
     */
    protected fun hasMore(hasMore : Boolean){
        if (hasMore) {
            hasMoreStateLiveData.value = HasMoreState.HasMore
        } else {
            hasMoreStateLiveData.value = HasMoreState.NoMore
        }
    }

    override fun onCleared() {
        Log.v("BaseViewModel", this.javaClass.name + this + " onCleared()")
        super.onCleared()
    }

}

对Activity进行封装

package com.cc.mvvm.mvvm

import android.os.Bundle
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.ViewModelStoreOwner
import androidx.viewbinding.ViewBinding
import com.cc.mvvm.base.BaseActivity
import java.lang.reflect.ParameterizedType

/**
 * Created by guoshichao on 2021/2/20
 * MVVM BaseActivity
 */
abstract class MVVMBaseActivity<V : ViewBinding, M : BaseViewModel> : BaseActivity() {

    protected lateinit var mViewBinding: V

    protected lateinit var mViewModel: M

    public override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        onPrepare()
        mViewBinding = getViewBinding()
        setContentView(mViewBinding.root)
        mViewModel = getViewModel()!!
        mViewModel.init(if (intent != null) intent.extras else null)
        loadState()
        onRegisterLiveListener()
        liveDataObserver()
        init()
    }

    /**
     * 预配置
     */
    protected open fun onPrepare() {}

    /**
     * 获取ViewBinding
     */
    abstract fun getViewBinding(): V

    /**
     * 返回ViewModelStoreOwner
     */
    protected open fun getViewModelStoreOwner() : ViewModelStoreOwner {
        return this
    }

    /**
     * 获取ViewModel
     */
    protected open fun getViewModel(): M? {
        //这里获得到的是类的泛型的类型
        val type = javaClass.genericSuperclass
        if (type != null && type is ParameterizedType) {
            val actualTypeArguments = type.actualTypeArguments
            val tClass = actualTypeArguments[1]
            return ViewModelProvider(getViewModelStoreOwner(),
                    ViewModelProvider.AndroidViewModelFactory.getInstance(application))
                    .get(tClass as Class<M>)
        }
        return null
    }

    /**
     * LiveEventBus的Listener
     */
    protected open fun onRegisterLiveListener() {}

    /**
     * LiveData的Observer
     */
    protected abstract fun liveDataObserver()

    /**
     * 回调刷新控件状态
     */
    private fun loadState() {
        mViewModel.loadStateLiveData.observe(this, Observer {
            when (it) {
                LoadState.LoadStart -> loadStart()
                LoadState.LoadSuccess -> loadFinish(true)
                LoadState.LoadFail -> loadFinish(false)
            }
        })
        mViewModel.hasMoreStateLiveData.observe(this, Observer {
            when (it) {
                HasMoreState.HasMore -> hasMore()
                HasMoreState.NoMore -> noMore()
            }
        })
    }

    /**
     * 初始化
     */
    protected abstract fun init()

    //加载开始
    protected open fun loadStart() {}

    //加载结束
    protected open fun loadFinish(success: Boolean) {}

    //有下一页
    protected open fun hasMore() {}

    //无下一页
    protected open fun noMore() {}

}

对Fragment进行封装

package com.cc.mvvm.mvvm

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.ViewModelStoreOwner
import androidx.viewbinding.ViewBinding
import com.cc.mvvm.base.BaseFragment
import java.lang.reflect.ParameterizedType

/**
 * Created by guoshichao on 2021/2/20
 * MVVM BaseFragment
 */
abstract class MVVMBaseFragment<V : ViewBinding, M : BaseViewModel> : BaseFragment() {

    protected lateinit var mViewBinding: V

    protected lateinit var mViewModel: M

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        onPrepare()
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        mViewBinding = getViewBinding()

        return mViewBinding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        load()
    }

    private fun load() {
        mViewModel = getViewModel()!!
        mViewModel.init(arguments)
        loadState()
        onRegisterLiveListener()
        liveDataObserver()
        init()
    }

    /**
     * 预配置
     */
    protected open fun onPrepare() {}

    /**
     * 获取ViewBinding
     */
    abstract fun getViewBinding(): V

    /**
     * 返回ViewModelStoreOwner
     */
    protected open fun getViewModelStoreOwner() : ViewModelStoreOwner {
        return this
    }

    /**
     * 获取ViewModel
     */
    protected open fun getViewModel(): M? {
        //这里获得到的是类的泛型的类型
        val type = javaClass.genericSuperclass
        if (type != null && type is ParameterizedType) {
            val actualTypeArguments = type.actualTypeArguments
            val tClass = actualTypeArguments[1]
            return ViewModelProvider(getViewModelStoreOwner(),
                    ViewModelProvider.AndroidViewModelFactory.getInstance(activity!!.application))
                    .get(tClass as Class<M>)
        }
        return null
    }

    /**
     * LiveEventBus的Listener
     */
    protected open fun onRegisterLiveListener() {}

    /**
     * LiveData的Observer
     */
    protected abstract fun liveDataObserver()

    /**
     * 初始化
     */
    protected abstract fun init()

    /**
     * 回调刷新控件状态
     */
    private fun loadState() {
        mViewModel.loadStateLiveData.observe(viewLifecycleOwner, Observer {
            when (it) {
                LoadState.LoadStart -> loadStart()
                LoadState.LoadSuccess -> loadFinish(true)
                LoadState.LoadFail -> loadFinish(false)
            }
        })
        mViewModel.hasMoreStateLiveData.observe(viewLifecycleOwner, Observer {
            when (it) {
                HasMoreState.HasMore -> hasMore()
                HasMoreState.NoMore -> noMore()
            }
        })
    }

    //加载开始
    protected open fun loadStart() {}

    //加载结束
    protected open fun loadFinish(success: Boolean) {}

    //有下一页
    protected open fun hasMore() {}

    //无下一页
    protected open fun noMore() {}

}

其它封装

LoadState的封装

package com.cc.mvvm.mvvm

enum class LoadState {
    LoadStart, LoadSuccess, LoadFail
}

HasMoreState的封装

package com.cc.mvvm.mvvm

enum class HasMoreState {
    HasMore, NoMore
}

LiveData扩展函数封装

package com.cc.mvvm.mvvm

import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer

fun <T> LifecycleOwner.observe(liveData: LiveData<T>, observer: (t: T) -> Unit) {
    liveData.observe(this, Observer { it?.let { t -> observer(t) } })
}

BaseActivity & BaseFragment

大家可以直接继承自己项目中的BaseActivity和BaseFragment，也可以使用我的，主要是加了一些Log，方便观察bug及数据等。
BaseActivity

package com.cc.mvvm.base;

import android.app.Activity;
import android.content.Intent;
import android.content.pm.ActivityInfo;
import android.content.res.TypedArray;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;

import androidx.appcompat.app.AppCompatActivity;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * Created by guoshichao on 2021/4/28
 */
public class BaseActivity extends AppCompatActivity {

    protected void onCreate(Bundle args) {
        if (Build.VERSION.SDK_INT == 26 && this.isTranslucentOrFloating()) {
            boolean result = this.fixOrientation();
            Log.i("BaseActivity", "onCreate fixOrientation when Oreo, result = " + result);
        }

        super.onCreate(args);
        Log.v("BaseActivity", this.getClass().getName() + " onCreate()");
    }

    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        Log.v("BaseActivity", this.getClass().getName() + " onSaveInstanceState()");
    }

    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        Log.v("BaseActivity", this.getClass().getName() + " onRestoreInstanceState()");
    }

    protected void onStart() {
        super.onStart();
        Log.v("BaseActivity", this.getClass().getName() + " onStart()");
    }

    protected void onResume() {
        super.onResume();
        Log.v("BaseActivity", this.getClass().getName() + " onResume()");
    }

    protected void onPause() {
        super.onPause();
        Log.v("BaseActivity", this.getClass().getName() + " onPause()");
    }

    protected void onStop() {
        super.onStop();
        Log.v("BaseActivity", this.getClass().getName() + " onStop()");
    }

    protected void onDestroy() {
        super.onDestroy();
        Log.v("BaseActivity", this.getClass().getName() + " onCreate()");
    }

    private boolean isTranslucentOrFloating() {
        boolean isTranslucentOrFloating = false;

        try {
            int[] styleableRes = (int[])((int[])Class.forName("com.android.internal.R$styleable").getField("Window").get((Object)null));
            TypedArray ta = this.obtainStyledAttributes(styleableRes);
            Method m = ActivityInfo.class.getMethod("isTranslucentOrFloating", TypedArray.class);
            m.setAccessible(true);
            isTranslucentOrFloating = (Boolean)m.invoke((Object)null, ta);
            m.setAccessible(false);
        } catch (Exception var5) {
            var5.printStackTrace();
        }

        return isTranslucentOrFloating;
    }

    private boolean fixOrientation() {
        try {
            Field field = Activity.class.getDeclaredField("mActivityInfo");
            field.setAccessible(true);
            ActivityInfo o = (ActivityInfo)field.get(this);
            o.screenOrientation = -1;
            field.setAccessible(false);
            return true;
        } catch (Exception var3) {
            var3.printStackTrace();
            return false;
        }
    }

    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        Log.v("BaseActivity", this.getClass().getName() + " onNewIntent()");
    }

}

BaseFragment

package com.cc.mvvm.base;

import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

/**
 * Created by guoshichao on 2021/4/28
 */
public class BaseFragment extends Fragment {

    public void onAttach(Activity activity) {
        super.onAttach(activity);
        Log.v("BaseFragment", this.getClass().getName() + this + " onAttach()");
    }

    @TargetApi(22)
    public void onAttach(Context context) {
        super.onAttach(context);
        Log.v("BaseFragment", this.getClass().getName() + this + " onAttach()");
    }

    public void onDetach() {
        Log.v("BaseFragment", this.getClass().getName() + this + " onDetach()");
        super.onDetach();
    }

    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.v("BaseFragment", this.getClass().getName() + this + " onCreate()");
    }

    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        Log.v("BaseFragment", this.getClass().getName() + this + " onCreateView()");
        View contentView = super.onCreateView(inflater, container, savedInstanceState);
        return contentView;
    }

    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        Log.v("BaseFragment", this.getClass().getName() + this + " setUserVisibleHint(), isVisibleToUser:" + isVisibleToUser);
    }

    public void onStart() {
        super.onStart();
        Log.v("BaseFragment", this.getClass().getName() + this + " onStart()");
    }

    public void onResume() {
        super.onResume();
        Log.v("BaseFragment", this.getClass().getName() + this + " onResume()");
    }

    public void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);
        Log.v("BaseFragment", this.getClass().getName() + this + " onSaveInstanceState()");
    }

    public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
        super.onViewStateRestored(savedInstanceState);
        Log.v("BaseFragment", this.getClass().getName() + this + " onViewStateRestored()");
    }

    public void onPause() {
        super.onPause();
        Log.v("BaseFragment", this.getClass().getName() + this + " onPause()");
    }

    public void onStop() {
        super.onStop();
        Log.v("BaseFragment", this.getClass().getName() + this + " onStop()");
    }

    public void onDestroyView() {
        super.onDestroyView();
        Log.v("BaseFragment", this.getClass().getName() + this + " onDestroyView()");
    }

    public void onDestroy() {
        super.onDestroy();
        Log.v("BaseFragment", this.getClass().getName() + this + " onDestroy()");
    }

}

使用Demo

V层

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/tv_hello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.kt

package com.cc.kotlin_jetpack_mvvm

import android.widget.Toast
import com.cc.kotlin_jetpack_mvvm.databinding.ActivityMainBinding
import com.cc.mvvm.mvvm.MVVMBaseActivity
import com.cc.mvvm.mvvm.observe

class MainActivity : MVVMBaseActivity<ActivityMainBinding, MainViewModel>() {

    override fun getViewBinding(): ActivityMainBinding {
        return ActivityMainBinding.inflate(layoutInflater)
    }

    override fun liveDataObserver() {
        observe(mViewModel.modelLiveData, ::showToast)
    }

    private fun showToast(message : String) {
        Toast.makeText(this, message, Toast.LENGTH_LONG).show()
    }

    override fun init() {
        mViewBinding.tvHello.setOnClickListener{
            mViewModel.getModel()
        }
    }

}

MainViewModel.kt

package com.cc.kotlin_jetpack_mvvm

import androidx.lifecycle.MutableLiveData
import com.cc.mvvm.mvvm.BaseViewModel

/**
 * Created by guoshichao on 2021/4/28
 */
class MainViewModel : BaseViewModel() {

    val modelLiveData = MutableLiveData<String>()

    fun getModel() {
        modelLiveData.value = "Hello!!!"
    }

}

结束小语

总来来说，封装的还是比较简单的，因为很多工作Jetpack已经帮我们去处理了，不需要我们过多的去做什么。

更多内容戳这里（整理好的各种文集）

Android Kotlin+Jetpack+MVVM