关于MVVM的介绍,我们可以参考之前的文章:
Android App开发架构之:MVVM
和MVP相比,MVVM有相似的地方,也有各自的特点。
相似点:
区别:
4. MVVM使用LiveData,LiveData是一个具有生命周期感知功能的数据持有者类;也就是使用LiveData时,可以不用关心activity和fragment的生命周期可能带来的内存泄漏问题,因为LiveData会在activity和fragment生命周期结束时立即取消订阅。
5. MVP为了解决内存泄漏,需要手动实现,比如采用弱引用,或者RxJava的Disposable、RxLifecycle或者AutoDispose方案。参考:TinyMVP:一种全方案解决内存泄漏的MVP架构
同TinyMVP,TinyMVVM的ViewModel和Repository也是通过泛型来自动生成实例:
public class Type1Activity extends BaseMVVMActivity<Type1ViewModel> {
......
}
public class Type1ViewModel extends BaseViewModel<Type1Repository> {
......
}
接下来会有三种形式的使用方式:
ViewModel只负责业务接口;
Repository负责LiveData变量生成以及数据处理;
通过代码可以看到,这里的Type1ViewModel提供V层调用的接口loadData1和loadData2;
并且通过getLiveData1和getLiveData2提供给V层livedata变量;
public class Type1ViewModel extends BaseViewModel<Type1Repository> {
public Type1ViewModel(@NonNull Application application) {
super(application);
}
public LiveData<Boolean> getLiveData1() {
return repository.getLiveData1();
}
public LiveData<String> getLiveData2() {
return repository.getLiveData2();
}
public void loadData1() {
repository.getData1();
}
public void loadData2() {
repository.getData2();
}
}
Type1Repository负责提供livedata变量比如mLiveData1、mLiveData2,已经具体获取数据的方法如getData1、getData2;
public class Type1Repository extends BaseRepository {
protected MutableLiveData<Boolean> mLiveData1;
protected MutableLiveData<String> mLiveData2;
public LiveData<Boolean> getLiveData1() {
if (mLiveData1 == null) {
mLiveData1 = new MutableLiveData<>();
}
return mLiveData1;
}
public LiveData<String> getLiveData2() {
if (mLiveData2 == null) {
mLiveData2 = new MutableLiveData<>();
}
return mLiveData2;
}
public void getData1() {
Observable.create((ObservableOnSubscribe<Boolean>) emitter -> {
try {
Thread.sleep(2000); // 假设此处是耗时操作
} catch (Exception e) {
e.printStackTrace();
emitter.onError(new RuntimeException());
}
emitter.onNext(true);
}
)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<Boolean>() {
@Override
public void onSubscribe(Disposable d) {
}
@Override
public void onNext(Boolean orderValues) {
mLiveData1.setValue(orderValues);
}
@Override
public void onError(Throwable e) {
}
@Override
public void onComplete() {
}
});
}
public void getData2() {
......
}
}
ViewModel负责业务变量接口以及LiveData变量;
Repository负责获取数据,Repository和ViewModel之间如果涉及到异步调用问题,Repository的方法采用RxJava的Observable的返回值类型,返回给ViewModel调用方处理。
通过代码可以看到,Type2ViewModel生成了mLiveData1和mLiveData2变量,这些变量可以通过getLiveData1和getLiveData2供V层调用,并且提供了getLiveData1和getLiveData1方法。
public class Type2ViewModel extends BaseViewModel<Type2Repository> {
protected MutableLiveData<Boolean> mLiveData1;
protected MutableLiveData<String> mLiveData2;
public Type2ViewModel(@NonNull Application application) {
super(application);
}
public LiveData<Boolean> getLiveData1() {
if (mLiveData1 == null) {
mLiveData1 = new MutableLiveData<>();
}
return mLiveData1;
}
public LiveData<String> getLiveData2() {
if (mLiveData2 == null) {
mLiveData2 = new MutableLiveData<>();
}
return mLiveData2;
}
public void loadData1() {
repository.getData1().subscribe(new Observer<Boolean>() {
@Override
public void onSubscribe(Disposable d) {
}
@Override
public void onNext(Boolean orderValues) {
mLiveData1.setValue(orderValues);
}
@Override
public void onError(Throwable e) {
}
@Override
public void onComplete() {
}
});
}
public void loadData2() {
......
}
}
而Type2Repository的getData1和getData2由于异步处理数据,返回了Observable类型。
public class Type2Repository extends BaseRepository {
public Observable<Boolean> getData1() {
return Observable.create((ObservableOnSubscribe<Boolean>) emitter -> {
try {
Thread.sleep(2000); // 假设此处是耗时操作
} catch (Exception e) {
e.printStackTrace();
emitter.onError(new RuntimeException());
}
emitter.onNext(true);
}
)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
public Observable<String> getData2() {
......
}
}
方案1和方案2都涉及到了LiveData类型的创建和使用,要么在ViewModel中创建,要么在Repository中创建。如果在Repository中创建,那么还得通过ViewModel让V层得到。
那么我们是否可以考虑将LiveData的创建和使用都统一管理起来呢,就像异步分发的EventBus这样。通过类似于EventBus这样的异步分发管理机制,我们可以在任意地方创建LiveData,并且可以在想要用到的地方获取到LiveData。
我们考虑使用单例和一个HashMap来实现,提供register和post功能:
public class TinyLiveBus {
private ConcurrentHashMap<String, MutableLiveData<Object>> liveDatas = new ConcurrentHashMap<>();
private static volatile TinyLiveBus sTinyBus;
public static TinyLiveBus getInstance() {
if (sTinyBus == null) {
return sTinyBus = new TinyLiveBus();
}
return sTinyBus;
}
public <T> MutableLiveData<T> register(String key, Class<T> clazz) {
if (!liveDatas.containsKey(key)) {
liveDatas.put(key, new MutableLiveData<>());
}
return (MutableLiveData<T>) liveDatas.get(key);
}
public <T> void post(String key, T value) {
if (liveDatas.containsKey(key)) {
MutableLiveData liveData = liveDatas.get(key);
liveData.postValue(value);
}
}
}
注:这里postValue表示在子线程和主线程里都可以使用,而setValue只能在主线程中使用。
在Activity中,我们通过TinyLiveBus.getInstance().register方法创建LiveData:
public class Type3Activity extends BaseMVVMActivity<Type3ViewModel> {
@Override
protected int getContentView() {
return R.layout.activity_type;
}
@Override
protected void init() {
Button btn = findViewById(R.id.button);
TinyLiveBus.getInstance()
.register("one", Boolean.class)
.observe(this, (Observer<Boolean>) bool -> btn.setText(bool ? "success" : "fail"));
Button btn2 = findViewById(R.id.button2);
TinyLiveBus.getInstance()
.register("two", String.class)
.observe(this, (Observer<String>) string -> btn2.setText(string));
}
public void clickMe(View view) {
mViewModel.loadData1();
}
public void clickOther(View view) {
mViewModel.loadData2();
}
}
在Repository中,我们通过TinyLiveBus.getInstance().post()通过LiveData有更新:
public class Type3Repository extends BaseRepository {
public void getData1() {
Observable.create((ObservableOnSubscribe<Boolean>) emitter -> {
try {
Thread.sleep(2000); // 假设此处是耗时操作
} catch (Exception e) {
e.printStackTrace();
emitter.onError(new RuntimeException());
}
emitter.onNext(true);
}
)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<Boolean>() {
@Override
public void onSubscribe(Disposable d) {
}
@Override
public void onNext(Boolean orderValues) {
TinyLiveBus.getInstance().post("one", orderValues);
}
@Override
public void onError(Throwable e) {
}
@Override
public void onComplete() {
}
});
}
public void getData2() {
......
}
}
https://github.com/ddnosh/android-tiny-mvvm
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