一、MVVM是什么？

MVVM分为Model，View，ViewModel 三个部分

Model:数据层，包含数据实体和对数据实体的操作

View:UI层，对应于Activity，XML，负责数据显示以及用户交互。

ViewModel：中间层，作为中间桥梁 去通知model数据层处理数据业务，并将结果通知给 UI 层处理 UI 逻辑。ViewModel中只有Activity持有ViewModel引用，ViewModel是不持有Activity的引用的。ViewModel生命周期大于Activity，如果持有Activity的引用，容易引起内存泄漏。ViewModel结合Jetpack的LiveData通过观察者回调的方式，在数据更新时通知UI层。

二、使用步骤：

1.配置gradle

implementation 'androidx.lifecycle:lifecycle-viewmodel:2.3.0'

2.继承ViewModel类

class RecordMapViewModel : ViewModel()

3.Activity中调用ViewModel获取数据

val viewModel=ViewModelProvider(this).get(RecordMapViewModel::class.java)

三、代码实例：

  RecordMapViewModel

class RecordMapViewModel : ViewModel() {private val mMLDLDSweepMap: MutableLiveData by lazy {MutableLiveData()}private val mIRecordMapModel: IRecordMapModel by lazy {RecordMapModel()}fun getMLDLDSweepMap() = mMLDLDSweepMapfun getMapData(bucket: String, path: String) {mIRecordMapModel.getMapData(bucket, path, object : ICallback {override fun callback(data: Any?) {ProgressUtil.hideLoading()if (data is LDSweepMap) {mMLDLDSweepMap.postValue(data)}}})}
}

RecordMapViewModel

class RecordMapModel : IRecordMapModel {companion object {@JvmStaticprivate val TAG = "RecordMapModel"}override fun getMapData(bucket: String, path: String, callback: ICallback) {LDSweeper.getInstance().tuyaSweeper?.getSweeperByteData(bucket, path, object : ITuyaByteDataListener {override fun onSweeperByteData(data: ByteArray?) {LogUtil.i(TAG, "getSweeperByteData success")callback.callback(DataUtil.byteToLDSweepMap(data))}override fun onFailure(code: Int, msg: String?) {LogUtil.i(TAG, "getSweeperByteData onFailure:  $msg")callback.callback(null)}});}
}

IRecordMapModel

interface IRecordMapModel {fun getMapData(bucket: String, path: String, callback: ICallback)
}

RecordMapActivity

public class RecordMapActivity extends BaseActivity {private final String TAG = "RecordMapActivity";RecordMapViewModel mRecordMapViewModel;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);mRecordMapViewModel = new ViewModelProvider(this).get(RecordMapViewModel.class);initData();}private void initData() {MutableLiveData mapMutableLiveData = mRecordMapViewModel.getMLDLDSweepMap();mapMutableLiveData.observe(this, new Observer() {@Overridepublic void onChanged(LDSweepMap ldMap) {}});mRecordMapViewModel.getMapData(bucket, file);}}