adding ability to lazily create viewmodels

- helpful when multiple view models are injected but not all are needed

vector/src/main/java/im/vector/app/core/extensions/MavericksViewModel.kt

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2021 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package im.vector.app.core.extensions
+
+import androidx.activity.ComponentActivity
+import com.airbnb.mvrx.ActivityViewModelContext
+import com.airbnb.mvrx.Mavericks
+import com.airbnb.mvrx.MavericksState
+import com.airbnb.mvrx.MavericksViewModel
+import com.airbnb.mvrx.MavericksViewModelProvider
+
+inline fun <reified VM : MavericksViewModel<S>, reified S : MavericksState> ComponentActivity.lazyViewModel(): Lazy<VM> {
+    return lazy(mode = LazyThreadSafetyMode.NONE) {
+        MavericksViewModelProvider.get(
+                viewModelClass = VM::class.java,
+                stateClass = S::class.java,
+                viewModelContext = ActivityViewModelContext(this, intent.extras?.get(Mavericks.KEY_ARG)),
+                key = VM::class.java.name
+        )
+    }
+}