Cannot generate view-model

Sometimes you may not have enough information to generate the view-model. For example, some information may still be loading, or the state is inconsistent for some reason.

In that case, your factory can return null instead of the vm, and the connector can return an alternative "placeholder widget".

To do that you'll need to declare the view-model as nullable ViewModel? in these 3 places:

• The StoreConnector
• The builder
• The fromStore method.

Then, check for null in the builder:

builder: (BuildContext context, ViewModel? vm) { 
  return (vm == null)
    ? Text("User not logged in")
    : MyHomePage(user: vm.user)

This is the complete code:

return StoreConnector<AppState, ViewModel?>( // 1. Nullable here

  vm: () => Factory(this),       
  builder: (BuildContext context, ViewModel? vm) { // 2. Nullable here
    return (vm == null) 
      ? Text("User not logged in")
      : MyHomePage(user: vm.user) 
    ...                         
 
class Factory extends VmFactory<AppState, MyHomePageConnector, ViewModel> {   
  ViewModel? fromStore() { // 3. Nullable here
  return (state.user == null)
    ? null
    : ViewModel(user: state.user) 
  ...

Try running the: Null ViewModel Example.