Android ViewModel 附加参数 [英] Android ViewModel additional arguments

问题描述

有没有办法将附加参数传递给我的自定义 AndroidViewModel 构造函数，除了应用程序上下文.示例:

Is there a way to pass additional argument to my custom AndroidViewModel constructor except Application context. Example:

public class MyViewModel extends AndroidViewModel {
    private final LiveData<List<MyObject>> myObjectList;
    private AppDatabase appDatabase;

    public MyViewModel(Application application, String param) {
        super(application);
        appDatabase = AppDatabase.getDatabase(this.getApplication());

        myObjectList = appDatabase.myOjectModel().getMyObjectByParam(param);
    }
}

当我想使用我的自定义 ViewModel 类时，我会在片段中使用此代码:

And when I want to user my custom ViewModel class I use this code in my fragment:

MyViewModel myViewModel = ViewModelProvider.of(this).get(MyViewModel.class)

所以我不知道如何将附加参数 String param 传递到我的自定义 ViewModel 中.我只能传递应用程序上下文，而不能传递附加参数.我真的很感激任何帮助.谢谢你.

So I don't know how to pass additional argument String param into my custom ViewModel. I can only pass Application context, but not additional arguments. I would really appreciate any help. Thank you.

我添加了一些代码.我希望现在好点了.

I've added some code. I hope it's better now.

推荐答案

你的 ViewModel 需要有一个工厂类.

You need to have a factory class for your ViewModel.

public class MyViewModelFactory implements ViewModelProvider.Factory {
    private Application mApplication;
    private String mParam;


    public MyViewModelFactory(Application application, String param) {
        mApplication = application;
        mParam = param;
    }


    @Override
    public <T extends ViewModel> T create(Class<T> modelClass) {
        return (T) new MyViewModel(mApplication, mParam);
    }
}

在实例化视图模型时，您可以这样做:

And when instantiating the view model, you do like this:

MyViewModel myViewModel = ViewModelProvider(this, new MyViewModelFactory(this.getApplication(), "my awesome param")).get(MyViewModel.class);

对于 kotlin，您可以使用委托属性:

For kotlin, you may use delegated property:

val viewModel: MyViewModel by viewModels { MyViewModelFactory(getApplication(), "my awesome param") }

还有另一个新选项 - 实现 HasDefaultViewModelProviderFactory 并使用工厂的实例化覆盖 getDefaultViewModelProviderFactory()，然后调用 ViewModelProvider(this) 或 by viewModels() 没有工厂.

There's also another new option - to implement HasDefaultViewModelProviderFactory and override getDefaultViewModelProviderFactory() with the instantiation of your factory and then you would call ViewModelProvider(this) or by viewModels() without the factory.

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