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

问题描述

是否有一种方法可以将其他参数传递给我的自定义AndroidViewModel构造函数，除了Application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，我会在片段中使用以下代码:

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其他参数String param传递到我的自定义ViewModel中.我只能传递应用程序上下文，而不能传递其他参数.我真的很感谢您的帮助.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.我希望现在会更好.

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

推荐答案

您需要为ViewModel创建一个工厂类.

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);
    }
}

当实例化视图模型时，您这样做:

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并使用工厂实例化覆盖getDefaultViewModelProviderFactory()，然后在没有工厂的情况下调用ViewModelProvider(this)或by viewModels().

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.

这篇关于Android ViewModel附加参数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！