如何在Fragment中使用数据绑定

我正在尝试遵循Google官方文档中的数据绑定示例 https://developer.android.com/tools/data-binding/guide.html中的

除了我试图将数据出价应用于片段，而不是活动。

我目前在编译时遇到的错误是

Error:(37, 27) No resource type specified (at 'text' with value '@{marsdata.martianSols}.

onCreate 片段看起来像这样：

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    MartianDataBinding binding = MartianDataBinding.inflate(getActivity().getLayoutInflater());
    binding.setMarsdata(this);
}

onCreateView 片段看起来像这样：

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.martian_data, container, false);
}

布局文件的片段部分如下所示：

<?xml version="1.0" encoding="utf-8"?>

<layout xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
        <variable
            name="marsdata"
            type="uk.co.darkruby.app.myapp.MarsDataProvider" />
    </data>
...

        <TextView
            android:layout_height="wrap_content"
            android:layout_width="wrap_content"
            android:text="@{marsdata.martianSols}"
        />

    </RelativeLayout>
</layout>

我的怀疑是MartianDataBinding不知道应该绑定哪个布局文件-因此出错。有什么建议？

数据绑定实现必须在该onCreateView片段的方法中，删除您的OnCreate方法中存在的任何数据绑定，您onCreateView应如下所示：

public View onCreateView(LayoutInflater inflater, 
                         @Nullable ViewGroup container, 
                         @Nullable Bundle savedInstanceState) {
    MartianDataBinding binding = DataBindingUtil.inflate(
            inflater, R.layout.martian_data, container, false);
    View view = binding.getRoot();
    //here data must be an instance of the class MarsDataProvider
    binding.setMarsdata(data);
    return view;
}

实际上，建议您使用inflate生成的Binding 的方法，而不要使用DataBindingUtil：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    MainFragmentBinding binding = MainFragmentBinding.inflate(inflater, container, false);
    //set variables in Binding
    return binding.getRoot();
}

DataBindingUtil.inflate（）的文档：

仅在预先未知layoutId时才使用此版本。否则，请使用生成的Binding的inflate方法来确保类型安全的膨胀。

甚至其他答案也可能效果很好，但我想告诉您最佳方法。

Binding class's inflate按照Android文档中的建议使用。

一种选择是充气，DataBindingUtil 但只有在您不知道已生成绑定类时，才进行充气。

-您已自动生成binding class，请使用该类而不是使用DataBindingUtil。

在Java中

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    HomeFragmentBinding binding = HomeFragmentBinding.inflate(inflater, container, false);
    //set binding variables here
    return binding.getRoot();
}

在科特林

lateinit var binding: HomeFragmentBinding 
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    binding = HomeFragmentBinding.inflate(inflater, container, false)
    return binding.root
}

在DataBindingUtil类文档中，您可以看到。

膨胀

T inflate (LayoutInflater inflater, 
                int layoutId, 
                ViewGroup parent, 
                boolean attachToParent)

仅在预先未知layoutId时才使用此版本。否则，请使用生成的Binding的inflate方法来确保类型安全的膨胀。

如果未生成布局biniding类，请参见@ 答案。

如果您使用的是ViewModel和LiveData，这是足够的语法

Kotlin语法：

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    return MartianDataBinding.inflate(
        inflater,
        container,
        false
    ).apply {
        lifecycleOwner = viewLifecycleOwner
        vm = viewModel    // Attach your view model here
    }.root
}

在Android DataBinding中尝试一下

FragmentMainBinding binding;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        binding = DataBindingUtil.inflate(inflater, R.layout.fragment_main, container, false);
        View rootView = binding.getRoot();
        initInstances(savedInstanceState);
        return rootView;
}

只需按如下所述检索视图对象

public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

View view = DataBindingUtil.inflate(inflater, R.layout.layout_file, container, false).getRoot();

return view;

}

Kotlin语法：

lateinit var binding: MartianDataBinding
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    binding = DataBindingUtil.inflate(inflater, R.layout.martian_data, container, false)
    return binding.root
}

就像大多数人所说的，但不要忘记在Java中设置LifeCycleOwner
Sample， 即

public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    super.onCreateView(inflater, container, savedInstanceState);
    BindingClass binding = DataBindingUtil.inflate(inflater, R.layout.fragment_layout, container, false);
    ModelClass model = ViewModelProviders.of(getActivity()).get(ViewModelClass.class);
    binding.setLifecycleOwner(getActivity());
    binding.setViewmodelclass(model);

    //Your codes here

    return binding.getRoot();
}

在我的代码中工作。

private FragmentSampleBinding dataBiding;
private SampleListAdapter mAdapter;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    super.onCreateView(inflater, container, savedInstanceState);
    dataBiding = DataBindingUtil.inflate(inflater, R.layout.fragment_sample, null, false);
    return mView = dataBiding.getRoot();
}

数据绑定片段的完整示例

FragmentMyProgramsBinding是为res / layout / fragment_my_programs生成的绑定类

public class MyPrograms extends Fragment {
    FragmentMyProgramsBinding fragmentMyProgramsBinding;

    public MyPrograms() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
    FragmentMyProgramsBinding    fragmentMyProgramsBinding = DataBindingUtil.inflate(inflater, R
                .layout.fragment_my_programs, container, false);
        return fragmentMyProgramsBinding.getRoot();
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

    }
}

关于数据绑定的非常有用的博客：https : //link.medium.com/HQY2VizKO1

class FragmentBinding<out T : ViewDataBinding>(
    @LayoutRes private val resId: Int
) : ReadOnlyProperty<Fragment, T> {

    private var binding: T? = null

    override operator fun getValue(
        thisRef: Fragment,
        property: KProperty<*>
    ): T = binding ?: createBinding(thisRef).also { binding = it }

    private fun createBinding(
        activity: Fragment
    ): T = DataBindingUtil.inflate(LayoutInflater.from(activity.context),resId,null,true)
}

在Fragment中这样声明绑定val：

private val binding by FragmentBinding<FragmentLoginBinding>(R.layout.fragment_login)

不要忘了把它写成片段

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    return binding.root
}

Kotlin中的另一个示例：

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val binding = DataBindingUtil
            .inflate< MartianDataBinding >(
                    inflater,
                    R.layout.bla,
                    container,
                    false
            )

    binding.modelName = // ..

    return binding.root
}

请注意，名称“ MartianDataBinding”取决于布局文件的名称。如果文件名为“ martian_data”，则正确的名称将为MartianDataBinding。

每个人都在谈论inflate()，但是如果我们要使用它onViewCreated()呢？

您可以使用bind(view)具体绑定类的方法来获取ViewDataBinding实例view。

通常，我们将BaseFragment编写如下（简化）：

// BaseFragment.kt
abstract fun layoutId(): Int

override fun onCreateView(inflater, container, savedInstanceState) = 
    inflater.inflate(layoutId(), container, false)

并在子片段中使用它。

// ConcreteFragment.kt
override fun layoutId() = R.layout.fragment_concrete

override fun onViewCreated(view, savedInstanceState) {
    val binding = FragmentConcreteBinding.bind(view)
    // or
    val binding = DataBindingUtil.bind<FragmentConcreteBinding>(view)
}

如果所有Fragments都使用数据绑定，则甚至可以使用type参数使其更简单。

abstract class BaseFragment<B: ViewDataBinding> : Fragment() {
    abstract fun onViewCreated(binding: B, savedInstanceState: Bundle?)

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        onViewCreated(DataBindingUtil.bind<B>(view)!!, savedInstanceState)
    }
}

我不知道在那里断言非null是可以的，但是..你明白了。如果您希望它可以为空，则可以这样做。