如何使用 Fragment 进行数据绑定

Question

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

除了我试图将数据竞价应用于片段，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 的片段如下所示：

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

onCreateView 的片段如下所示：

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

片段的部分布局文件如下所示：

<?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 不知道它应该绑定哪个布局文件 - 因此出现错误。有什么建议吗？

Answer 1

数据绑定实现必须在fragment的onCreateView方法中，删除你的OnCreate方法中存在的任何数据绑定， 你的onCreateView 应该是这样的：

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;
}

Answer 2

实际上鼓励您使用生成的 Binding 的 inflate 方法，而不是 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();
}

Docs for DataBindingUtil.inflate():

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

Answer 3

即使其他答案也可能效果很好，但我想告诉最好的方法。

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

一种选择是通过DataBindingUtil 膨胀但只有当您不知道已生成绑定类时。

--您已经自动生成了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 Kotlin 中

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documentation中可以看到。

膨胀

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

仅当 layoutId 事先未知时才使用此版本。否则，使用生成的 Binding 的 inflate 方法来确保类型安全 通货膨胀。

如果你的布局绑定类没有生成@See this answer。

Answer 4

如果您使用的是 ViewModel 和 LiveData，这样的语法就足够了

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
}

Answer 5

正如大多数人所说，但不要忘记设置 LifeCycleOwner
Java 中的示例 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();
}

Answer 6

在 Android 数据绑定中试试这个

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;
}

Answer 7

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
}

Answer 8

如下所述，可以简单地检索视图对象

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;

}

Answer 9

数据绑定Fragments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);

    }
}

Answer 10

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();
}

Answer 11

我一直在为我的申请寻找答案，这里是 Kotlin 语言的答案。

private lateinit var binding: FragmentForgetPasswordBinding

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?): View? {
    binding=DataBindingUtil.inflate(inflater,R.layout.fragment_forget_password,container,false)
    
    val viewModel=ViewModelProvider(this).get(ForgetPasswordViewModel::class.java)
    binding.recoveryViewModel=viewModel
    viewModel.forgetPasswordInterface=this
    return binding.root
}

Answer 12

Kotlin 中的另一个例子：

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”，那么正确的名称应该是 MartianDataBinding。

Answer 13

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 中像这样声明绑定 val：

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

别忘了把这个写在片段里

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

Answer 14

在 kotlin 中你可以这样做：

//Pass the layout as parameter to the fragment constructor    
class SecondFragment : Fragment(R.layout.fragment_second) {

    private var _binding: FragmentSecondBinding? = null
    private val binding  get() = _binding!!

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        _binding = FragmentSecondBinding.bind(view)  //if the view is already inflated then we can just bind it to view binding.

    }

    //Note: Fragments outlive their views. Make sure you clean up any references to the binding class
    // instance in the fragment's onDestroyView() method.
    override fun onDestroyView() {
        Toast.makeText(activity, "On destroy", Toast.LENGTH_SHORT).show()
        super.onDestroyView()
        _binding = null
    }
}

您可以从您的布局中访问视图元素，例如：

binding.tvName.text = "Messi"

其中 tvName 是视图元素的 id。

Answer 15

每个人都说inflate()，但如果我们想在onViewCreated() 中使用它呢？

您可以使用具体绑定类的bind(view)方法获取view的ViewDataBinding实例。

通常我们这样写BaseFragment（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 Fragment 都使用数据绑定，您甚至可以使用类型参数使其更简单。

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空是可以的，但是..你明白了。如果你希望它可以为空，你可以这样做。