从视图类获取绑定

Question

我有一个带有数据绑定布局的 CustomView 类，它接受一个变量。在包含 CustomView 的布局中，我想将一个属性传递给 CustomView，并让该 CustomView 将该属性传递给它自己的布局绑定。这是我所拥有的：

public class CustomView extends LinearLayout
{
public CustomView(Context inContext, AttributeSet inAttrs)
{
    super(inContext, inAttrs);

    inflate(inContext, R.layout.custom_view, null);
}



@BindingAdapter({"app:variable"})
public static void SetVariable(CustomView inCustomView, VariableType inMyVariable)
{
    CustomViewBinding binding = DataBindingUtil.getBinding(inCustomView);

    binding.setMyVariable(inMyVariable);
}
}

尝试从视图中提取绑定时会崩溃。这甚至可能吗？这是堆栈跟踪：

java.lang.NullPointerException: Attempt to invoke virtual method 'void xxx.databinding.CustomViewBinding.setVariableType(xxx.VariableType)' on a null object reference
                                                                            at xxx.CustomView.SetDynamicList(CustomView.java:32)
                                                                            at xxx.MyFragmentBinding.executeBindings(MyFragmentBinding.java:116)
                                                                            at android.databinding.ViewDataBinding.executePendingBindings(ViewDataBinding.java:350)
                                                                            at android.databinding.ViewDataBinding$6.run(ViewDataBinding.java:167)
                                                                            at android.databinding.ViewDataBinding$7.doFrame(ViewDataBinding.java:233)
                                                                            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:856)
                                                                            at android.view.Choreographer.doCallbacks(Choreographer.java:670)
                                                                            at android.view.Choreographer.doFrame(Choreographer.java:603)
                                                                            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
                                                                            at android.os.Handler.handleCallback(Handler.java:739)
                                                                            at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                            at android.os.Looper.loop(Looper.java:148)
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                            at java.lang.reflect.Method.invoke(Native Method)
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

如果我改变了

DataBindingUtil.getBinding(inCustomView)

到

DataBindingUtil.bind(inCustomView)

然后我明白了：

java.lang.IllegalArgumentException: View is not a binding layout
                                                                            at android.databinding.DataBindingUtil.bind(DataBindingUtil.java:166)
                                                                            at android.databinding.DataBindingUtil.bind(DataBindingUtil.java:140)
                                                                            at xxx.CustomView.SetDynamicList(CustomView.java:30)
                    -                                                        at xxx.databinding.MyFragmentBinding.executeBindings(MyFragmentBinding.java:116)
                                                                            at android.databinding.ViewDataBinding.executePendingBindings(ViewDataBinding.java:350)
                                                                            at android.databinding.ViewDataBinding$6.run(ViewDataBinding.java:167)
                                                                            at android.databinding.ViewDataBinding$7.doFrame(ViewDataBinding.java:233)
                                                                            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:856)
                                                                            at android.view.Choreographer.doCallbacks(Choreographer.java:670)
                                                                            at android.view.Choreographer.doFrame(Choreographer.java:603)
                                                                            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
                                                                            at android.os.Handler.handleCallback(Handler.java:739)
                                                                            at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                            at android.os.Looper.loop(Looper.java:148)
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                            at java.lang.reflect.Method.invoke(Native Method)
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这可能意味着布局文件未针对数据绑定进行格式化，但确实如此。它具有布局元素，以及带有变量和一切的数据元素。

Answer 1

您必须绑定膨胀视图才能创建数据绑定。在您的示例中，您正在绑定布局的 container。

您可以通过多种方式做到这一点。最简单的方法是将其绑定为通货膨胀的一部分：

public class CustomView extends LinearLayout
{
  CustomViewBinding mBinding;
  public CustomView(Context inContext, AttributeSet inAttrs)
  {
    super(inContext, inAttrs);
    LayoutInflater inflater = LayoutInflater.from(inContext);
    // I assume you want it inflated into this ViewGroup
    mBinding = CustomViewBinding.inflate(inflater, this, true);
  }

  public void setVariable(CustomView inCustomView, VariableType inMyVariable) {
    mBinding.setVariable(inMyVariable);
  }
  ...
}

除非您不希望将 setter 作为自定义视图的一部分，否则您实际上并不需要绑定适配器。在这种情况下，您仍然需要一种方法来获取绑定，因此您需要添加如下内容：

public CustomViewBinding getBinding() { return mBinding; }

以便您的绑定适配器工作。

如果您知道 LinearLayout 的内容都将来自膨胀视图，您可以使用这样的绑定适配器：

@BindingAdapter({"app:variable"})
public static void setVariable(CustomView inCustomView, VariableType inMyVariable)
{
    if (inCustomView.getChildCount() == 0) {
      return;
    }
    View boundView = inCustomView.getChildAt(0);
    CustomViewBinding binding = DataBindingUtil.getBinding(boundView);

    binding.setMyVariable(inMyVariable);
}

如果您的自定义视图不是很自定义，您可以直接包含您的布局：

<include layout="@layout/custom_view" app:variable="@{myVariableValue}"/>

当然，您必须将 LinearLayout 移动到 custom_view.xml 中。

Answer 2

基本上，这对我来说是这样的：

XML：

<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/containerView"
xmlns:tools="http://schemas.android.com/tools">

.....


</layout>

Java 类：

GeneralOverviewBinding binding = DataBindingUtil.bind((findViewById(R.id.containerView)));

这基本上返回给定布局根的绑定，如果不存在则创建一个绑定。