android - 从 View 类中获取绑定(bind)

Question

我有一个带有数据绑定(bind)布局的 CustomView 类，该布局采用变量。在包含 CustomView 的布局中，我想将一个属性传递给 CustomView，并让 CustomView 将该属性传递给它自己的布局绑定(bind)。这是我拥有的:

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 View 中提取绑定(bind)时会崩溃。这可能吗？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

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没有为数据绑定(bind)格式化，但确实如此。它具有布局元素，以及带有变量和所有内容的数据元素。

Answer 1

您必须绑定(bind)膨胀 View 才能创建数据绑定(bind)。在您的示例中，您绑定(bind)了布局的容器。

您可以通过多种方式做到这一点。最简单的是将其绑定(bind)为 inflation 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 setter 作为自定义 View 的一部分，否则您实际上并不需要绑定(bind)适配器。在这种情况下，您仍然需要一种方法来获取绑定(bind)，因此您需要添加如下内容:

public CustomViewBinding getBinding() { return mBinding; }

这样你的绑定(bind)适配器就可以工作了。

如果您知道 LinearLayout 内容都将来自膨胀 View ，您可以使用这样的绑定(bind)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 View 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。