从视图类获取绑定

2024-06-28

我有一个 CustomView 类,其数据绑定布局采用变量。在包含 CustomView 的布局中,我想将一个属性传递到 CustomView 中,并让该 CustomView 将该属性传递到其自己的布局的绑定中。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)

to

DataBindingUtil.bind(inCustomView)

然后我得到这个:

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,但事实确实如此。它具有布局元素、带有变量的数据元素和所有内容。


您必须绑定膨胀视图才能创建数据绑定。在您的示例中,您正在绑定容器的布局。

您可以通过多种方式做到这一点。最简单的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);
  }
  ...
}

您实际上并不需要绑定适配器,除非您不希望设置器作为自定义视图的一部分。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; }

这样你的绑定适配器就可以工作了。

如果您知道 LinearLayout 内容全部来自膨胀视图,则可以使用如下绑定适配器:

@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非常自定义,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 移至 custom_view.xml 中。

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