safeUnbox()不能反转 [英] safeUnbox() cannot be inverted
问题描述
我正试图消除我的Android应用程序的所有警告，其中之一是:
I'm trying to eliminate all the warnings of my Android application and one of them is this:
viewModel.value是一个装箱的字段，但需要取消装箱才能执行android:checked.这可能会导致NPE，因此数据绑定"将安全地将其拆箱.您可以更改表达式，并使用safeUnbox()显式包装viewModel.value以防止出现警告
viewModel.value is a boxed field but needs to be un-boxed to execute android:checked. This may cause NPE so Data Binding will safely unbox it. You can change the expression and explicitly wrap viewModel.value with safeUnbox() to prevent the warning
其中值是来自超类的通用ObservableField:
Where value is a generic ObservableField that comes from a super class:
public abstract class BaseDataTypeViewModel<T> extends BaseObservable {
public final ObservableField<T> value = new ObservableField<>();
...
}
并扩展为Boolean:
public class CheckBooleanDataTypeViewModel extends BaseDataTypeViewModel<Boolean> {
...
}
我在数据绑定-safeUnbox警告上看到发生警告，因为这是Boolean而不是boolean，因此我尝试添加以下内容:android:checked="@={safeUnbox(viewModel.value)}"而不是android:checked="@={viewModel.value}"，但是随后出现错误消息，提示我无法反转safeUnbox()方法.
I saw on data binding - safeUnbox warning that the warnings happen because this is a Boolean and not a boolean, so I tried to add this: android:checked="@={safeUnbox(viewModel.value)}" instead of android:checked="@={viewModel.value}" but then I got an error saying I can't invert the safeUnbox() method.
****/数据绑定错误**** msg:不能将表达式android.databinding.DynamicUtil.safeUnbox(viewModelValue)反转:方法safeUnbox没有反向，您必须在该接口上添加@InverseMethod批注表示在双向绑定表达式中使用哪种方法的方法
****/ data binding error ****msg:The expression android.databinding.DynamicUtil.safeUnbox(viewModelValue) cannot be inverted: There is no inverse for method safeUnbox, you must add an @InverseMethod annotation to the method to indicate which method should be used when using it in two-way binding expressions
我正确理解了两个分开的问题，但是我必须忍受警告以避免错误吗?或者它们是避免警告和错误的解决方案吗?它在说什么@InverseMethod呢?我没有设法添加此批注，因为该方法来自android包.
I understand correctly the 2 separated issues, but do I have to live with the warning to avoid the error or is their a solution to avoid both the warning and the error? What about the @InverseMethod it is talking about? I didn't manage to add this annotation because the method comes from the android package.
推荐答案
我没有以这种特定方式使用Android体系结构组件或数据绑定库，但我认为我仍然可以提供帮助.
I haven't worked with Android Architecture Components or with the Data Binding libraries in this particular way, but I think I can still help.
在您的XML中，您已经做到了:
Within your XML, you've got this:
android:checked="@={viewModel.value}"
系统正在向您发出警告，因为它希望您知道在viewModel.value为null的情况下，它会做一些特殊的事情(大概是false的行为).它是通过safeUnbox()方法完成的.
The system is giving you a warning because it wants you to know that in the case where viewModel.value is null, it's going to do something special (behave as though it were false instead, presumably). It does this via the safeUnbox() method.
要解决该警告，建议将safeUnbox()调用设为显式.您之所以不能这样做，是因为没有safeUnbox()的逆"可以将 从boolean返回到Boolean.
To solve the warning, it's suggesting making the safeUnbox() call explicit. You can't do that because there's no "inverse" of safeUnbox() to go back from boolean to Boolean.
但这听起来不像您必须使用safeUnbox()；您可以创建自己的将Boolean转换为boolean的方法，然后可以使用建议的注释来声明哪种方法将从boolean转换为Boolean.
But it doesn't sound like you have to use safeUnbox(); you could create your own method that converts Boolean to boolean, and then you could use the suggested annotation to declare which method will convert back from boolean to Boolean.
public class MyConversions {
@InverseMethod("myBox")
public static boolean myUnbox(Boolean b) {
return (b != null) && b.booleanValue();
}
public static Boolean myBox(boolean b) {
return b ? Boolean.TRUE : Boolean.FALSE;
}
}
现在您可以将XML更改为:
Now you can change your XML to:
android:checked="@={com.example.stackoverflow.MyConversions.myUnbox(viewModel.value)}"
我希望这会有所帮助.如果事实证明我离基地很远，请告诉我；我想了解更多有关此主题的信息.
I hope this helps. If it turns out that I'm way off-base, let me know; I'd love to learn more about this topic.
我从 https了解到的大部分内容://medium.com/google-developers/android-data-binding-inverse-functions-95aab4b11873
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