Question

是否有一种简洁的方法来仅获取child added或任何事件？现在，我必须执行以下操作，看起来很愚蠢

ref.addChildEventListener(object : ChildEventListener {
    override fun onCancelled(p0: DatabaseError) {}
    override fun onChildChanged(p0: DataSnapshot, p1: String?) {}
    override fun onChildMoved(p0: DataSnapshot, p1: String?) {}
    override fun onChildRemoved(p0: DataSnapshot) {}
    override fun onChildAdded(p0: DataSnapshot, p1: String?) {
        subscriber.onNext(Value.parse(unitName, varName, p0))
    }
})

Answer 1

您可以创建自己的抽象类，该抽象类实现ChildEventListener，但不提供onChildAdded的实现：

abstract class ChildAddedEventListener : ChildEventListener {
    override fun onCancelled(p0: DatabaseError) {
    }

    override fun onChildMoved(p0: DataSnapshot, p1: String?) {
    }

    override fun onChildChanged(p0: DataSnapshot, p1: String?) {
    }

    override fun onChildRemoved(p0: DataSnapshot) {
    }
}

然后，您将ChildAddedEventListener子类化，并仅提供所需的实现：

class MyChildAddedEventListener: ChildAddedEventListener {
    override fun onChildAdded(p0: DataSnapshot, p1: String?) {
        // your code here
    }
}

有了它，您可以在将其添加到查询中时将其用作内联对象表达式：

query.addChildEventListener(object : ChildAddedEventListener() {
    override fun onChildAdded(p0: DataSnapshot, p1: String?) {
        subscriber.onNext(Value.parse(unitName, varName, p0))
    }
})

Answer 2

在您的情况下，通常省略所有方法的模式的名称称为Adapter：

$recruits

（接口）适配器类是使用空方法实现接口的类，因此您可以选择要覆盖的那个

Answer 3

您可以

object EmptyChildEventListener : ChildEventListener {
     override fun onCancelled(p0: DatabaseError) {}
     override fun onChildChanged(p0: DataSnapshot, p1: String?) {}
     override fun onChildMoved(p0: DataSnapshot, p1: String?) {}
     override fun onChildRemoved(p0: DataSnapshot) {}
     override fun onChildAdded(p0: DataSnapshot, p1: String?) { }
} 

ref.addChildEventListener(object : ChildEventListener by EmptyChildEventListener {
     override fun onChildAdded(p0: DataSnapshot, p1: String?) {
         subscriber.onNext(Value.parse(unitName, varName, p0))
     }
})

编辑：，但是您可以像这样改善它

inline fun DatabaseReference.onChildAdded(crossinline added: (DataSnapshot, String?) -> Unit) {
    this.addChildEventListener(object : ChildEventListener by EmptyChildEventListener {
         override fun onChildAdded(p0: DataSnapshot, p1: String?) = added(p0, p1)
    })
})

现在您可以做

ref.onChildAdded { p0, p1 -> 
    subscriber.onNext(Value.parse(unitName, varName, p0))
}

收听单个事件的简洁方式

3 个答案: