斯卡拉的Android筛选器searchView窗口小部件“ gotClassCastException”

Question

我想在Scala插件eclipse中为Android创建“ searchView小部件”，这是我的代码，

 override def getFilter(): Filter = {
  new Filter() {

    protected override def publishResults(constraint: CharSequence, results: 
FilterResults) {
      var books = results.values.asInstanceOf[List[BookMetadata]]
      ItemAdapter.this.notifyDataSetChanged()
    }

    protected override def performFiltering(constraint: CharSequence): FilterResults = {

      val filteredResults = ListBuffer(books.asScala.toList.filter(b =>
        b.toString.startsWith(constraint.toString)): _*) .asInstanceOf[List[BookMetadata]]
      val results = new FilterResults()
      results.values = filteredResults
      results
    }
  }
}

我没有任何错误，但是当我运行程序时，我遇到了这个ClassCastException

这是我的日志：

 08-23 13:37:06.986: V/BookFragment(25407): query : modern
 08-23 13:37:06.996: W/Filter(25407): An exception occured during performFiltering()!
 08-23 13:37:06.996: W/Filter(25407): java.lang.ClassCastException:  
scala.collection.mutable.ListBuffer cannot be cast to java.util.List
08-23 13:37:06.996: W/Filter(25407):    at   
com.bitlit.android.BooksFragment$ItemAdapter$$anon$2.
performFiltering(BooksFragment.scala:138)
08-23 13:37:06.996: W/Filter(25407):    at 
android.widget.Filter$RequestHandler.handleMessage(Filter.java:234)

08-23 13:37:06.996: W/Filter(25407):    at   
android.os.Handler.dispatchMessage(Handler.java:99)

 08-23 13:37:06.996: W/Filter(25407): 
at android.os.Looper.loop(Looper.java:137)
08-23 13:37:06.996: W/Filter(25407): 
at android.os.HandlerThread.run(HandlerThread.java:61)

您能给我一些实施的提示吗

提前致谢！

Answer 1

看一下跟踪，似乎引起问题的行是这个：

val filteredResults = ListBuffer(books.asScala.toList.filter(b =>
    b.toString.startsWith(constraint.toString)): _*) .asInstanceOf[List[BookMetadata]]

您正在执行以下操作：

val filteredResults = ListBuffer(meta1, meta2).asInstanceOf[List[BookMetadata]]

所以ListBuffer[BookMetadata]不是List[BookMetadata]的实例。 无论您是指java.util.List还是scala不可变List 。

您可能可以执行以下操作：

import collection.JavaConverters._
val filteredResults = ListBuffer(/* ... */).asJava
// should return an instance of java.util.List