Question

我试图通过定位索引来显示选择框的第一个选择项，selected =“index == 0”，如下所示，但这没有成功。我该如何做到这一点？

<div class="col-md-12 col-lg-4">
    <select class="pull-right border-outset3 p-a-pt5 w-15" [(ngModel)]="sortValue"
      (change)="sortProducts()">
      <optgroup label="Sort By:">
        <option *ngFor="let menu of sortMenu$ | async; let ndx=index"
          value="{{menu.value}}" selected="ndx==0">
          {{menu.label}}
        </option>
      </optgroup>
    </select>
  </div>

Answer 1

您可以定义Observable的修改版本（例如scala> result.show 2018-05-20 17:08:54 ERROR Executor:91 - Exception in task 0.0 in stage 1.0 (TID 1) java.lang.RuntimeException: Error while encoding: java.lang.RuntimeException: java.lang.String is not a valid external type for schema of int if (assertnotnull(input[0, org.apache.spark.sql.Row, true]).isNullAt) null else validateexternaltype(getexternalrowfield(assertnotnull(input[0, org.apache.spark.sql.Row, true]), 0, time_id), IntegerType) AS time_id#23 if (assertnotnull(input[0, org.apache.spark.sql.Row, true]).isNullAt) null else validateexternaltype(getexternalrowfield(assertnotnull(input[0, org.apache.spark.sql.Row, true]), 1, week), IntegerType) AS week#24 if (assertnotnull(input[0, org.apache.spark.sql.Row, true]).isNullAt) null else validateexternaltype(getexternalrowfield(assertnotnull(input[0, org.apache.spark.sql.Row, true]), 2, month), IntegerType) AS month#25 if (assertnotnull(input[0, org.apache.spark.sql.Row, true]).isNullAt) null else staticinvoke(class org.apache.spark.unsafe.types.UTF8String, StringType, fromString, validateexternaltype(getexternalrowfield(assertnotnull(input[0, org.apache.spark.sql.Row, true]), 3, calendar), StringType), true, false) AS calendar#26 at org.apache.spark.sql.catalyst.encoders.ExpressionEncoder.toRow(ExpressionEncoder.scala:291) at org.apache.spark.sql.SparkSession$$anonfun$4.apply(SparkSession.scala:589) at org.apache.spark.sql.SparkSession$$anonfun$4.apply(SparkSession.scala:589) at scala.collection.Iterator$$anon$11.next(Iterator.scala:409) at scala.collection.Iterator$$anon$11.next(Iterator.scala:409) at org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage1.processNext(Unknown Source) at org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43) at org.apache.spark.sql.execution.WholeStageCodegenExec$$anonfun$10$$anon$1.hasNext(WholeStageCodegenExec.scala:614) at org.apache.spark.sql.execution.SparkPlan$$anonfun$2.apply(SparkPlan.scala:253) at org.apache.spark.sql.execution.SparkPlan$$anonfun$2.apply(SparkPlan.scala:247) at org.apache.spark.rdd.RDD$$anonfun$mapPartitionsInternal$1$$anonfun$apply$25.apply(RDD.scala:830) at org.apache.spark.rdd.RDD$$anonfun$mapPartitionsInternal$1$$anonfun$apply$25.apply(RDD.scala:830) at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38) at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:324) at org.apache.spark.rdd.RDD.iterator(RDD.scala:288) at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38) at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:324) at org.apache.spark.rdd.RDD.iterator(RDD.scala:288) at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:87) at org.apache.spark.scheduler.Task.run(Task.scala:109) at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:345) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.RuntimeException: java.lang.String is not a valid external type for schema of int at org.apache.spark.sql.catalyst.expressions.GeneratedClass$SpecificUnsafeProjection.If$(Unknown Source) at org.apache.spark.sql.catalyst.expressions.GeneratedClass$SpecificUnsafeProjection.apply(Unknown Source) at org.apache.spark.sql.catalyst.encoders.ExpressionEncoder.toRow(ExpressionEncoder.scala:288)），其中使用sortMenuDefault运算符将第一项的值分配给sortValue：

do

并在模板中使用Observable：

this.sortMenuDefault = this.sortMenu$.do(items => {
  if (!this.sortValue && items && items.length > 0) {
    this.sortValue = items[0].value;
  }
});

请参阅this stackblitz了解演示。

Angular：如何动态选择select组件的第一项

1 个答案: