验证if子句中的空查询

Question

我有一个简单的Linq查询，并且if...else条件类似：

var incidenciaPronosticada = _c.IncidenciaPronosticadas

    .Where( x => x.IdIncidenciaPronosticada == item.IdIncidenciaPronosticada )

    .FirstOrDefault();

if( incidenciaPronosticada.IdIncidenciaPronosticada != 0 || incidenciaPronosticada.IdIncidenciaPronosticada != null )

{

    //code there

}

else {

    //code there

}

问题是当incidenciaPronosticada它为null时不执行else子句，它只是停止

incidenciaPronosticada.IdIncidenciaPronosticada ='incidenciaPronosticada.IdIncidenciaPronosticada'引发了类型'System.NullReferenceException'的异常

为什么不读incidenciaPronosticada.IdIncidenciaPronosticada != null？如果调试器读取了它，它应该传递给else子句否？还是我做错了什么？问候

Answer 1

incidenciaPronosticada本身可以为null，这incidenciaPronosticada.IdIncidenciaPronosticada != 0将导致aNullReferenceExecption因为IdIncidenciaPronosticada无法访问。执行显式的null检查或使用null安全导航操作符?.：if( incidenciaPronosticada != null && incidenciaPronosticada.IdIncidenciaPronosticada != 0 ) {或者：if( incidenciaPronosticada?.IdIncidenciaPronosticada > 0 ) {（请注意我用的> 0，而不是!= 0因为> 0会true如果incidenciaPronosticada是空的（因为(Int32?)null != (Int32?)0）：还要注意，incidenciaPronosticada?.IdIncidenciaPronosticada表达式的类型是Nullable<Int32>（aka Int32?）而不是Int32。这是下表的结果 if( incidenciaPronosticada.IdIncidenciaPronosticada ... )incidenciaPronosticada&nbsp; &nbsp; &nbsp; IdIncidenciaPronosticada&nbsp; &nbsp; . != 0&nbsp; &nbsp; . > 0null&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; null&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; throws&nbsp; &nbsp; throws(object)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; null&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; true&nbsp; &nbsp; &nbsp; false(object)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;false&nbsp; &nbsp; &nbsp;false(object)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;true&nbsp; &nbsp; &nbsp; true这是下表的结果 if( incidenciaPronosticada?.IdIncidenciaPronosticada ... )incidenciaPronosticada&nbsp; &nbsp; &nbsp; IdIncidenciaPronosticada&nbsp; &nbsp; ?. != 0&nbsp; &nbsp;?. > 0null&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; null&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; true&nbsp; &nbsp; &nbsp; false(object)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; null&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; true&nbsp; &nbsp; &nbsp; false(object)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;false&nbsp; &nbsp; &nbsp;false(object)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;true&nbsp; &nbsp; &nbsp; true

Answer 2

您正在尝试访问incidenciaPronosticada内部的成员。空支票应该看起来像if(incidenciaPronosticada != null){//code there}else {//code there}