使用xpath为xml添加元素时,对象引用未设置为对象的实例

我有一个xml文件,并希望将一个子元素添加到其中一个节点,不知道为什么xpath会抛出null异常.这肯定是因为我可能给出了错误的xpath值.
这里添加元素的xpath是什么：

XPath我正在使用：

//SESSIONANALYSER/KER/MODES/NI/STATEINFORMATION[@TYPE='PREPAID']/INIT/INPUT

这是我想要添加子元素的地方：

<KER> 
    <MODES>
      <NI>
        <STATEINFORMATION TYPE="PREPAID">
          <INIT INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="LP6ACTIVATION">
             **<I have to add a child element here>**

在以下xml中：

<SESSIONANALYSER>
  <AP>
    <MODES>
      <NI>
        <STATEINFORMATION TYPE="PREPAID">
          <INIT INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="SLN7ACTIVATION">
              <METHOD NAME="CHECKSUBSCRIBERBALANCE" PARAMETERS="SLN7" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="SLN7" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="SLN7DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="SLN7" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="jk" PARAMETERS="k" POSSIBLEACTIONS1="k" MAINTAINSESSION="h" RESPONSE="l" NEXTLEVEL=";"></METHOD>
              <METHOD NAME="SENDMESSAGE" PARAMETERS="23" POSSIBLEACTIONS1="FALLOUTONSUCCESS" MAINTAINSESSION="yes" RESPONSE="format" NEXTLEVEL="msdfm"></METHOD>
              <METHOD NAME="payments" PARAMETERS="parametervalue" POSSIBLEACTIONS1="fg,f" MAINTAINSESSION="fdjfg89" RESPONSE="ndfgm" NEXTLEVEL="msdfm"></METHOD>
              <METHOD NAME="payments" PARAMETERS="l" POSSIBLEACTIONS1="l" MAINTAINSESSION="l" RESPONSE="l" NEXTLEVEL="l"></METHOD>
              <METHOD NAME="payments" PARAMETERS="l" POSSIBLEACTIONS1="l" MAINTAINSESSION="l" RESPONSE="l" NEXTLEVEL="l"></METHOD>
              <METHOD NAME="payments" PARAMETERS="k" POSSIBLEACTIONS1="k" MAINTAINSESSION="k" RESPONSE="k" NEXTLEVEL="k"></METHOD>
              <METHOD NAME="payments" PARAMETERS="L" POSSIBLEACTIONS1="L" MAINTAINSESSION="L" RESPONSE="L" NEXTLEVEL="L"></METHOD>
              <METHOD NAME="SENDMESSAGE" PARAMETERS="23" POSSIBLEACTIONS1="FALLOUTONSUCCESS" MAINTAINSESSION="yes" RESPONSE="format" NEXTLEVEL="msdfm"></METHOD>
              <METHOD NAME="payments" PARAMETERS="12" POSSIBLEACTIONS1="FALLOUTONSUCCESS" MAINTAINSESSION="yes" RESPONSE="format" NEXTLEVEL="msvm"></METHOD>
              <METHOD NAME="SENDMESSAGE" PARAMETERS="23" POSSIBLEACTIONS1="FALLOUTONSUCCESS" MAINTAINSESSION="yes" RESPONSE="0" NEXTLEVEL="3"></METHOD>
              <METHOD NAME="SENDMESSAGE" PARAMETERS="23" POSSIBLEACTIONS1="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="format" NEXTLEVEL="3"></METHOD>
            </INPUT>
          </INIT>
          <FAILUREREGION INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="LOWBALANCE">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="1" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="SETPSOFAILED">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="2" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="UCIPDEBIT">
              <METHOD NAME="UNSETPSOINMINSAT" PARAMETERS="SLN7" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_UNSETPSO_FALSE" MAINTAINSESSION="NO" RESPONSE="-6" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="3" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="UNSETPSO">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="4" NEXTLEVEL="" />
            </INPUT>
          </FAILUREREGION>
        </STATEINFORMATION>
        <STATEINFORMATION TYPE="POSTPAID">
          <INIT INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="SLN7DEACTIVATION">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="5" NEXTLEVEL="" />
            </INPUT>
          </INIT>
        </STATEINFORMATION>
      </NI>
    </MODES>
  </AP>
  <TN>
    <MODES>
      <NI>
        <STATEINFORMATION TYPE="PREPAID">
          <INIT INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="LPC16ACTIVATION">
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LPC16" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LP26ACTIVATION">
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LP26" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LP49ACTIVATION">
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LP49" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LPT16ACTIVATION">
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LPT16" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LP60ACTIVATION">
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LP60" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LPC16DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LPC16" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LP26DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LP26" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <!--<METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />-->
            </INPUT>
            <INPUT VALUE="LP49DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LP49" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LPT16DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LPT16" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LP60DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LP60" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
          </INIT>
          <FAILUREREGION INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="LOWBALANCE">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="1" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="SETPSOFAILED">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="2" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="UCIPDEBIT">
              <METHOD NAME="UNSETPSOINMINSAT" PARAMETERS="SLN7" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_UNSETPSO_FALSE" MAINTAINSESSION="NO" RESPONSE="-6" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="3" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="UNSETPSO">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="4" NEXTLEVEL="" />
            </INPUT>
          </FAILUREREGION>
        </STATEINFORMATION>
        <STATEINFORMATION TYPE="POSTPAID">
          <INIT INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="5" NEXTLEVEL="" />
            </INPUT>
          </INIT>
        </STATEINFORMATION>
      </NI>
    </MODES>
  </TN>
  <KER>
    <MODES>
      <NI>
        <STATEINFORMATION TYPE="PREPAID">
          <INIT INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="LP6ACTIVATION">
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LP6" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LPSP15ACTIVATION">
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LPSP15" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LP6DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LP6" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LPSP15DEACTIVATION">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LPSP15" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="LP6SUBSCRIPTION">
              <METHOD NAME="CHECKSUBSCRIBERBALANCE" PARAMETERS="LP6" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_LOWBALANCE_INSUFFICIENTBALANCE" MAINTAINSESSION="NO" RESPONSE="-3" NEXTLEVEL="" />
              <METHOD NAME="SETPSOINUCIP" PARAMETERS="LP6" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="FIREUCIPDEBIT" PARAMETERS="LP6" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_CHARGINGFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="0" NEXTLEVEL="" />
            </INPUT>
          </INIT>
          <FAILUREREGION INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="LOWBALANCE">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="1" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="CHARGINGFAILED">
              <METHOD NAME="UNSETPSOINUCIP" PARAMETERS="LP6" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_SETPSOFAILED_FALSE" MAINTAINSESSION="NO" RESPONSE="-4" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="6" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="SETPSOFAILED">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="2" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="UCIPDEBIT">
              <METHOD NAME="UNSETPSOINMINSAT" PARAMETERS="SLN7" POSSIBLEACTIONS="FALLOUTON_FAILUREREGION_UNSETPSO_FALSE" MAINTAINSESSION="NO" RESPONSE="-6" NEXTLEVEL="" />
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="3" NEXTLEVEL="" />
            </INPUT>
            <INPUT VALUE="UNSETPSO">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="4" NEXTLEVEL="" />
            </INPUT>
          </FAILUREREGION>
        </STATEINFORMATION>
        <STATEINFORMATION TYPE="POSTPAID">
          <INIT INVALIDINPUTRESPONSE="-2">
            <INPUT VALUE="">
              <METHOD NAME="SENDMESSAGE" PARAMETERS="" POSSIBLEACTIONS="FALLOUTONSUCCESS" MAINTAINSESSION="NO" RESPONSE="5" NEXTLEVEL="" />
            </INPUT>
          </INIT>
        </STATEINFORMATION>
      </NI>
    </MODES>
  </KER>
</SESSIONANALYSER>

您正在评估的XPath表达式：

//SESSIONANALYSER/KER/MODES/NI/STATEINFORMATION[@TYPE='PREPAID']/INIT/INPUT

不只选择一个而是选择六个INPUT元素.

您指定要在第一个元素之后添加新元素.

因此,使用此XPath表达式,它只选择一个(想要的)INPUT元素：

(//SESSIONANALYSER/KER/MODES/NI/STATEINFORMATION[@TYPE='PREPAID']/INIT/INPUT)[1]

大多数XPath引擎提供了一个SelectNodes()方法,它返回NodeList中的选定节点,程序员需要遍历此集合 – 即使只选择了一个节点 – 请记住这一点.