什么是；foo？.bar“；你是说Groovy？ #{if adsonuiasetlist.size（）>0} #{列表项：ADSONUIASETLIST，as:'adsonui'} 资产：${adsonui？.productname}（${adsonui？.AssetId}）广告客户：${adsonui？.campaign.Advertiser.contact_person}（${adsonui？.campaign.Advertiser.id}）

#{/list} #{/if}

---

有人能解释一下${adsonui？.productname}代表什么吗？。请告诉我groovy和play framework pelase的新功能。如果

adsonui

不为空，则${adsonui？.productname}将返回

adsonui.productname

或

null

如果为null

---

它叫

？允许在foo为空时避免NPE异常

请参阅axample-第一个println为null，第二个失败

#{if adsonuiAssetList.size()>0}
    #{list items:adsonuiAssetList, as:'adsonui'}
        <div class="imageElement">
            <h3>Asset : ${adsonui?.productname}(${adsonui?.AssetId})&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Advertiser : ${adsonui?.campaign.advertiser.contact_person}(${adsonui?.campaign.advertiser.id})</h3>
            <p></p>
            <a href="@{Assets.showAssetDetails()}?assetid=${adsonui?.AssetId}"  title="${adsonui?.productname}" class="open"></a>
            <img src="@{Assets.getAssetFileForSlideShow(adsonui?.AssetId,adsonui?.campaign?.mode_of_advertisement,870,240)}"  alt="${adsonui?.productname}" class="full" />
            <img src="@{Assets.getAssetFileForSlideShow(adsonui?.AssetId,adsonui?.campaign?.mode_of_advertisement,150,150)}"  alt="${adsonui?.productname}" class="thumbnail" />
    </div>
    #{/list}
#{/if}

---

也就是说，您不需要测试foo是否为空，并决定是否可以使用参考条

Thank you@Marmite Bomber

def foo

println foo?.bar

null

println foo.bar

Caught: java.lang.NullPointerException: Cannot get property 'bar' on null object