FeatureClass.Search(IQuery Filter,bool Recycling)參數(shù)說明
2011-07-19 8:32
IFeatureClass的Search方法大家經(jīng)常用到，很多人對(duì)Search方法的其中一個(gè)參數(shù)bool Recycling不是很理解。目前網(wǎng)上關(guān)于這個(gè)參數(shù)的意義的解釋有兩個(gè)版本：1.第一版本是Isnotnull大牛的：http://bbs.esrichina-bj.cn/ESRI/viewthread.php?tid=13461他提出的觀點(diǎn)的是：參數(shù)Recycling為True的時(shí)候是傳引用，為False的時(shí)候?yàn)閭髦?/span>
2.第二個(gè)版本是Echo兄的：
http://gis.cnblogs.com/home.aspx?page=3
他提出的觀點(diǎn)是：參數(shù)Recycling為True的時(shí)候游標(biāo)對(duì)象(Ifeaturecursor)是只包含一條記錄,為False的時(shí)候游標(biāo)對(duì)象(Ifeaturecursor)為10條記錄（假設(shè)Featureclass有10條記錄）
我經(jīng)過測(cè)試提出個(gè)人的觀點(diǎn)：
1.pFeatureCursor存儲(chǔ)的是所有符合條件的Feature對(duì)象的引用，
2.Recycling的意思是回收，參數(shù)Recycling為True的時(shí)當(dāng)執(zhí)行這個(gè)方法IFeature pFeature=pFeatureCursor.NextFeature()上一條記錄的值在內(nèi)存中所占的地址就會(huì)被銷毀回收，為False的時(shí)候當(dāng)執(zhí)行這個(gè)方法IFeature pFeature=pFeatureCursor.NextFeature()上一條記錄的值依然存在在內(nèi)存中。
Ok，接下來以實(shí)例證明本觀點(diǎn)：
1.參數(shù)Recycling設(shè)置為True
IFeatureClass pFeatureClass = (this.axMapControl1.get_Layer(0) as IFeatureLayer).FeatureClass;
IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, true);
//IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, false);
List<IFeature> pFeatures = new List<IFeature>();
IFeature pFeature = pFeatureCursor.NextFeature();
while (pFeature != null)
{
pFeatures.Add(pFeature);
pFeature = pFeatureCursor.NextFeature();
}
for (int i = 0; i < pFeatures.Count; i++)
{
MessageBox.Show(((pFeatures.Shape as IPolygon) as IArea).Area.ToString());
}
分析：pFeatures集合存儲(chǔ)了指向FeatureClass上所有Feature的引用，但是由于Recycling參數(shù)設(shè)置為TRUE也就是說沒執(zhí)行一個(gè)NextFeautre方法上一條記錄的Feature值在內(nèi)存中被回收，所以到最后遍歷pFeatures集合的時(shí)候所有的IFeature引用指向的Feature對(duì)象都為Null。所以會(huì)引發(fā)一下錯(cuò)誤（如下圖所示）：
2.參數(shù)Recycling設(shè)置為False
IFeatureClass pFeatureClass = (this.axMapControl1.get_Layer(0) as IFeatureLayer).FeatureClass;
//IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, true);
IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, false);
List<IFeature> pFeatures = new List<IFeature>();
IFeature pFeature = pFeatureCursor.NextFeature();
while (pFeature != null)
{
pFeatures.Add(pFeature);
pFeature = pFeatureCursor.NextFeature();
}
for (int i = 0; i < pFeatures.Count; i++)
{
MessageBox.Show(((pFeatures.Shape as IPolygon) as IArea).Area.ToString());
}
分析：pFeatures集合存儲(chǔ)了指向FeatureClass上所有Feature的引用，但是由于Recycling參數(shù)設(shè)置為False也就是說每執(zhí)行一個(gè)NextFeautre方法上一條記錄的Feature值在內(nèi)存中依然存在，所以到最后遍歷pFeatures集合的時(shí)候所有的 IFeature引用指向的Feature對(duì)象都依然存在。所以會(huì)執(zhí)行的很Happy（如下圖所示）：
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