FindPreviousElement Method

Summary

Returns the previous item in the Data Set with a specific Tag.

Syntax

Objective-C

C++/CLI

Java

public DicomElement FindPreviousElement( 
   DicomElement element, 
   bool tree 
)

- (nullable LTDicomElement *)findPreviousElement:(LTDicomElement *)element tree:(BOOL)tree;

public DicomElement findPreviousElement(DicomElement element, boolean tree)

public: 
DicomElement^ FindPreviousElement(  
   DicomElement^ element, 
   bool tree 
)

Parameters

element
An item in the Data Set.

tree
true to evaluate the Data Set as a tree; false to evaluate the Data Set as a list.

Return Value

The previous item in the Data Set with a specified Tag, or a null reference (Nothing in VB) if a previous item with the specified Tag was not found.

Remarks

Note: This method does not specify a Tag to use when searching. However the Tag that was used in the last call to FindFirstElement or FindLastElement is used by default when searching. For the sake of the following illustrations, the order of siblings is top to bottom.

If the Data Set is evaluated as a tree structure, this method returns the previous item on the same level as element, with the same parent as element.

Please note that the numbering of the items of interest in this first illustration is arbitrary and does not imply order.

If the passed object points to:	The method returns an object pointing to:
Item 1	The previous sibling (same level, same parent) of Item 1 , if such an item exists. If such an item does not exist, the method returns null.
Item 2	The previous sibling (same level, same parent) of Item 2 , if such an item exists. If such an item does not exist, the method returns null.
Item 3	The previous sibling (same level, same parent) of Item 3, if such an item exists. If such an item does not exist, the method returns null.

If the Data Set is evaluated as a list, this method returns the previous item in the entire list .

Please note that the numbering of the items in the following illustration does indicate the order of the items when the Data Set is evaluated as a list.

If the passed object points to:	The method returns an object pointing to:
Item 1	The previous item in the list, if such an item exists. If an item with Tag tag is not found, null is returned.
Item 14	The previous item in the list that has Tag tag, if such an item exists. If an item with Tag tag is not found, null is returned.
Item 22	The previous item in the list that has Tag tag, if such an item exists. If an item with Tag tag is not found, null is returned.

The following methods will also help you find elements in the Data Set with a specific Tag:

FindFirstElement

FindLastElement

FindNextElement

The following methods will help you find specific modules in the Data Set:

FindModule

FindModuleByIndex

Example

using Leadtools; 
using Leadtools.Dicom; 
 
 
public void LoadEnumerateSample() 
{ 
   string dicomFileName = Path.Combine(LEAD_VARS.ImagesDir, "DICOM", "image3.dcm"); 
   //Make sure to initialize the DICOM engine, this needs to be done only once  
   //In the whole application 
   DicomEngine.Startup(); 
   using (DicomDataSet ds = new DicomDataSet()) 
   { 
      //Load DICOM File 
      ds.Load(dicomFileName, DicomDataSetLoadFlags.None); 
      //Insert patient name element, if it doesn't already exist 
      DicomElement element = ds.FindFirstElement(null, DicomTag.PatientName, false); 
      if (element == null) 
      { 
         element = ds.InsertElement(null, false, DicomTag.PatientName, DicomVRType.PN, false, 0); 
      } 
      //The dataset should include the patient name element or an error occurred 
      element = ds.FindLastElement(null, DicomTag.PatientName, false); 
      Debug.Assert(element != null); 
      //There can be only one patient element in the root level 
      element = ds.FindPreviousElement(null, false); 
      Debug.Assert(element == null); 
      element = ds.FindNextElement(null, false); 
      Debug.Assert(element == null); 
 
      element = ds.FindFirstElement(null, DicomTag.PatientName, false); 
      //Since the patient name element is in the root level, 
      //GetRootElement will return the same element. 
      DicomElement element1 = ds.GetRootElement(element); 
      Debug.Assert((element1.Tag == element.Tag), "GetRootElement should return same element"); 
 
      //Since the patient name element has no parent then GetParentElement will return null 
      element1 = ds.GetParentElement(element); 
      Debug.Assert(element1 == null, "GetParentElement should return null"); 
 
      //Since the patient name element has no children then GetChildElement will return null 
      element1 = ds.GetChildElement(element, false); 
      Debug.Assert(element1 == null, "GetChildElement should return null"); 
 
      element1 = ds.GetFirstElement(element, false, false); 
      Debug.Assert(element1 != null, "GetFirstElement Can't return null in this case"); 
 
      element1 = ds.GetLastElement(element, false, false); 
      Debug.Assert(element1 != null, "GetLastElement Can't return null in this case"); 
 
      element1 = ds.GetPreviousElement(element, false, true); 
      DicomElement element2 = ds.GetNextElement(element, false, true); 
 
      Debug.Assert(ds.GetElementLevel(element) == 0); 
 
      Debug.Assert(ds.ExistsElement(element)); 
      Debug.Assert(ds.IsVolatileElement(element) == false); 
 
      //Patient Name is not the only element in this level 
      Debug.Assert((element1 != null) && (element2 != null)); 
      //Delete the patient name element 
      ds.DeleteElement(element); 
   } 
   DicomEngine.Shutdown(); 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\LEADTOOLS22\Resources\Images"; 
}