GetPreviousKey Method

Summary

Returns the item in the Dicom Dir Data Set that immediately precedes the specified item.

Syntax

C++/CLI

Java

public DicomElement GetPreviousKey( 
   DicomElement element, 
   bool tree 
)

public DicomElement getPreviousKey(DicomElement element, boolean tree)

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

Parameters

element
An item in the Data Set. The item in the Data Set that immediately precedes this item will be returned.

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

Return Value

The item in the Data Set that immediately precedes the item specified by element, or a null reference (Nothing in VB) if there is no item preceding element (element is the first item in the Data Set).

Remarks

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 in the following illustration is arbitrary and does not imply order.

If the passed object points to:	The method returns an object pointing to:
Item 1	Item 2
Item 3	Item 4
Item 5	null
Item 6	Item 7

If the Data Set is evaluated as a list, the previous item in the list is returned. 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	null
Item 15	Item 14
Item 5	Item 4
Item 9	Item 8
Item 22	Item 21
Item 25	Item 24

The following methods will also help you navigate the Data Set as either a tree or a list:

GetFirstKey

GetNextKey

GetLastKey

If you evaluate the Data Set as a tree, you can also use the following methods to navigate the tree:

GetRootKey

GetParentKey

GetChildKey

Example

using Leadtools; 
using Leadtools.Dicom; 
 
 
public void DicomDIRSample() 
{ 
   //Make sure to initialize the DICOM engine, this needs to be done only once  
   DicomEngine.Startup(); 
   using (DicomDataSet dicomDIR = new DicomDataSet()) 
   { 
      dicomDIR.Reset(); 
      //Initialize the dataset as a DICOMDIR class 
      dicomDIR.Initialize(DicomClassType.BasicDirectory, DicomDataSetInitializeType.ExplicitVRLittleEndian); 
      Debug.Assert(dicomDIR.InformationClass == DicomClassType.BasicDirectory); 
      Debug.Assert(dicomDIR.InformationFlags == (DicomDataSetFlags.ExplicitVR | DicomDataSetFlags.LittleEndian | DicomDataSetFlags.MetaHeaderPresent)); 
      //Insert a patient level key 
      DicomElement patientKey = dicomDIR.InsertKey(null, DicomDirKeyType.Patient, true); 
      //Insert a study key under the patient key 
      DicomElement studyKey = dicomDIR.InsertKey(patientKey, DicomDirKeyType.Study, true); 
      //Now insert three series keys under the study key 
      DicomElement seriesKey = dicomDIR.InsertKey(studyKey, DicomDirKeyType.Series, true); 
      seriesKey = dicomDIR.InsertKey(studyKey, DicomDirKeyType.Series, true); 
      seriesKey = dicomDIR.InsertKey(studyKey, DicomDirKeyType.Series, true); 
      DicomElement key = dicomDIR.GetRootKey(seriesKey); 
      //Get the key value, You can also call GetKeyValuePtr 
      DicomDirKeyType keyValue = dicomDIR.GetKeyValue(key); 
      //The root key for the series key should be patient 
      Debug.Assert(keyValue == DicomDirKeyType.Patient, "The root key for the series key should be patient in this case"); 
      //Get the parent key for the series, it should be study 
      key = dicomDIR.GetParentKey(seriesKey); 
      keyValue = dicomDIR.GetKeyValue(key); 
      Debug.Assert(keyValue == DicomDirKeyType.Study, "The parent key for the series key should be study in this case"); 
      //The child for the study key should be series 
      key = dicomDIR.GetChildKey(studyKey); 
      keyValue = dicomDIR.GetKeyValue(key); 
      Debug.Assert(keyValue == DicomDirKeyType.Series, "The child for the study key should be series"); 
      //The first key should be patient, if we traverse the DICOMDIR as a list 
      key = dicomDIR.GetFirstKey(studyKey, false); 
      keyValue = dicomDIR.GetKeyValue(key); 
      Debug.Assert(keyValue == DicomDirKeyType.Patient); 
      //The last key should be series, if we traverse the DICOMDIR as a list 
      key = dicomDIR.GetLastKey(studyKey, false); 
      keyValue = dicomDIR.GetKeyValue(key); 
      Debug.Assert(keyValue == DicomDirKeyType.Series); 
      //The key before the study key should be patient, if we traverse the DICOMDIR as a list 
      key = dicomDIR.GetPreviousKey(studyKey, false); 
      keyValue = dicomDIR.GetKeyValue(key); 
      Debug.Assert(keyValue == DicomDirKeyType.Patient); 
      //The key after the study key should be series, if we traverse the DICOMDIR as a list 
      key = dicomDIR.GetNextKey(studyKey, false); 
      keyValue = dicomDIR.GetKeyValue(key); 
      Debug.Assert(keyValue == DicomDirKeyType.Series); 
      //If we delete the study key, the series keys under it will get deleted too 
      dicomDIR.DeleteKey(studyKey); 
      key = dicomDIR.FindFirstKey(null, DicomDirKeyType.Series, false); 
      Debug.Assert(key == null); 
      key = dicomDIR.FindLastKey(null, DicomDirKeyType.Series, false); 
      Debug.Assert(key == null); 
      key = dicomDIR.FindPreviousKey(null, false); 
      Debug.Assert(key == null); 
      key = dicomDIR.FindNextKey(null, false); 
      Debug.Assert(key == null); 
   } 
   DicomEngine.Shutdown(); 
}