Samuel Bosch

Showing posts with label ArcObjects. Show all posts

Using yield to create an iterator

Not so long ago I blogged about using the foreach statement with an ICursor. I achieved this by inheriting from IEnumerator and IEnumerable.

But by using the yield statement we can achieve a similar effect with much less code. The generator function looks like this:

public static IEnumerable<IFeature> Iter(IFeatureCursor cursor)
{
    IFeature feat;
    while((feat = cursor.NextFeature()) != null)
    {
        yield return feat;
    }
    yield break;
}

You can use this method like below.

IFeatureClass featureClass; // initialize feature class
IQueryFilter queryFilter = new QueryFilterClass();
queryFilter.WhereClause = ... your where clause here ...
bool recycling = true;
IEnumerable<IFeature> features = Iter(featureClass.Search(queryFilter, recycling));
foreach (IFeature feature in features)
{
    ... your code here ...
}

If you're running .NET 3.0 or more you can create the following extension method in an extension class. This method adds the SearchIter method to the IFeatureClass interface which replaces the Search method.

public static class Extensions
{
    public static IEnumerable<IFeature> SearchIter(this IFeatureClass featureClass, IQueryFilter queryFilter, bool recycling)
    {
        IFeatureCursor cursor = featureClass.Search(queryFilter, recycling);
        IFeature feat;
        while ((feat = cursor.NextFeature()) != null)
        {
            yield return feat;
        }
        yield break;
    }
}

The usage of the extension method is similar to the usage of the Iter method but you can replace

IEnumerable<IFeature> features = Iter(featureClass.Search(queryFilter, recycling));

with this

IEnumerable<IFeature> features = featureClass.SearchIter(queryFilter, recycling);

So this was it. I hope you learned something and feel free to leave a comment.

Editing with ArcObjects

Recently I found myself rewriting a lot of code which started and stopped edit sessions to decorate it with try ... finally blocks to make sure that every started edit session closes even when an error occurs. The code I wrote looked like below.

bool saveEdits = false;
try
{
    StartEditing();
    ... edit a featureclass or table ...
    saveEdits = true;
}
finally
{
    StopEditing(saveEdits);
}

I thought that there had to be a cleaner way to achieve the same functionality. Here comes the using statement to the rescue. To be able to use the using statement with a class it has to implement the IDisposable interface. So I wrote the following wrapper class for starting and stopping edit sessions.

public class EditSession : IDisposable
{
    IWorkspaceEdit _workspaceEdit = null;

    public IWorkspaceEdit WorkspaceEdit
    {
        get { return _workspaceEdit; }
        set { _workspaceEdit = value; }
    }

    public EditSession(IWorkspace workspace, bool withUndoRedo)
    {
        if (workspace != null)
        {
            _workspaceEdit = (IWorkspaceEdit)workspace;
        }
    }

    public static EditSession Start(IWorkspace workspace, bool withUndoRedo)
    {
        EditSession editSession = new EditSession(workspace, withUndoRedo);
        editSession.Start(withUndoRedo);
        return editSession;
    }

    public void Start(bool withUndoRedo)
    {
        if (_workspaceEdit.IsBeingEdited() == false)
        {
            _workspaceEdit.StartEditing(withUndoRedo);
            _workspaceEdit.StartEditOperation();
        }
    }

    public void SaveAndStop()
    {
        Stop(true);
    }

    public void Stop(bool save)
    {
        if (_workspaceEdit.IsBeingEdited() == true)
        {
            _workspaceEdit.StopEditOperation();
            _workspaceEdit.StopEditing(save);
        }
    }

    #region IDisposable Members

    public void Dispose()
    {
        if (_workspaceEdit != null && _workspaceEdit.IsBeingEdited())
        {
            Stop(false);
        }
    }

    #endregion
}

You can use the EditSession class like this.

using (EditSession editSession = EditSession.Start(workspace, false))
{
    ... edit a featureclass or table ...
    editSession.SaveAndStop();
}

If you're using .NET 3.0 or a later version you can use the following class which creates an extension method for the IWorkspace.

public static class Extensions
{
    public static EditSession StartEditing(this IWorkspace workspace, bool withUndoRedo)
    {
        return EditSession.Start(workspace, withUndoRedo);
    }
}

With the extension method you can directly call StartEditing on a workspace.

using (EditSession editSession = workspace.StartEditing(false))
{
    ... edit a featureclass or table ...
    editSession.SaveAndStop();
}

Inserting Features and Rows

Recently I was inserting features in a feature class but my code was rather slow so I looked around for another method and the following is what I found.

First you need to start an edit session and then you can use the code below. This is just a short body of code to give you an idea on how to use the different objects.

IFeatureCursor insertFeatCursor = outputFeatClass.Insert(true);

foreach (object featureToInsert in featuresToInsert)
{
    IFeatureBuffer outputFeatBuffer = outputFeatClass.CreateFeatureBuffer();
    // set the shape
    outputFeatBuffer.Shape = ...
    // set the different values
    outputFeatBuffer.set_Value(fieldIndex, value);
    // insert the feature buffer
    insertFeatCursor.InsertFeature(outputFeatBuffer);
}
insertFeatCursor.Flush();

If you now save and close your edit session the features are inserted. The code for inserting rows in a table is very similar.

ITable table;
ICursor insertCursor = table.Insert(true);
IRowBuffer rowBuffer = table.CreateRowBuffer();
rowBuffer.set_Value(fieldIndex, value);
insertCursor.InsertRow(rowBuffer);
insertCursor.Flush();

If you have any comments or questions, let me know !!!

Using foreach with the ICursor

My first post on this blog was about how to loop over an ESRI cursor in Python with the for statement instead of the while statement. The same problem exists in .NET when using the various cursor objects like ICursor and IFeatureCursor. Normally you would code something like this :

ICursor cursor = table.Search(null, false);
IRow row;
while ((row = cursor.NextRow()) != null)
{
    // some code
}

Or this:

ICursor cursor = table.Search(null, false);
IRow row = cursor.NextRow();
while (row != null)
{
    // some code
    row = cursor.NextRow();
}

And I want to replace it with the following.

ITable table; // get table from somewhere
IQueryFilter queryFilter; // create QueryFilter or leave it null
CursorGS cursorGS = new CursorGS(table, queryFilter);
foreach (IRow row in cursorGS)
{
    // ... insert your code here
}

To make a class usable in a foreach statement you need to implement the IEnumerable and IEnumerator interfaces. I found a good introduction to making class usable in a foreach statement in this Microsoft article. So what I did was creating a class that inherited from IEnumerator<IRow> and IEnumerable<IRow> and implement all the needed properties and methods. For IEnumerator these where Current, MoveNext, Reset and Dispose and for IEnumerable only the method GetEnumerator was needed. The biggest problem was the Reset method because an ICursor doesn't have a reset method. I decided to set the cursor null and the recreated at the moment that MoveNext is called. This also makes sure the ICursor is only created when we really need it. Below you can find my full class

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using ESRI.ArcGIS.Geodatabase;

namespace GisSolved.GeoDiff.Esri
{
    public class CursorGS : IEnumerator<IRow>, IEnumerable<IRow>
    {
        ITable _table;
        IQueryFilter _queryFilter;

        ESRI.ArcGIS.ADF.ComReleaser _comReleaser;
        IRow _currentRow = null;
        ICursor _cursor = null;

        public CursorGS(ITable table, IQueryFilter queryFilter)
        {
            _table = table;
            _queryFilter = queryFilter;
            _comReleaser = new ESRI.ArcGIS.ADF.ComReleaser();
        }

        #region IEnumerator<IRow> Members

        public IRow Current
        {
            get { return _currentRow; }
        }

        #endregion

        #region IEnumerator Members

        object System.Collections.IEnumerator.Current
        {
            get { return _currentRow; }
        }

        public bool MoveNext()
        {
            if(_cursor == null) // initialize the cursor
            {
                _cursor = _table.Search(_queryFilter, false);
                _comReleaser.ManageLifetime(_cursor);
            }
            _currentRow = _cursor.NextRow();
            return _currentRow != null;
        }

        public void Reset()
        {
            _cursor = null;
        }

        #endregion

        #region IEnumerable<IRow> Members

        public IEnumerator<IRow> GetEnumerator()
        {
            return (IEnumerator<IRow>)this;
        }

        #endregion

        #region IEnumerable Members

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return (System.Collections.IEnumerator)this;
        }

        #endregion

        #region IDisposable Members

        public void Dispose()
        {
            _comReleaser.Dispose();
        }

        #endregion
    }
}

As you can see I used the ESRI ComReleaser object to make sure that the ICursor references get released properly.

So now you know how to create a wrapper around the ICursor you can start creating other wrappers for often used cursors like the IFeatureCursor, IFields, ... and I can go to my bed. Success and feel free to post any comments or your implementation !!!

Drag Drop from ArcCatalog

As you probably already noticed you can drag drop items within ArcGIS. For example you can drag a feature class from ArcCatalog to ArcMap or from ArcMap or ArcCatalog to a geoprocessing form. In this post I'm going to show you what has to be done to enable drag drop behavior from ArcCatalog and Windows Explorer to a textbox.

To enable drag drop on a textbox I added event handlers for DragEnter, DragOver and DragDrop for my textbox called textBoxPath. In the DragEnter and DragOver handlers I check whether the dragged object is valid. If this is the case the drag drop effect is set to All. This is a combination of the Copy, Move, and Scroll effect. But its in the DragDrop event handler and more precisely in the helper function GetPaths that the most import stuff happens. As you can see the Data property of the DragEventArgs is processed by the GetPaths method and if any paths to feature classes or tables are found the first path is shown. After that I added a small hack to put the cursor at the end of the text in the textbox.

private void TextBoxPath_DragEnter(object sender, DragEventArgs e)
{
 e.Effect = EsriDragDrop.IsValid(e.Data) ? DragDropEffects.All : DragDropEffects.None;
}

private void TextBoxPath_DragOver(object sender, DragEventArgs e)
{
 e.Effect = EsriDragDrop.IsValid(e.Data) ? DragDropEffects.All : DragDropEffects.None;
}

private void TextBoxPath_DragDrop(object sender, DragEventArgs e)
{
 List<string> paths = EsriDragDrop.GetPaths(e.Data);
 TextBox txtBoxPath = (TextBox)sender;
 if (paths.Count > 0)
 {
  // set value of textbox to the first found path
  txtBoxPath.Text = esriDragDrop.Paths[0];
  // place cursor at the end of the textbox
  txtBoxPath.SelectionStart = txtBoxPath.TextLength;
 }
}

In the below EsriDragDrop class I placed the IsValid and GetPaths methods. The IsValid method checks whether the IDataObject coming from the drag event contains any valid objects. The GetPaths method retrieves those valid objects and returns the paths to the found feature classes and tables. It uses the IDataObjectHelper interface and its GetNames and GetFiles methods to access the objects in the IDataObject. Note that only feature classes and tables will be returned by my code but this constraint can easily be removed by not checking the Type of the datasetName. I didn't add any functionality to check whether the file path dragged from a Windows Explorer to the textbox was valid but you can implement this by using the Geoprocessor object and its Exists and Describe methods or by trying to open the table or feature class.

using System.Collections.Generic;
using System.Windows.Forms;
using ESRI.ArcGIS.esriSystem;
using ESRI.ArcGIS.Geodatabase;
using ESRI.ArcGIS.SystemUI;

namespace GisSolved.DragDrop
{
 public class EsriDragDrop
 {
  const string DATAOBJECT_ESRINAMES = "ESRI Names";
  public static bool IsValid(IDataObject dataObject)
  {
   return dataObject.GetDataPresent(DATAOBJECT_ESRINAMES) ||
    dataObject.GetDataPresent(System.Windows.Forms.DataFormats.FileDrop);
  }
  public static List<string> GetPaths(IDataObject dataObject)
  {
   List<string> foundPaths = new List<string>();
   IDataObjectHelper dataObjectHelper = new DataObjectHelperClass();
   dataObjectHelper.InternalObject = (object)dataObject;
   
   if (dataObjectHelper.CanGetNames())
   {
    IEnumName enumNames = dataObjectHelper.GetNames();
    IName name;
    while ((name = enumNames.Next()) != null)
    {
     if (name is IDatasetName)
     {
      IDatasetName datasetName = (IDatasetName)name;
      // only accept feature classes and tables
      if (datasetName.Type == esriDatasetType.esriDTFeatureClass ||
       datasetName.Type == esriDatasetType.esriDTTable)
      {
       string path = System.IO.Path.Combine(datasetName.WorkspaceName.PathName, datasetName.Name);
       foundPaths.Add(path);
      }
     }
    }
   }
   else if (dataObjectHelper.CanGetFiles())
   {
    string[] paths = (string[])dataObjectHelper.GetFiles();
    foreach (string path in paths)
    {
     // TODO : Add code here to check if the file path is a valid path
     foundPaths.Add(path);
    }
   }
   return foundPaths;
  }
 }
}

This is all you need to implement drag drop behavior from ArcCatalog or Windows Explorer to your textbox. If you want to implement drag drop from ArcMap to your form I suggest you to read this and this. Any comments or suggestions ? Let me know.

Pages

Using yield to create an iterator

Editing with ArcObjects

Inserting Features and Rows

Using foreach with the ICursor

Drag Drop from ArcCatalog