Difference between revisions of "Projects/Marble/ModelView"

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== Model and Data Location ==
 
== Model and Data Location ==
  
* At the moment, each Model contains the list/vector/tree of data it presents. This is not a problem per se, unless all those models present the same data, and retain their own copies. Once the time to edit this data comes, it is tedious or quite impossible to trace back all those copies.
+
* At the moment, each Model contains the list/vector/tree of data it presents. This is not a problem per se, unless all those models present the same data, and retain their own copies. We should ensure that we do not make copies of data throughout models, but use pointers to the same data instead.
  
 
The solution to this is twofold:  
 
The solution to this is twofold:  
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=== QAbstractItemModel ===
 
=== QAbstractItemModel ===
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* {{class|GeoDataTreeModel|kdeedu|4.x}}
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It represents the list of all {{class|GeoDataDocument|kdeedu|4.x}} registered through the {{class|FileManager|kdeedu|4.x}}.
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It has signals/slots to react to files being added or removed in the FileManager.
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It is used by the {{class|GeometryLayer|kdeedu|4.x}} which renders all {{class|GeoDataGeometry|kdeedu|4.x}} related placemarks.
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* {{class|GeoDataDebugModel|kdeedu|4.x}}
 
* {{class|GeoDataDebugModel|kdeedu|4.x}}
 
It represents a data file, parsed into a {{class|GeoDataDocument|kdeedu|4.x}} tree structure.
 
It represents a data file, parsed into a {{class|GeoDataDocument|kdeedu|4.x}} tree structure.
  
 
It is used by the {{class|DataViewPlugin|kdeedu|4.x}} debug plugin (and is broken atm)
 
It is used by the {{class|DataViewPlugin|kdeedu|4.x}} debug plugin (and is broken atm)
 
* {{class|GpxFileModel|kdeedu|4.x}}
 
It represents a list of gpx data file represented as {{class|GpxFile|kdeedu|4.x}}
 
 
This was originally intended to but used as the model for the File List View ( which is accessible by running marble with --enableFileView ) but has since been replaced by the FileViewModel.
 
 
The model that is in the GpsLayer is currently only being used as a collection class and is deprecated. This, along with the whole current GPX implementation, needs to be removed and updated to the current concepts in Marble. See [[Projects/Marble/GPXStatus|Gpx Status]]
 
 
* {{class|MarbleGeometryModel|kdeedu|4.x}}
 
It represents the {{class|GeoDataGeometry|kdeedu}} and the {{class|GeoDataFeature|kdeedu|4.x}} items of the last opened {{class|GeoDataDocument|kdeedu|4.x}}.
 
 
It is used by the {{class|GeoRenderPlugin|kdeedu|4.x}} to access the list of vector data to draw it.
 
 
Action is underway to replace this class with a more generic model, which would hold all opened documents.
 
  
 
=== QAbstractListModel ===
 
=== QAbstractListModel ===
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It is used by the {{class|FileViewFloatItem|kdeedu|4.x}} and manipulated by the {{class|FileManager|kdeedu|4.x}}.
 
It is used by the {{class|FileViewFloatItem|kdeedu|4.x}} and manipulated by the {{class|FileManager|kdeedu|4.x}}.
 
* {{class|MarbleGeoDataModel|kdeedu|4.x}}
 
It represents a list of {{class|GeoDataDocuments|kdeedu|4.x}}. Only the {{class|PlacemarksPlugin|kdeedu|4.x}} uses it
 
 
It is used by no other code. It should be removed.
 
  
 
* {{class|MarblePlacemarkModel|kdeedu|4.x}}
 
* {{class|MarblePlacemarkModel|kdeedu|4.x}}

Revision as of 00:55, 15 August 2010

Contents

ModelView framework in Marble

Marble uses Qt's Model/View framework as a way to signal updates to a model to interested parts. In that respect, a Model class can wrap any possible data.

The multiple models in Marble each fit the purpose of feeding some GeoData classes to interested widgets. The way those models are fed could be improved however:

Model and Data Location

  • At the moment, each Model contains the list/vector/tree of data it presents. This is not a problem per se, unless all those models present the same data, and retain their own copies. We should ensure that we do not make copies of data throughout models, but use pointers to the same data instead.

The solution to this is twofold:

    • keep data unique in one store (wherever that is, a Model class or a list in one Manager)
    • Try and manipulate references to the data in the Models in such a case: with one change to the central data, multiple models can be notified and each react differently for the views they feed.

Model or not Model

  • The Model-View framework is designed to hide the details of the model content, and to present it in a standardised way to views. The advantage of this solution is that the View need not know much about the data it presents.

This solution however is not a one size fit all, because an interested class with some knowledge of the GeoDataTypes for example would be far better off manipulating the methods of GeoData classes.

As a consequence, a choice should be made whether to access GeoData through the model-view framework (nice for a List Widget or for a generic presentation of 'data as a tree', really not so nice for a class which for example would like to calculate the bounding box of all geometric data of a GeoDataDocument, or even for the File read/write, as the knowledge of data types is really known).

State of the Model

There are multiple models with various levels of implementation. Some are needed, others should die...

Here is the list of Model class, and a description of how they are used.

QAbstractItemModel

It represents the list of all GeoDataDocument registered through the FileManager.

It has signals/slots to react to files being added or removed in the FileManager.

It is used by the GeometryLayer which renders all GeoDataGeometry related placemarks.

It represents a data file, parsed into a GeoDataDocument tree structure.

It is used by the DataViewPlugin debug plugin (and is broken atm)

QAbstractListModel

It represents the list of opened files. The FileManager appends the documents it opens.

It is used by the FileViewFloatItem and manipulated by the FileManager.

It represents the list of all Placemarks of all opened files. the PlaceMarkManager appends all the placemarks after reading a file.

It is used by the MarbleControlBox to provide the list of placemarks to search for, and by the PlacemarkLayout to determine layouting on the map.

It should be replaced by a more generic model, which would hold all open documents and provide both features and geometries. It could also be replaced with a ProxyModel around this new model.


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