12. 設定の読み込みと保存

ヒント

The code snippets on this page need the following imports if you're outside the pyqgis console:

1from qgis.core import (
2  QgsProject,
3  QgsSettings,
4  QgsVectorLayer
5)

多くの場合、プラグインでいくつかの変数が保存されて、そのプラグインを次に実行したときにユーザーがそれらの変数を入力したり選択したりする必要がないようにすると便利です。

これらの変数は保存され、QtとQGIS APIの助けを借りて取得できます。各変数について、変数にアクセスするために使用されるキーを選択する必要があります---ユーザの好みの色のためにキー「favourite_color」またはその他の意味のある文字列を使用できます。キーの名前をつけるときは何らかの構造を持たせることをお勧めします。

We can differentiate between several types of settings:

  • global settings --- they are bound to the user at a particular machine. QGIS itself stores a lot of global settings, for example, main window size or default snapping tolerance. Settings are handled using the QgsSettings class, through for example the setValue() and value() methods.

    Here you can see an example of how these methods are used.

     1def store():
 2  s = QgsSettings()
 3  s.setValue("myplugin/mytext", "hello world")
 4  s.setValue("myplugin/myint",  10)
 5  s.setValue("myplugin/myreal", 3.14)
 6
 7def read():
 8  s = QgsSettings()
 9  mytext = s.value("myplugin/mytext", "default text")
10  myint  = s.value("myplugin/myint", 123)
11  myreal = s.value("myplugin/myreal", 2.71)
12  nonexistent = s.value("myplugin/nonexistent", None)
13  print(mytext)
14  print(myint)
15  print(myreal)
16  print(nonexistent)

    The second parameter of the value() method is optional and specifies the default value that is returned if there is no previous value set for the passed setting name.

    For a method to pre-configure the default values of the global settings through the global_settings.ini file, see 組織内でのQGISの導入 for further details.

  • project settings --- vary between different projects and therefore they are connected with a project file. Map canvas background color or destination coordinate reference system (CRS) are examples --- white background and WGS84 might be suitable for one project, while yellow background and UTM projection are better for another one.

    An example of usage follows.

     1proj = QgsProject.instance()
 2
 3# store values
 4proj.writeEntry("myplugin", "mytext", "hello world")
 5proj.writeEntry("myplugin", "myint", 10)
 6proj.writeEntryDouble("myplugin", "mydouble", 0.01)
 7proj.writeEntryBool("myplugin", "mybool", True)
 8
 9# read values (returns a tuple with the value, and a status boolean
10# which communicates whether the value retrieved could be converted to
11# its type, in these cases a string, an integer, a double and a boolean
12# respectively)
13
14mytext, type_conversion_ok = proj.readEntry("myplugin",
15                                            "mytext",
16                                            "default text")
17myint, type_conversion_ok = proj.readNumEntry("myplugin",
18                                              "myint",
19                                              123)
20mydouble, type_conversion_ok = proj.readDoubleEntry("myplugin",
21                                                    "mydouble",
22                                                    123)
23mybool, type_conversion_ok = proj.readBoolEntry("myplugin",
24                                                "mybool",
25                                                123)

    As you can see, the writeEntry() method is used for many data types (integer, string, list), but several methods exist for reading the setting value back, and the corresponding one has to be selected for each data type.

  • map layer settings --- these settings are related to a particular instance of a map layer with a project. They are not connected with underlying data source of a layer, so if you create two map layer instances of one shapefile, they will not share the settings. The settings are stored inside the project file, so if the user opens the project again, the layer-related settings will be there again. The value for a given setting is retrieved using the customProperty() method, and can be set using the setCustomProperty() one.

    1vlayer = QgsVectorLayer()
2# save a value
3vlayer.setCustomProperty("mytext", "hello world")
4
5# read the value again (returning "default text" if not found)
6mytext = vlayer.customProperty("mytext", "default text")