如何在Android上使用Spatialite和Xamarin

Question

我想在Android上使用Spatialite而不是简单的SQLite和Xamarin来管理和显示地理数据.内置的SQLite不允许加载扩展.我该怎么做？

Answer 1

简短回答:您需要使用自己定制的SQLite作为Android Native Library,就像使用其他NDK库一样.棘手的部分是为数据库提供有用而不是那么简单的C#API.Xamarin docs似乎只有非常简单的单一方法API的指南.

由于我比Java更熟悉Java,因此我使用了Android Java库(.jar)和Android本机库(.so)的组合.Android Java库已经为数据库提供了Java API包装器,它与通常的Android Java应用程序中使用的包装器完全相同.当然,技术上也可以从C#直接访问本机库,因此可以从故事中排除java/jar.如果你知道好的工具,请告诉我.

1. 为Xamarin创建.jar绑定项目,将其添加到与Android项目相同的解决方案中
2. 将jsqlite.jar添加到绑定项目的Jars文件夹中.从这里获取它:jsqlite.jar
3. 将本机库二进制文件(libjsqlite.so和libproj.so)添加到您的应用程序项目中,为此创建文件夹libs/armeabi.从Nutiteq AdvancedMap3D项目中获取这些内容
4. 将.so文件定义为AndroidNativeLibrary,并将Copy设置为Output Directory
5. 修复绑定定义以删除生成错误.将以下内容添加到绑定项目的Transforms/Metadata.xml:

<remove-node path="/api/package[@name='jsqlite']/class[@name='Backup']/field[@name='handle']" />
<remove-node path="/api/package[@name='jsqlite']/class[@name='Database']/field[@name='handle']"/>
<attr path="/api/package[@name='jsqlite']" name="managedName">jsqlite</attr>

这应该会为捆绑的SQLite生成C#API,包括Spatialite,Proj.4和GEOS.jsqlite DB API本身与其他C#SQLite API不同,您需要使用回调类.请参阅以下示例要检查模块的版本:

try {
  db.Open ("/sdcard/mapxt/estonia-latest-map.sqlite", Constants.SqliteOpenReadonly);
  // show versions to verify that modules are there
  db.Exec ("SELECT spatialite_version(), proj4_version(), geos_version(), sqlite_version()", new GeneralQryResult ());
} catch (jsqlite.Exception ex) {
  Log.Error( ex.LocalizedMessage );
}

...

// prints query results as text
public class GeneralQryResult : Java.Lang.Object, ICallback
{

    public bool Newrow (string[] rowdata)
    {
        string row = "";
        foreach (var data in rowdata) {
            row += data + " | ";
        }

        Log.Info(row);
        return false;
    }

    public void Types (string[] types)
    {
        // never called really
    }

    public void Columns (string[] cols){
        Log.Debug ("Query result:");
        string row = "";
        foreach (var col in cols) {
            row += col + " | ";
        }
        Log.Info (row);
    }
}

最后,现在查询真实的空间数据,使用Nutiteq 3D Maps SDK for Xamarin进行可视化:

// Spatialite query, show results on map
// 1. create style and layer for data

LineStyle.Builder lineStyleBuilder = new LineStyle.Builder ();
lineStyleBuilder.SetColor (NutiteqComponents.Color.Argb(0xff, 0x5C, 0x40, 0x33)); //brown
lineStyleBuilder.SetWidth (0.05f);
LineStyle lineStyle = lineStyleBuilder.Build ();

GeometryLayer geomLayer = new GeometryLayer (view.Layers.BaseLayer.Projection);
view.Layers.AddLayer (geomLayer);

// 2. do the query, pass results to the layer
Database db = new Database ();

try {
    db.Open ("/sdcard/mapxt/estonia-latest-map.sqlite", Constants.SqliteOpenReadonly);

    // spatial query. Limit to 1000 objects to avoid layer overloading
    String qry = "SELECT id, HEX(AsBinary(Transform(geometry,3857))), sub_type, name FROM ln_railway LIMIT 1000";
    db.Exec (qry, new SpatialQryResult (geomLayer, lineStyle));
} catch (jsqlite.Exception ex) {
    Log.Error( ex.LocalizedMessage );
}

...

// adds query results to given layer, with given style
public class SpatialQryResult : Java.Lang.Object, ICallback
{

    GeometryLayer _geomLayer;
    Style _geomStyle;

    public SpatialQryResult(GeometryLayer geomLayer, Style geomStyle){
        _geomLayer = geomLayer;
        _geomStyle = geomStyle;
    }

    public bool Newrow (string[] rowdata)
    {

        string id = rowdata [0];
        string geomHex = rowdata [1];
        string type = rowdata [2];
        string name = rowdata [3];

        Label label;
        if (name != null && name.Length > 1) {
            label = new DefaultLabel (name, type);
        } else {
            label = null;
        }

        Geometry[] lineGeoms = WkbRead.ReadWkb(new ByteArrayInputStream(Utils
            .HexStringToByteArray(geomHex)), rowdata);

        // following fails if not Line, change for other geometries
        foreach (Line lineGeom in lineGeoms) {
            _geomLayer.Add(new Line(lineGeom.VertexList, label, (LineStyle)_geomStyle, _geomLayer));
        }

        return false;
    }
}