本文通過一個簡單的小Demo，向大家介紹如何使用ArcGIS Android API繪製點、線、面圖形，並且測量線的長度和多邊形的面積。

首先來看一下程式執行的效果圖：

實現上述功能，首先需要向地圖中新增一個GraphicsLayer，用來繪製Point、Polyline、Polygon等Graphic物件。其次需要監聽地圖的Touch事件，即繼承MapOnTouchListener類。最後呼叫Line或Polyline物件的calculateLength2D方法計算長度，呼叫Polygon物件的calculateArea2D的方法計算面積。

主要程式碼如下：

	<com.esri.android.map.MapView
	    android:id="@+id/map"
	    android:layout_width="fill_parent"
	    android:layout_height="fill_parent"   
	    initExtent = "11575115, 3575676, 11596612, 3599415" 
	/>
 

	private MapView map;
	private GraphicsLayer drawLayer;
	private String strMapUrl="http://www.arcgisonline.cn/ArcGIS/rest/services/ChinaCities_Community_BaseMap_CHN/ChengDu_Community_BaseMap_CHN/MapServer";
	private SimpleLineSymbol lineSymbol;
	private SimpleMarkerSymbol markerSymbol;
	private SimpleFillSymbol fillSymbol;
	private MapTouchListener mapTouchListener;
在MeasureTestActivity類的onCreate方法中獲取地圖，新增圖層：
		map = (MapView)findViewById(R.id.map);
		ArcGISTiledMapServiceLayer baseMapLayer = new ArcGISTiledMapServiceLayer(strMapUrl);
		map.addLayer(baseMapLayer);
		
		drawLayer = new GraphicsLayer();
		map.addLayer(drawLayer);
還是在MeasureTestActivity類的onCreate方法中，新增對地圖touch事件的監聽：
		mapTouchListener = new MapTouchListener(MeasureTestActivity.this, map);
		map.setOnTouchListener(mapTouchListener);
 

    class MapTouchListener extends MapOnTouchListener {
    	private Geometry.Type geoType = null;//用於判定當前選擇的幾何圖形型別
    	private Point ptStart = null;//起點
    	private Point ptPrevious = null;//上一個點
    	private ArrayList<Point> points = null;//記錄全部點
    	private Polygon tempPolygon = null;//記錄繪製過程中的多邊形
    	
		public MapTouchListener(Context context, MapView view) {
			super(context, view);
			
			points = new ArrayList<Point>();
		}
		
		// 根據使用者選擇設定當前繪製的幾何圖形型別
		public void setType(String geometryType) {
			if(geometryType.equalsIgnoreCase("Point"))
				this.geoType = Geometry.Type.Point;
			else if(geometryType.equalsIgnoreCase("Polyline"))
				this.geoType = Geometry.Type.Polyline;
			else if(geometryType.equalsIgnoreCase("Polygon"))
				this.geoType = Geometry.Type.Polygon;
		}
		
		public Geometry.Type getType() {
			return this.geoType;
		}

		@Override
		public boolean onSingleTap(MotionEvent point) {
			Point ptCurrent = map.toMapPoint(new Point(point.getX(), point.getY()));
			if(ptStart == null) drawLayer.removeAll();//第一次開始前，清空全部graphic
			
			if (geoType == Geometry.Type.Point) {//直接畫點				
				drawLayer.removeAll();
				ptStart = ptCurrent;

				Graphic graphic = new Graphic(ptStart,markerSymbol);
				drawLayer.addGraphic(graphic);
				
				btnClear.setEnabled(true);
				return true;
			}
			else//繪製線或多邊形
			{
				points.add(ptCurrent);//將當前點加入點集合中
				
				if(ptStart == null){//畫線或多邊形的第一個點
					ptStart = ptCurrent;
										
					//繪製第一個點
					Graphic graphic = new Graphic(ptStart,markerSymbol);
					drawLayer.addGraphic(graphic);									
				}
				else{//畫線或多邊形的其他點
					//繪製其他點
					Graphic graphic = new Graphic(ptCurrent,markerSymbol);
					drawLayer.addGraphic(graphic);
					
					//生成當前線段（由當前點和上一個點構成）
					Line line = new Line();
					line.setStart(ptPrevious);
					line.setEnd(ptCurrent);
					
					if(geoType == Geometry.Type.Polyline){
						//繪製當前線段
						Polyline polyline = new Polyline();
						polyline.addSegment(line, true);
						
						Graphic g = new Graphic(polyline, lineSymbol);
						drawLayer.addGraphic(g);
						
						// 計算當前線段的長度
						String length = Double.toString(Math.round(line.calculateLength2D())) + " 米";
						
						Toast.makeText(map.getContext(), length, Toast.LENGTH_SHORT).show();
					}
					else{
						//繪製臨時多邊形
						if(tempPolygon == null) tempPolygon = new Polygon();
						tempPolygon.addSegment(line, false);
						
						drawLayer.removeAll();
						Graphic g = new Graphic(tempPolygon, fillSymbol);
						drawLayer.addGraphic(g);
						
						//計算當前面積
						String sArea = getAreaString(tempPolygon.calculateArea2D());
						
						Toast.makeText(map.getContext(), sArea, Toast.LENGTH_SHORT).show();
					}
				}
				
				ptPrevious = ptCurrent;
				return true;
			}
		}
		
		@Override
		public boolean onDoubleTap(MotionEvent point) {
			drawLayer.removeAll();
			if(bIsMeasureLength == true){
				Polyline polyline = new Polyline();
	
				Point startPoint = null;
				Point endPoint = null;
				
				// 繪製完整的線段
				for(int i=1;i<points.size();i++){
					startPoint = points.get(i-1);
					endPoint = points.get(i);
					
					Line line = new Line();
					line.setStart(startPoint);
					line.setEnd(endPoint);

					polyline.addSegment(line, false);
				}
				
				Graphic g = new Graphic(polyline, lineSymbol);
				drawLayer.addGraphic(g);
				
				// 計算總長度
				String length = Double.toString(Math.round(polyline.calculateLength2D())) + " 米";
				
				Toast.makeText(map.getContext(), length, Toast.LENGTH_SHORT).show();
			}
			else{
				Polygon polygon = new Polygon();

				Point startPoint = null;
				Point endPoint = null;
				// 繪製完整的多邊形
				for(int i=1;i<points.size();i++){
					startPoint = points.get(i-1);
					endPoint = points.get(i);
					
					Line line = new Line();
					line.setStart(startPoint);
					line.setEnd(endPoint);

					polygon.addSegment(line, false);
				}
				
				Graphic g = new Graphic(polygon, fillSymbol);
				drawLayer.addGraphic(g);
						
				// 計算總面積
				String sArea = getAreaString(polygon.calculateArea2D());
				
				Toast.makeText(map.getContext(), sArea, Toast.LENGTH_SHORT).show();
			}
			
			// 其他清理工作
			btnClear.setEnabled(true);
			ptStart = null;
			ptPrevious = null;
			points.clear();
			tempPolygon = null;
			
			return false;
		}	
		
		private String getAreaString(double dValue){
			long area = Math.abs(Math.round(dValue));
			String sArea = "";
			// 順時針繪製多邊形，面積為正，逆時針繪製，則面積為負
			if(area >= 1000000){					
				double dArea = area / 1000000.0;
				sArea = Double.toString(dArea) + " 平方公里";
			}
			else
				sArea = Double.toString(area) + " 平方米";
			
			return sArea;
		}
    }