Android简明开发教程十四：Context Menu 绘制几何图形

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上下文相关菜单（Context Menu）类同PC上按鼠标右键显示的菜单，在Android平台上是长按来激活Context Menu，Context Menu一般用来显示和当前UI内容相关的菜单。

Context Menu的用法和Option Menu非常类似：

首先是创建菜单资源，在res/menu 下新建menu_context_shape.xml，用来显示Oval，Pear，Shape2D:

<?xml version=”1.0″ encoding=”utf-8″?>
<menu
xmlns:android=”http://schemas.android.com/apk/res/android“>
<item
android:id=”@+id/mnuOval”
android:title=”Oval”>
</item>
<item
android:id=”@+id/mnuPear”
android:title=”Pear”>
</item>
<item
android:id=”@+id/mnuShape2DDemo”
android:title=”Shape2D”>
</item>
</menu>

展开Context Menu，是通过onCreateContextMenu 方法：

@Override

public void onCreateContextMenu(ContextMenu menu, View v, 

ContextMenuInfo menuInfo) { 

super.onCreateContextMenu(menu, v, menuInfo); 

MenuInflater inflater = getMenuInflater(); 

inflater.inflate(R.menu.menu_context_shape, menu); 
}

处理Context Menu事件：

@Override

public boolean onContextItemSelected(MenuItem item) { 

menuOption = item.getItemId(); 

drawImage(); 

return super.onContextItemSelected(item); 

}

为了在长按时能在View上显示Context Menu，需要为View注册Context Menu：

public void onCreate(Bundle savedInstanceState) { 

super.onCreate(savedInstanceState); 

registerForContextMenu(graphic2dView); 
}

完整代码如下：

public class Shape extends Graphics2DActivity { 

private int menuOption; 

public void onCreate(Bundle savedInstanceState) { 

super.onCreate(savedInstanceState); 

registerForContextMenu(graphic2dView); 

} 

@Override

protected void drawImage() { 

switch (menuOption) { 

case R.id.mnuOval: 

drawOval(); 

break; 

case R.id.mnuPear: 

drawPear(); 

break; 

case R.id.mnuShape2DDemo: 

drawShape2D(); 

break; 

default: 

drawOval(); 

break; 

} 

graphic2dView.refreshCanvas(); 

} 

@Override

public void onCreateContextMenu(ContextMenu menu, View v, 

ContextMenuInfo menuInfo) { 

super.onCreateContextMenu(menu, v, menuInfo); 

MenuInflater inflater = getMenuInflater(); 

inflater.inflate(R.menu.menu_context_shape, menu); 

} 

@Override

public boolean onContextItemSelected(MenuItem item) { 

menuOption = item.getItemId(); 

drawImage(); 

return super.onContextItemSelected(item); 

} 

private void drawOval() { 

AffineTransform mat1; 

/** Colors */

Color redColor = new Color(0x96ff0000, true); 

Color greenColor = new Color(0xff00ff00); 

mat1 = new AffineTransform(); 

mat1.translate(30, 40); 

mat1.rotate(-30 * Math.PI / 180.0); 

// Clear the canvas with white color. 

graphics2D.clear(Color.WHITE); 

graphics2D.Reset(); 

graphics2D.setAffineTransform(new AffineTransform()); 

SolidBrush brush = new SolidBrush(greenColor); 

graphics2D.fillOval(brush, 20, 60, 100, 50); 

com.mapdigit.drawing.Pen pen 

= new com.mapdigit.drawing.Pen(redColor, 5); 

graphics2D.setAffineTransform(mat1); 

graphics2D.drawOval(pen, 20, 60, 100, 50); 

} 

private void drawPear() { 

Ellipse circle, oval, leaf, stem; 

Area circ, ov, leaf1, leaf2, st1, st2; 

circle = new Ellipse(); 

oval = new Ellipse(); 

leaf = new Ellipse(); 

stem = new Ellipse(); 

circ = new Area(circle); 

ov = new Area(oval); 

leaf1 = new Area(leaf); 

leaf2 = new Area(leaf); 

st1 = new Area(stem); 

st2 = new Area(stem); 

graphics2D.clear(Color.WHITE); 

graphics2D.Reset(); 

int w = SharedGraphics2DInstance.CANVAS_WIDTH; 

int h = SharedGraphics2DInstance.CANVAS_HEIGHT; 

int ew = w / 2; 

int eh = h / 2; 

SolidBrush brush = new SolidBrush(Color.GREEN); 

graphics2D.setDefaultBrush(brush); 

// Creates the first leaf by filling the 

//intersection of two Area 

// objects created from an ellipse. 

leaf.setFrame(ew - 16, eh - 29, 15, 15); 

leaf1 = new Area(leaf); 

leaf.setFrame(ew - 14, eh - 47, 30, 30); 

leaf2 = new Area(leaf); 

leaf1.intersect(leaf2); 

graphics2D.fill(null, leaf1); 

// Creates the second leaf. 

leaf.setFrame(ew + 1, eh - 29, 15, 15); 

leaf1 = new Area(leaf); 

leaf2.intersect(leaf1); 

graphics2D.fill(null, leaf2); 

brush = new SolidBrush(Color.BLACK); 

graphics2D.setDefaultBrush(brush); 

// Creates the stem by filling the Area 

//resulting from the subtraction of two 

//Area objects created from an ellipse. 

stem.setFrame(ew, eh - 42, 40, 40); 

st1 = new Area(stem); 

stem.setFrame(ew + 3, eh - 47, 50, 50); 

st2 = new Area(stem); 

st1.subtract(st2); 

graphics2D.fill(null, st1); 

brush = new SolidBrush(Color.YELLOW); 

graphics2D.setDefaultBrush(brush); 

// Creates the pear itself by filling the 

//Area resulting from the union of two Area 

//objects created by two different ellipses. 

circle.setFrame(ew - 25, eh, 50, 50); 

oval.setFrame(ew - 19, eh - 20, 40, 70); 

circ = new Area(circle); 

ov = new Area(oval); 

circ.add(ov); 

graphics2D.fill(null, circ); 

} 

private void drawShape2D() { 

Color bg = Color.white; 

Color fg = Color.black; 

Color red = Color.red; 

Color white = Color.white; 

com.mapdigit.drawing.Pen pen 

= new com.mapdigit.drawing.Pen(fg, 1); 

SolidBrush brush = new SolidBrush(red); 

// Clear the canvas with white color. 

graphics2D.clear(bg); 

graphics2D.Reset(); 

Dimension d = new Dimension(SharedGraphics2DInstance.CANVAS_WIDTH, 

SharedGraphics2DInstance.CANVAS_HEIGHT); 

int gridWidth = d.width / 2; 

int gridHeight = d.height / 6; 

int x = 5; 

int y = 7; 

int rectWidth = gridWidth - 2 * x; 

int stringY = gridHeight - 3 - 2 - 16; 

int rectHeight = stringY - y - 2; 

graphics2D.draw(pen, new Line(x, y + rectHeight - 1, 

x + rectWidth, y)); 

x += gridWidth; 

graphics2D.draw(pen, new Rectangle(x, y, rectWidth, 

rectHeight)); 

x += gridWidth; 

x = 5; 

y += gridHeight; 

stringY += gridHeight; 

graphics2D.draw(pen, new RoundRectangle(x, y, rectWidth, 

rectHeight, 

10, 10)); 

x += gridWidth; 

graphics2D.draw(pen, new Arc(x, y, rectWidth, 

rectHeight, 90, 135, 

Arc.OPEN)); 

x = 5; 

y += gridHeight; 

stringY += gridHeight; 

graphics2D.draw(pen, new Ellipse(x, y, rectWidth, 

rectHeight)); 

x += gridWidth; 

// draw GeneralPath (polygon) 

int x1Points[] = { x, x + rectWidth, x, 

x + rectWidth }; 

int y1Points[] = { y, y + rectHeight, 

y + rectHeight, y }; 

com.mapdigit.drawing.geometry.Path polygon 

= new com.mapdigit.drawing.geometry.Path( 

com.mapdigit.drawing.geometry.Path.WIND_EVEN_ODD, 

x1Points.length); 

polygon.moveTo(x1Points[0], y1Points[0]); 

for (int index = 1; index < x1Points.length; index++) { 

polygon.lineTo(x1Points[index], y1Points[index]); 

} 

polygon.closePath(); 

graphics2D.draw(pen, polygon); 

x = 5; 

y += gridHeight; 

stringY += gridHeight; 

int x2Points[] = { x, x + rectWidth, x, x + rectWidth }; 

int y2Points[] = { y, y + rectHeight, y + rectHeight, y }; 

com.mapdigit.drawing.geometry.Path polyline 

= new com.mapdigit.drawing.geometry.Path( 

com.mapdigit.drawing.geometry.Path.WIND_EVEN_ODD, 

x2Points.length); 

polyline.moveTo(x2Points[0], y2Points[0]); 

for (int index = 1; index < x2Points.length; index++) { 

polyline.lineTo(x2Points[index], y2Points[index]); 

} 

graphics2D.draw(pen, polyline); 

x += gridWidth; 

graphics2D.setPenAndBrush(pen, brush); 

graphics2D.fill(null, 

new Rectangle(x, y, rectWidth, rectHeight)); 

graphics2D.draw(null, 

new Rectangle(x, y, rectWidth, rectHeight)); 

x = 5; 

y += gridHeight; 

stringY += gridHeight; 

Color[] colors = new Color[] { red, white }; 

int[] fractions = new int[] { 0, 255 }; 

LinearGradientBrush redtowhite 

= new LinearGradientBrush(x, y, x 

+ rectWidth, y, fractions, colors, 

com.mapdigit.drawing.Brush.NO_CYCLE); 

graphics2D.setPenAndBrush(pen, redtowhite); 

graphics2D.fill(null, new RoundRectangle(x, y, rectWidth, 

rectHeight, 

10, 10)); 

graphics2D.draw(null, new RoundRectangle(x, y, rectWidth, 

rectHeight, 

10, 10)); 

x += gridWidth; 

graphics2D.setPenAndBrush(pen, brush); 

graphics2D.fill(null, new Arc(x, y, rectWidth, 

rectHeight, 90, 135, 

Arc.CHORD)); 

graphics2D.draw(null, new Arc(x, y, rectWidth, 

rectHeight, 90, 135, 

Arc.CHORD)); 

x = 5; 

y += gridHeight; 

stringY += gridHeight; 

int x3Points[] = { x, x + rectWidth, x, x + rectWidth }; 

int y3Points[] = { y, y + rectHeight, y + rectHeight, y }; 

com.mapdigit.drawing.geometry.Path filledPolygon 

= new com.mapdigit.drawing.geometry.Path( 

com.mapdigit.drawing.geometry.Path.WIND_EVEN_ODD, 

x3Points.length); 

filledPolygon.moveTo(x3Points[0], y3Points[0]); 

for (int index = 1; index < x3Points.length; index++) { 

filledPolygon.lineTo(x3Points[index], y3Points[index]); 

} 

filledPolygon.closePath(); 

graphics2D.setPenAndBrush(pen, brush); 

graphics2D.fill(null, filledPolygon); 

graphics2D.draw(null, filledPolygon); 

} 
}