Android简明开发教程十三：Option Menu 画笔示例

引路蜂二维图形画笔（Pen）示例含有四个示例，Lines ，Dashes ,LineJoin 和LineCap。打算采用Option Menu（主菜单）的方式来选择不同示例。

首先要对GuidebeeGraphics2DView，和Graphics2DActivity做些改动，从这个示例开始，GuidebeeGraphics2DView需要动态绘制不同图形（可以通过菜单，或是Thread）。在GuidebeeGraphics2DView增加下面两个方法：

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final Runnable updateCanvas = new Runnable() { public void run() { invalidate(); } }; public void refreshCanvas(){ post(updateCanvas); }

post可以用在非UI Thread中Call UI Thread中方法。这里只是触发屏幕重绘事件以刷新屏幕显示。

在Graphics2DActivity增加一个变量protected GuidebeeGraphics2DView graphic2dView; 来获得对应的GuidebeeGraphics2DView实例。

graphic2dView=(GuidebeeGraphics2DView)findViewById(R.id.graphics2dview);

使用Option Menu，尽管也可以完全使用代码来创建菜单，更一般的方法是使用菜单资源。在res 下创建menu 子目录，然后在res/menu下创建menu_option_line.xml 用来显示Pen的四个示例选项：

<?xml version=”1.0″ encoding=”utf-8″?>
<menu
xmlns:android=”http://schemas.android.com/apk/res/android“>
<item
android:id=”@+id/mnuLines”
android:title=”Lines”
android:icon=”@drawable/icon1″>
</item>
<item
android:id=”@+id/mnuDashes”
android:title=”Dashes”
android:icon=”@drawable/icon2″>
</item>
<item
android:id=”@+id/mnuLineCap”
android:title=”LineCap”
android:icon=”@drawable/icon3″>
</item>
<item
android:id=”@+id/mnuLineJoin”
android:title=”LineJoin”
android:icon=”@drawable/icon4″>
</item>
</menu>

<menu></menu> 定义菜单，<item></item>定义菜单项，<item></item>可以嵌套以定义子菜单。菜单可以定义id, Icon,Text等属性。也可以支持单选，多选，此时就需要借助<group></group>,使用group可以把一最菜单项定义为一个组，可以使用setGroupVisible()来显示隐藏整个菜单组，Enable 或是Disable整个菜单组setGroupEnabled()等。最关键的，有了组才能实现菜单的单选和多选功能：

<?xml version=”1.0″ encoding=”utf-8″?>
<menu xmlns:android=”http://schemas.android.com/apk/res/android“>
<item android:id=”@+id/item1″
android:icon=”@drawable/item1″
android:title=”@string/item1″ />
<!– menu group –>
<group android:id=”@+id/group1″>
<item android:id=”@+id/groupItem1″
android:title=”@string/groupItem1″ />
<item android:id=”@+id/groupItem2″
android:title=”@string/groupItem2″ />
</group>
</menu>

定义好菜单资源后，就可以使用MenuInflater.inflate()展开菜单，一般需要在Activity的onCreateOptionsMenu()展开菜单：

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@Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.menu_option_line, menu); return true; }

最后是响应菜单事件：

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@Override public boolean onOptionsItemSelected(MenuItem item) { menuOption = item.getItemId(); drawImage(); return true; }

item.getItemId(); 返回菜单的ID（在菜单资源中定义）。

完整代码如下：

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public class Pen extends Graphics2DActivity { int menuOption; @Override protected void drawImage() { switch (menuOption) { case R.id.mnuLines: drawLines(); break; case R.id.mnuDashes: drawDash(); break; case R.id.mnuLineCap: drawLineCap(); break; case R.id.mnuLineJoin: drawLineJoin(); break; default: drawLines(); break; } graphic2dView.refreshCanvas(); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.menu_option_line, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { menuOption = item.getItemId(); drawImage(); return true; } private void drawLineJoin() { Color blackColor = new Color(0xff000000); Color whiteColor = new Color(0xffffffff); com.mapdigit.drawing.geometry.Path path = new com.mapdigit.drawing.geometry.Path(); path.moveTo(40, 60); path.lineTo(90, 20); path.lineTo(140, 60); // Clear the canvas with white color. graphics2D.clear(Color.WHITE); AffineTransform matrix = new AffineTransform(); graphics2D.setAffineTransform(matrix); com.mapdigit.drawing.Pen pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_BUTT, com.mapdigit.drawing.Pen.JOIN_MITER); graphics2D.draw(pen, path); pen = new com.mapdigit.drawing.Pen(whiteColor, 1); graphics2D.draw(pen, path); matrix.translate(0, 50); graphics2D.setAffineTransform(matrix); pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_BUTT, com.mapdigit.drawing.Pen.JOIN_ROUND); graphics2D.draw(pen, path); pen = new com.mapdigit.drawing.Pen(whiteColor, 1); graphics2D.draw(pen, path); matrix = new AffineTransform(); matrix.translate(0, 100); graphics2D.setAffineTransform(matrix); pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_BUTT, com.mapdigit.drawing.Pen.JOIN_BEVEL); graphics2D.draw(pen, path); pen = new com.mapdigit.drawing.Pen(whiteColor, 1); graphics2D.draw(pen, path); } private void drawLineCap() { Color blackColor = new Color(0xff000000); Color whiteColor = new Color(0xffffffff); // Clear the canvas with white color. graphics2D.clear(Color.WHITE); AffineTransform matrix = new AffineTransform(); graphics2D.setAffineTransform(matrix); com.mapdigit.drawing.Pen pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_BUTT, com.mapdigit.drawing.Pen.JOIN_MITER); graphics2D.drawLine(pen, 40, 60, 140, 60); pen = new com.mapdigit.drawing.Pen(whiteColor, 1); graphics2D.drawLine(pen, 40, 60, 140, 60); pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_ROUND, com.mapdigit.drawing.Pen.JOIN_MITER); graphics2D.drawLine(pen, 40, 100, 140, 100); pen = new com.mapdigit.drawing.Pen(whiteColor, 1); graphics2D.drawLine(pen, 40, 100, 140, 100); pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_SQUARE, com.mapdigit.drawing.Pen.JOIN_MITER); graphics2D.drawLine(pen, 40, 140, 140, 140); pen = new com.mapdigit.drawing.Pen(whiteColor, 1); graphics2D.drawLine(pen, 40, 140, 140, 140); } private void drawLines() { Color greenColor = new Color(0xff00ff00); // Clear the canvas with white color. graphics2D.clear(Color.WHITE); AffineTransform matrix = new AffineTransform(); graphics2D.setAffineTransform(matrix); com.mapdigit.drawing.Pen pen = new com.mapdigit.drawing.Pen(greenColor,1); graphics2D.drawLine(pen, 20, 150, 60, 50); pen = new com.mapdigit.drawing.Pen(greenColor, 2); graphics2D.drawLine(pen, 40, 150, 80, 50); pen = new com.mapdigit.drawing.Pen(greenColor, 3); graphics2D.drawLine(pen, 60, 150, 100, 50); pen = new com.mapdigit.drawing.Pen(greenColor, 5); graphics2D.drawLine(pen, 80, 150, 120, 50); pen = new com.mapdigit.drawing.Pen(greenColor, 7); graphics2D.drawLine(pen, 100, 150, 140, 50); pen = new com.mapdigit.drawing.Pen(greenColor, 10); graphics2D.drawLine(pen, 120, 150, 160, 50); } private void drawDash() { Color blackColor = new Color(0xff000000); int dashArray1[] = { 2, 2 }; int dashArray2[] = { 6, 6 }; int dashArray3[] = { 4, 1, 2, 1, 1, 6 }; // Clear the canvas with white color. graphics2D.clear(Color.WHITE); AffineTransform matrix = new AffineTransform(); graphics2D.setAffineTransform(matrix); com.mapdigit.drawing.Pen pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_BUTT, com.mapdigit.drawing.Pen.JOIN_MITER, dashArray1, 0); graphics2D.drawLine(pen, 40, 60, 140, 60); pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_BUTT, com.mapdigit.drawing.Pen.JOIN_MITER, dashArray2, 0); graphics2D.drawLine(pen, 40, 100, 140, 100); pen = new com.mapdigit.drawing.Pen(blackColor, 20, com.mapdigit.drawing.Pen.CAP_BUTT, com.mapdigit.drawing.Pen.JOIN_MITER, dashArray3, 0); graphics2D.drawLine(pen, 40, 140, 140, 140); } }