Campass指南针绘制

public class CampassActivity extends Activity{

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		setContentView(R.layout.campass);
	}
}

campass.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:orientation="vertical" android:layout_width="fill_parent"
	android:layout_height="fill_parent">
	<com.gao.apidemo.view.CampassView 
		android:id="@+id/campass" android:orientation="vertical"
		android:layout_width="fill_parent" android:layout_height="fill_parent" />
</LinearLayout>

public class CampassView extends View{
	private Paint  mMarkerPaint;
	private Paint  mTextPaint;
	private Paint  mCirclePaint;
	private String mNorthText;
	private String mSouthText;
	private String mEastText;
	private String mWestText;
	private int    mTextHeight;
	

	public CampassView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		initView();
	}

	public CampassView(Context context, AttributeSet attrs) {
		super(context, attrs);
		initView();
	}

	public CampassView(Context context) {
		super(context);
		initView();
	}
	
	private void initView() {
		setFocusable(true);
		
		Resources resources=getResources();
		mNorthText=resources.getString(R.string.cardinal_north);
		mSouthText=resources.getString(R.string.cardinal_south);
		mEastText=resources.getString(R.string.cardinal_east);
		mWestText=resources.getString(R.string.cardinal_west);
		
		mCirclePaint=new Paint(Paint.ANTI_ALIAS_FLAG);
		mCirclePaint.setColor(resources.getColor(R.color.background_color));
		mCirclePaint.setStrokeWidth(1);
		mCirclePaint.setStyle(Style.FILL_AND_STROKE);
		
		mTextPaint=new Paint(Paint.ANTI_ALIAS_FLAG);
		mTextPaint.setColor(resources.getColor(R.color.text_color));
		mTextHeight=(int)mTextPaint.measureText("yY");
		
		mMarkerPaint=new Paint(Paint.ANTI_ALIAS_FLAG);
		mMarkerPaint.setColor(resources.getColor(R.color.marker_color));
	}
	
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		// The compass is a circle that fills as much space as possible.
	    // Set the measured dimensions by figuring out the shortest boundary,
	    // height or width.
		int measureWidth=measure(widthMeasureSpec);
		int measureHeight=measure(heightMeasureSpec);
		
		int d=Math.min(measureWidth, measureHeight);
		setMeasuredDimension(d, d);
	}

	private int measure(int measureSpec) {
		int result=0;
		 // Decode the measurement specifications.
		int specMode=MeasureSpec.getMode(measureSpec);
		int specSize=MeasureSpec.getSize(measureSpec);
		
		if (specMode==MeasureSpec.UNSPECIFIED) {
			result=200;
		}else {
			result=specSize;
		}
		return result;
	}
	
	@Override
	protected void onDraw(Canvas canvas) {
		int px=getMeasuredWidth()/2;
		int py=getMeasuredHeight()/2;
		
		int radius=Math.min(px, py);
		 // Draw the background
		canvas.drawCircle(px, py, radius, mCirclePaint);
		
		int textWidth=(int)mTextPaint.measureText("W");
		int cardinalX=px-textWidth/2;
		int cardinalY=py-radius+mTextHeight;
		
		// Draw the marker every 15 degrees and text every 45.
		for (int i = 0; i < 24; i++) {
			 // Draw a marker.
			canvas.drawLine(px, py-radius, px, py-radius+10, mMarkerPaint);
			canvas.save();
			canvas.translate(0,mTextHeight);
			// Draw the cardinal points
			if (i%6==0) {
				String dirText="";
				switch (i) {
				case 0:{
					dirText=mNorthText;
					int arrowY=2*mTextHeight;
					canvas.drawLine(px, arrowY, px-5, 3*mTextHeight, mTextPaint);
					canvas.drawLine(px, arrowY, px+5, 3*mTextHeight, mTextPaint);
				}
					break;
				case 6:
					dirText=mEastText;
					break;
				case 12:
					dirText=mSouthText;
					break;
				case 18:
					dirText=mWestText;
					break;
				default:
					break;
				}
				canvas.drawText(dirText, cardinalX, cardinalY, mTextPaint);
			}else if (i%3==0) {
				// Draw the text every alternate 45deg
				String angle=String.valueOf(15*i);
				int angleTextWidth=(int)mTextPaint.measureText(angle);
				int angleTextX=px-angleTextWidth/2;
				int angleTextY=py-radius+mTextHeight;
				canvas.drawText(angle, angleTextX, angleTextY, mTextPaint);
			}
			canvas.restore();
			canvas.rotate(15, px, py);
		}
	}
}

效果图：

在做的时候将

canvas.restore();
canvas.rotate(15, px, py);

写反了

canvas.rotate(15, px, py);
canvas.restore();

结果所有的数字和字母都画在了12点钟方向，也就是说我旋转了15度，但是马上就又restore恢复到了原来的角度。

canvas.rotate可以将这个看成是在没有旋转的情况下画，然后又旋转了相应的角度。