Android开发笔记（十三）视图绘制的几个方法

import java.util.ArrayList;

import com.example.exmcustom.R;

import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

public class SignatureView extends View {
	private static final String TAG = "SignatureView";
	private Paint paint;
	private Canvas cacheCanvas;
	private Bitmap cachebBitmap;
	private Path path;
	private int paint_color = Color.BLACK;
	private int stroke_width = 3;
	private PathPosition pos = new PathPosition();
	private ArrayList<PathPosition> pathArray = new ArrayList<PathPosition>();
	private int mWidth=0, mHeight=0;

	public SignatureView(Context context,AttributeSet attrs) {
		super(context, attrs);
		if (attrs != null) {
        	TypedArray attrArray=getContext().obtainStyledAttributes( attrs, R.styleable.SignatureView);
        	paint_color = attrArray.getColor(R.styleable.SignatureView_paint_color, Color.BLACK);
        	stroke_width = attrArray.getInt(R.styleable.SignatureView_stroke_width, 3);
        	attrArray.recycle();
		}
	}
	
	public SignatureView(Context context, AttributeSet attrs, int defStyleAttr) {
		super(context, attrs, defStyleAttr);
		if (attrs != null) {
        	TypedArray attrArray=getContext().obtainStyledAttributes( attrs, R.styleable.SignatureView);
        	paint_color = attrArray.getColor(R.styleable.SignatureView_paint_color, Color.BLACK);
        	stroke_width = attrArray.getColor(R.styleable.SignatureView_stroke_width, 3);
        	attrArray.recycle();
		}
	}

	public SignatureView(Context context) {
		super(context);
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
		mWidth = this.getMeasuredWidth();
		mHeight = this.getMeasuredHeight();
		Log.d(TAG, "onMeasure width="+mWidth+",height="+mHeight);
		init(mWidth, mHeight);
	}
	
	public SignatureView(Context context, int width, int height) {
		super(context);
		init(width, height);
	}
	
	public int getPaintColor() {
		return paint_color;
	}
	
	public void setPaintColor(int paint_color) {
		this.paint_color = paint_color;
	}

	public int getStrokeWidth() {
		return stroke_width;
	}
	
	public void setStrokeWidth(int stroke_width) {
		this.stroke_width = stroke_width;
	}

	public Bitmap getCachebBitmap() {
		return getDrawingCache();
	}

	private void init(int width, int height) {
		paint = new Paint();
		paint.setAntiAlias(true);
		paint.setStrokeWidth(stroke_width);
		paint.setStyle(Paint.Style.STROKE);
		paint.setColor(paint_color);
		path = new Path();

		setDrawingCacheEnabled(true);
		cachebBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888);
		cacheCanvas = new Canvas(cachebBitmap);
		cacheCanvas.drawColor(Color.WHITE);
	}

	public void clear() {
		if (cacheCanvas != null) {
			pathArray.clear();
			cacheCanvas.drawRGB(255, 255, 255);
			invalidate();
		}
	}

	public void revoke() {
		if (pathArray.size() > 0) {
			pathArray.remove(pathArray.size()-1);
			cacheCanvas.drawRGB(255, 255, 255);
			for (int i=0; i<pathArray.size(); i++) {
				Path posPath = new Path();
				posPath.moveTo(pathArray.get(i).firstX, pathArray.get(i).firstY);
				posPath.quadTo(pathArray.get(i).firstX, pathArray.get(i).firstY, 
						pathArray.get(i).nextX, pathArray.get(i).nextY);
				cacheCanvas.drawPath(posPath, paint);
			}
			invalidate();
		}
	}

	@SuppressLint("DrawAllocation")
	@Override
	protected void onDraw(Canvas canvas) {
		canvas.drawBitmap(cachebBitmap, 0, 0, null);
		canvas.drawPath(path, paint); //这个是需要的，最近一次的路径保存在这里
	}

	private float cur_x, cur_y;

	@SuppressLint("ClickableViewAccessibility")
	@Override
	public boolean onTouchEvent(MotionEvent event) {

		float x = event.getX();
		float y = event.getY();

		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
			cur_x = x;
			cur_y = y;
			path.moveTo(cur_x, cur_y);
			pos.firstX = cur_x;
			pos.firstY = cur_y;
			break;
		case MotionEvent.ACTION_MOVE:
			path.quadTo(cur_x, cur_y, x, y);
			cur_x = x;
			cur_y = y;
			pos.nextX = cur_x;
			pos.nextY = cur_y;
			pathArray.add(pos);
			pos = new PathPosition();
			pos.firstX = cur_x;
			pos.firstY = cur_y;
			break;
		case MotionEvent.ACTION_UP:
			cacheCanvas.drawPath(path, paint);
			path.reset();
			break;
		}

		invalidate();
		return true;
	}
}