android-API之FingerPaint手指绘图详解

主Activity类DemoViewPath.java

package com.geolo.android.demoViewPath;
import android.app.Activity;
import android.os.Bundle;
public class DemoViewPath extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        DemoPath dp = new DemoPath(this);
        setContentView(dp);
        super.onCreate(savedInstanceState);
    }
}

package com.geolo.android.demoViewPath; import android.app.Activity; import android.os.Bundle; public class DemoViewPath extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { DemoPath dp = new DemoPath(this); setContentView(dp); super.onCreate(savedInstanceState); } }  

 

绘图类：DemoPath.java

package com.geolo.android.demoViewPath;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.MotionEvent;
import android.view.View;
public class DemoPath extends View {
    private float mX , mY;
    private Path mPath;
    private Paint mPaint;
    private static final float TOUCH_TOLERANCE = 4;
    private Bitmap  mBitmap;
    private Canvas  mCanvas;
    private Paint   mBitmapPaint;

    public DemoPath(Context c) {
        super(c);

        mPaint = new Paint();//创建画笔渲染对象
        mPaint.setAntiAlias(true);//设置抗锯齿，让绘画比较平滑
        mPaint.setDither(true);//设置递色
        mPaint.setColor(0xFFFF0000);//设置画笔的颜色
        mPaint.setStyle(Paint.Style.STROKE);//画笔的类型有三种（1.FILL 2.FILL_AND_STROKE 3.STROKE ）
        mPaint.setStrokeJoin(Paint.Join.ROUND);//默认类型是MITER（1.BEVEL 2.MITER 3.ROUND ）
        mPaint.setStrokeCap(Paint.Cap.ROUND);//默认类型是BUTT（1.BUTT 2.ROUND 3.SQUARE ）
        mPaint.setStrokeWidth(12);//设置描边的宽度，如果设置的值为0那么边是一条极细的线

        mBitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);//绘制固定大小的bitmap对象
        mCanvas = new Canvas(mBitmap);//将固定的bitmap对象嵌入到canvas对象中
        mPath = new Path();//创建画笔路径
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawColor(0xFFAAAAAA);
        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        canvas.drawPath(mPath, mPaint);
        super.onDraw(canvas);
    }
    private void onTouchDown(float x , float y){
        mPath.reset();//将上次的路径保存起来，并重置新的路径。
        mPath.moveTo(x, y);//设置新的路径“轮廓”的开始
        mX = x;
        mY = y;
    }
    private void onTouchMove(float x , float y){
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
            mX = x;
            mY = y;
        }
    }
    private void onTouchUp(float x , float y){
        mPath.lineTo(mX, mY);//从最后一个指定的xy点绘制一条线，如果没有用moveTo方法，那么起始点表示（0，0）点。
        // commit the path to our offscreen
        mCanvas.drawPath(mPath, mPaint);//手指离开屏幕后，绘制创建的“所有”路径。
        // kill this so we don't double draw
        mPath.reset();
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN://手指开始按压屏幕，这个动作包含了初始化位置
            onTouchDown(x , y);
            invalidate();//刷新画布，重新运行onDraw（）方法
            break;
        case MotionEvent.ACTION_MOVE://手指按压屏幕时，位置的改变触发，这个方法在ACTION_DOWN和ACTION_UP之间。
            onTouchMove(x , y);
            invalidate();
            break;
        case MotionEvent.ACTION_UP://手指离开屏幕，不再按压屏幕
            onTouchUp(x , y);
            invalidate();
            break;
        default:
            break;
        }
        return true;
    }
}

package com.geolo.android.demoViewPath; import android.content.Context; import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Paint; import android.graphics.Path; import android.view.MotionEvent; import android.view.View; public class DemoPath extends View { private float mX , mY; private Path mPath; private Paint mPaint; private static final float TOUCH_TOLERANCE = 4; private Bitmap mBitmap; private Canvas mCanvas; private Paint mBitmapPaint; public DemoPath(Context c) { super(c); mPaint = new Paint();//创建画笔渲染对象 mPaint.setAntiAlias(true);//设置抗锯齿，让绘画比较平滑 mPaint.setDither(true);//设置递色 mPaint.setColor(0xFFFF0000);//设置画笔的颜色 mPaint.setStyle(Paint.Style.STROKE);//画笔的类型有三种（1.FILL 2.FILL_AND_STROKE 3.STROKE ） mPaint.setStrokeJoin(Paint.Join.ROUND);//默认类型是MITER（1.BEVEL 2.MITER 3.ROUND ） mPaint.setStrokeCap(Paint.Cap.ROUND);//默认类型是BUTT（1.BUTT 2.ROUND 3.SQUARE ） mPaint.setStrokeWidth(12);//设置描边的宽度，如果设置的值为0那么边是一条极细的线 mBitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);//绘制固定大小的bitmap对象 mCanvas = new Canvas(mBitmap);//将固定的bitmap对象嵌入到canvas对象中 mPath = new Path();//创建画笔路径 mBitmapPaint = new Paint(Paint.DITHER_FLAG); } @Override protected void onDraw(Canvas canvas) { canvas.drawColor(0xFFAAAAAA); canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint); canvas.drawPath(mPath, mPaint); super.onDraw(canvas); } private void onTouchDown(float x , float y){ mPath.reset();//将上次的路径保存起来，并重置新的路径。 mPath.moveTo(x, y);//设置新的路径“轮廓”的开始 mX = x; mY = y; } private void onTouchMove(float x , float y){ float dx = Math.abs(x - mX); float dy = Math.abs(y - mY); if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2); mX = x; mY = y; } } private void onTouchUp(float x , float y){ mPath.lineTo(mX, mY);//从最后一个指定的xy点绘制一条线，如果没有用moveTo方法，那么起始点表示（0，0）点。 // commit the path to our offscreen mCanvas.drawPath(mPath, mPaint);//手指离开屏幕后，绘制创建的“所有”路径。 // kill this so we don't double draw mPath.reset(); } @Override public boolean onTouchEvent(MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN://手指开始按压屏幕，这个动作包含了初始化位置 onTouchDown(x , y); invalidate();//刷新画布，重新运行onDraw（）方法 break; case MotionEvent.ACTION_MOVE://手指按压屏幕时，位置的改变触发，这个方法在ACTION_DOWN和ACTION_UP之间。 onTouchMove(x , y); invalidate(); break; case MotionEvent.ACTION_UP://手指离开屏幕，不再按压屏幕 onTouchUp(x , y); invalidate(); break; default: break; } return true; } }

 

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（1）在我们的应用中，无论绘制什么图形，我们只用到一个画笔。（如果我们将画笔的颜色设置为蓝色，我们画出的矩形、椭圆都将是蓝色的。）

（2）我们需要对画笔进行设置，然后所绘制的图形随之改变，而我们又不想在图形类的draw方法中“new”。

所以，我们需要应用单例模式，保证在我们的应用中只存在一个唯一的画笔实例。

单例画笔类Brush的源码如下：

package org.vhow.paintpad.tools;

import android.graphics.Paint;

/**
 * Use Singleton mode to create Brush class
 */
public class Brush extends Paint
{
    /**
     * Generate the instance when the class is loaded
     */
    private static Brush brush = new Brush();

    /**
     * Make the constructor private, to stop others to create instance by the
     * default constructor
     */
    private Brush()
    {
    }

    /**
     * Provide a static method that can be access by others.
     *
     * @return the single instance
     */
    public static Brush getPen()
    {
        return brush;
    }

    /**
     * reset the brush
     */
    public void reset()
    {
        brush.setAntiAlias(true);
        brush.setDither(true);
        brush.setColor(0xFF000000);
        brush.setStyle(Paint.Style.STROKE);
        brush.setStrokeJoin(Paint.Join.ROUND);
        brush.setStrokeCap(Paint.Cap.ROUND);
        brush.setStrokeWidth(2);
    }
}