（转）Android--使用Canvas绘图

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/btn_resume"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="重新画图" />

        <Button
            android:id="@+id/btn_save"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="保存图片" />
    </LinearLayout>

    <ImageView
        android:id="@+id/iv_canvas"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

package cn.bgtx.canvasdemo;

import java.io.File;
import java.io.FileOutputStream;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private Button btn_save, btn_resume;
    private ImageView iv_canvas;
    private Bitmap baseBitmap;
    private Canvas canvas;
    private Paint paint;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 初始化一个画笔，笔触宽度为5，颜色为红色
        paint = new Paint();
        paint.setStrokeWidth(5);
        paint.setColor(Color.RED);

        iv_canvas = (ImageView) findViewById(R.id.iv_canvas);
        btn_save = (Button) findViewById(R.id.btn_save);
        btn_resume = (Button) findViewById(R.id.btn_resume);

        btn_save.setOnClickListener(click);
        btn_resume.setOnClickListener(click);
        iv_canvas.setOnTouchListener(touch);
    }

    private View.OnTouchListener touch = new OnTouchListener() {
        // 定义手指开始触摸的坐标
        float startX;
        float startY;

        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
            // 用户按下动作
            case MotionEvent.ACTION_DOWN:
                // 第一次绘图初始化内存图片，指定背景为白色
                if (baseBitmap == null) {
                    baseBitmap = Bitmap.createBitmap(iv_canvas.getWidth(),
                            iv_canvas.getHeight(), Bitmap.Config.ARGB_8888);
                    canvas = new Canvas(baseBitmap);
                    canvas.drawColor(Color.WHITE);
                }
                // 记录开始触摸的点的坐标
                startX = event.getX();
                startY = event.getY();
                break;
            // 用户手指在屏幕上移动的动作
            case MotionEvent.ACTION_MOVE:
                // 记录移动位置的点的坐标
                float stopX = event.getX();
                float stopY = event.getY();
                
                //根据两点坐标，绘制连线
                canvas.drawLine(startX, startY, stopX, stopY, paint);
                
                // 更新开始点的位置
                startX = event.getX();
                startY = event.getY();
                
                // 把图片展示到ImageView中
                iv_canvas.setImageBitmap(baseBitmap);
                break;
            case MotionEvent.ACTION_UP:

                break;
            default:
                break;
            }
            return true;
        }
    };
    private View.OnClickListener click = new OnClickListener() {

        @Override
        public void onClick(View v) {

            switch (v.getId()) {
            case R.id.btn_save:
                saveBitmap();
                break;
            case R.id.btn_resume:
                resumeCanvas();
                break;
            default:
                break;
            }
        }
    };

    /**
     * 保存图片到SD卡上
     */
    protected void saveBitmap() {
        try {
            // 保存图片到SD卡上
            File file = new File(Environment.getExternalStorageDirectory(),
                    System.currentTimeMillis() + ".png");
            FileOutputStream stream = new FileOutputStream(file);
            baseBitmap.compress(CompressFormat.PNG, 100, stream);
            Toast.makeText(MainActivity.this, "保存图片成功", 0).show();
            
            // Android设备Gallery应用只会在启动的时候扫描系统文件夹
            // 这里模拟一个媒体装载的广播，用于使保存的图片可以在Gallery中查看
            Intent intent = new Intent();
            intent.setAction(Intent.ACTION_MEDIA_MOUNTED);
            intent.setData(Uri.fromFile(Environment
                    .getExternalStorageDirectory()));
            sendBroadcast(intent);
        } catch (Exception e) {
            Toast.makeText(MainActivity.this, "保存图片失败", 0).show();
            e.printStackTrace();
        }
    }

    /**
     * 清除画板
     */
    protected void resumeCanvas() {
        // 手动清除画板的绘图，重新创建一个画板
        if (baseBitmap != null) {
            baseBitmap = Bitmap.createBitmap(iv_canvas.getWidth(),
                    iv_canvas.getHeight(), Bitmap.Config.ARGB_8888);
            canvas = new Canvas(baseBitmap);
            canvas.drawColor(Color.WHITE);
            iv_canvas.setImageBitmap(baseBitmap);
            Toast.makeText(MainActivity.this, "清除画板成功，可以重新开始绘图", 0).show();
        }
    }
}