Android实现简单画图画板

<RelativeLayout 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"
 tools:context=".MainActivity">
 <ImageView
  android:id="@+id/iv"
  android:layout_width="600px"
  android:layout_height="900px"
  android:layout_alignParentLeft="true"
  android:layout_alignParentRight="true"
  android:layout_alignParentStart="true" />
 <LinearLayout
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_alignParentBottom="true"
  android:layout_gravity="center_horizontal"
  android:orientation="horizontal">
  <Button
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:onClick="red"
   android:text="红色" />
  <Button
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:onClick="green"
   android:text="绿色"
    />
  <Button
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:onClick="brush"
   android:text="刷子"
   />
  <Button
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:onClick="eraser"
   android:text="橡皮擦"
    />
  <Button
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:onClick="save"
   android:text="保存" />
  <Button
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:onClick="cancel"
   android:text="取消" />
 </LinearLayout>
</RelativeLayout>

package com.example.yulongji.android10;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
public class MainActivity extends Activity {
 private ImageView iv;
 //原图
 private Bitmap bitsrc;
 //拷贝图
 private Bitmap bitcopy;
 private Canvas canvas;
 private Paint paint;
 private int startX;
 private int startY;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  iv = (ImageView) findViewById(R.id.iv);
  setBitmap();
  // 设置触摸侦听
  iv.setOnTouchListener(new View.OnTouchListener() {
   // 触摸屏幕时，触摸事件产生时，此方法调用
   @Override
   public boolean onTouch(View v, MotionEvent event) {
    int action = event.getAction();
    switch (action) {
     // 用户手指摸到屏幕
     case MotionEvent.ACTION_DOWN:
      startX = (int) event.getX();
      startY = (int) event.getY();
      break;
     // 用户手指正在滑动
     case MotionEvent.ACTION_MOVE:
      int x = (int) event.getX();
      int y = (int) event.getY();
      canvas.drawLine(startX, startY, x, y, paint);
      // 每次绘制完毕之后，本次绘制的结束坐标变成下一次绘制的初始坐标
      startX = x;
      startY = y;
      iv.setImageBitmap(bitcopy);
      break;
     // 用户手指离开屏幕
     case MotionEvent.ACTION_UP:
      break;
    }
    // true：告诉系统，这个触摸事件由我来处理
    // false：告诉系统，这个触摸事件我不处理，这时系统会把触摸事件传递给imageview的父节点
    return true;
   }
  });
 }
 public void setBitmap() {
  // 加载画画板的背景图
 bitsrc = BitmapFactory.decodeResource(getResources(), R.drawable.bg);
  // 创建图片副本
  // 1.在内存中创建一个与原图一模一样大小的bitmap对象，创建与原图大小一致的白纸
  bitcopy = Bitmap.createBitmap(bitsrc.getWidth(), bitsrc.getHeight(),
    bitsrc.getConfig());
  // 2.创建画笔对象
  paint = new Paint();
  // 3.创建画板对象，把白纸铺在画板上
  canvas = new Canvas(bitcopy);
  // 4.开始作画，把原图的内容绘制在白纸上
  canvas.drawBitmap(bitsrc, new Matrix(), paint);
  // 5.将绘制的图放入imageview中
  iv.setImageBitmap(bitcopy);
 }
 public void red(View view){
  paint.setColor(Color.RED);
 }
 public void green(View view){
  paint.setColor(Color.GREEN);
 }
 public void brush(View view){
  paint.setStrokeWidth(8);
 }
 public void cancel(View view){
  setBitmap();
 }
 public void eraser(View view){
  paint.setColor(Color.rgb(243,243,243));
  paint.setStrokeWidth(30);
 }
 public void save(View view){
  String path = Environment.getExternalStorageDirectory() + "/" + "2.png";
  File file = new File(path);
  try {
   FileOutputStream fos = new FileOutputStream(file);
   bitcopy.compress(Bitmap.CompressFormat.PNG, 100, fos);
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  }
  // 发送sd卡就绪广播
  Intent intent = new Intent();
  intent.setAction(Intent.ACTION_MEDIA_MOUNTED);
  intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));
  sendBroadcast(intent);
 }
}