Android画画板的制作方法

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_main"
  android:layout_width="match_parent" android:layout_height="match_parent"
  tools:context="com.example.demo.mainactivity">

  <imageview
    android:id="@+id/iv"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/bg"
    />

  <linearlayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:layout_alignparentbottom="true"
    >
    <button
      android:id="@+id/red"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="红色"
      android:onclick="onplay"
      />
    <button
      android:id="@+id/green"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="绿色"
      android:onclick="onplay"
      />
    <button
      android:id="@+id/root"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="刷子"
      android:onclick="onplay"
      />
    <button
      android:id="@+id/save"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="保存"
      android:onclick="onplay"
      />
    <button
      android:id="@+id/finish"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="涂漆"
      android:onclick="onplay"
      />
  </linearlayout>

</relativelayout>

/*
画板canvas  画板paint 手势识别器
整体思路:因为我是图片是作画,实际是对图片进行修改,起到画图的效果
1.原图,白纸,画笔,画板
2.根据手势识别进行作画

 */
public class mainactivity extends appcompatactivity {
private bitmap bitmap;
  private canvas canvas;
private imageview iv;
  private int startx;
  private int starty;
  private paint paint;
  private bitmap bmsrc;

  @override
  protected void oncreate(bundle savedinstancestate) {
    super.oncreate(savedinstancestate);
    setcontentview(r.layout.activity_main);
    //加载原图
    bmsrc = bitmapfactory.decoderesource(getresources(), r.drawable.bg);
    //创建白纸,宽,高,图片的参数
     bitmap = bitmap.createbitmap(bmsrc.getwidth(), bmsrc.getheight(), bmsrc.getconfig());
    //创建画板,参数是白纸对象
    canvas = new canvas(bitmap);
    //创建画笔
    paint = new paint();
    //在纸上作画
    iv=(imageview)findviewbyid(r.id.iv);
    canvas.drawbitmap(bmsrc,new matrix(), paint);
    //-----------------手势识别器和画笔结合的知识-------------------
  //给控件设置手势适配器,可以得到用户在这个控件上所做的手势
    iv.setontouchlistener(new view.ontouchlistener() {


      //当用户手在这个控件时,指的就是用户的手对控件滑动,按下,松开的三种场景,自动回调
      @override
      public boolean ontouch(view view, motionevent motionevent) {
        switch (motionevent.getaction()){
          case motionevent.action_down://按下时回调一次
            //获取用户手指按下时的坐标
            startx = (int) motionevent.getx();
            starty = (int) motionevent.gety();
            break;
          case motionevent.action_move://手指滑动时,不停地调用
            int newx = (int) motionevent.getx();
            int newy = (int) motionevent.gety();
            //在背景图画线
            canvas.drawline(startx,starty,newx,newy, paint);
            startx=newx;
            starty=newy;
            iv.setimagebitmap(bitmap);
            break;
          case motionevent.action_up://松开时回调一次

            break;
        }
        //事情分发机制
        //true:iv处理该触摸事件
        //false:iv不处理该触摸事件,事件传递给上一级
        return true;
      }
    });
  }
  public void onplay(view view){
   switch (view.getid()){
     case r.id.red:
       paint.setcolor(color.red);
       break;
     case r.id.green:
       paint.setcolor(color.green);
       break;
     case r.id.root:
       paint.setstrokewidth(5);
       break;
     case r.id.save:
       if(saveviewutil.savescreen(iv)){
         toast.maketext(this, "截图成功", toast.length_short).show();
       }else{
         toast.maketext(this, "截图失败，请检查sdcard是否可用", toast.length_short).show();
       }
       break;
     //涂漆
     case r.id.finish:
       canvas.drawrect(new rect(0,0,width,height), paint);
       break;
     }

   }
  }

public class saveviewutil {
  
  private static final file rootdir = new file(environment.getexternalstoragedirectory()+file.separator);

  /**保存截图的方法*/
  public static boolean savescreen(view view){
   //判断sdcard是否可用
   if(!environment.media_mounted.equals(environment.getexternalstoragestate())){
     return false;
   }
   if(!rootdir.exists()){
     rootdir.mkdir();
   }
   view.setdrawingcacheenabled(true);
   view.builddrawingcache();
   bitmap bitmap = view.getdrawingcache();
   try {
     bitmap.compress(compressformat.jpeg, 100, new fileoutputstream(new file(rootdir,system.currenttimemillis()+".jpg")));
     return true;
   } catch (filenotfoundexception e) {
     e.printstacktrace();
     return false;
   }finally{
     view.setdrawingcacheenabled(false);
     bitmap = null;
   }
  }
}
<!-- 往sdcard写入数据权限 -->
<uses-permission android:name="android.permission.write_external_storage"/>