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"/