随手涂鸦

随手涂鸦小示例：
xml布局文件：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

  <ImageView
      android:layout_width="match_parent"
      android:layout_height="0dp"
      android:layout_weight="1"
      android:id="@+id/imageView" />

  <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:orientation="horizontal">
      <Button
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="保存"
          android:onClick="save"/>
      <Button
          android:id="@+id/sb_red"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:text="清除"
          android:onClick="clear"/>

  </LinearLayout>
</LinearLayout>

Java功能代码：

public class MainActivity extends AppCompatActivity implements View.OnTouchListener {
private ImageView imageView;
private Bitmap bitmap;
private Canvas canvas;
//起始坐标
private int startX;
private int startY;
private Paint paint;    

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    imageView = findViewById(R.id.imageView);
    imageView.setOnTouchListener(this);
}     

@Override
public boolean onTouch(View view, MotionEvent event) {
    switch (event.getAction()){
        case MotionEvent.ACTION_DOWN:
            if (bitmap == null){
                bitmap = Bitmap.createBitmap(imageView.getWidth(),imageView.getHeight(),Bitmap.Config.ARGB_8888);
                canvas = new Canvas(bitmap);
                canvas.drawColor(Color.WHITE);
                paint = new Paint();
                paint.setColor(Color.RED); //画笔颜色为红色
                paint.setStrokeWidth(5);   //线条宽度5磅
            }
            startX = (int)event.getX();
            startY = (int)event.getY();
            break;
        case MotionEvent.ACTION_MOVE:
            int moveX = (int)event.getX();
            int moveY = (int)event.getY();
            canvas.drawLine(startX,startY,moveX,moveY,paint);
            imageView.setImageBitmap(bitmap);
            startX = moveX;
            startY = moveY;
            break;
            default:
                break;
    }
    return true;
}     

public void clear(View view){
   bitmap = null;
   imageView.setImageBitmap(null);
}    

public void save(View view){
   if (bitmap == null){
        Toast.makeText(this,"没有图片可以保存",Toast.LENGTH_LONG).show();
        return;
    }
    Log.i("path","path =" + getFilesDir());
    File file = new File(getFilesDir(),"pic"+System.currentTimeMillis()+".jpg");
    FileOutputStream stream = null;
    try{
        stream = new FileOutputStream(file);
        //以jpeg的图形格式将当前图片以流的形式输出
        boolean compress = bitmap.compress(Bitmap.CompressFormat.JPEG,100,stream);
        if (compress){
            Toast.makeText(this,"保存成功" + file.getAbsolutePath(),Toast.LENGTH_SHORT).show();
        }else{
            Toast.makeText(this,"保存失败",Toast.LENGTH_SHORT).show();
        }
    }catch (FileNotFoundException e){
        Toast.makeText(this,"保存失败" + e.getLocalizedMessage(),Toast.LENGTH_SHORT).show();
    }finally {
        if (stream != null){
            try{
                stream.close();
            }catch (IOException e){
                e.printStackTrace();
            }
        }
     }
  }
}

文件流的输入输出这块挺懵的，还需要再看看，此处表示从屏幕输出到内存，用的 FileOutputStream，其中存储路径getFilesDir()表示路径在 /data/data/包名/file/ 下。 希望用到的时候有的看，可以加些调色板啥的优化下。