public class MainActivity extends Activity {

	private ImageView iv;

	float startX = 0;

	float startY = 0;

	//获得一个能够被bitmap

	Bitmap bitmap = Bitmap.createBitmap(400, 400,Bitmap.Config.ARGB_8888);

	//创建画布

	Canvas canvas = new Canvas(bitmap);

	//创建画笔

	Paint paint = new Paint();

	@Override

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);

		setContentView(R.layout.activity_main);

		iv = (ImageView) this.findViewById(R.id.iv);

		paint.setColor(Color.BLACK);

		paint.setStrokeWidth(1);//设置像素

		iv.setOnTouchListener(new OnTouchListener() {

			@Override

			public boolean onTouch(View v, MotionEvent event) {

				switch (event.getAction()) {

					case MotionEvent.ACTION_DOWN:

						startX = event.getX();

						startY = event.getY();

						break;

					case MotionEvent.ACTION_MOVE:

						float newX = event.getX();

						float newY = event.getY();

						canvas.drawLine(startX, startY, newX, newY, paint);

						iv.setImageBitmap(bitmap);

						break;

					case MotionEvent.ACTION_UP:

						break;

					default:

						break;

				}

				return true;

			}

		});

	}

	@Override

	public boolean onCreateOptionsMenu(Menu menu) {

		// Inflate the menu; this adds items to the action bar if it is present.

		getMenuInflater().inflate(R.menu.main, menu);

		return true;

	}

}