在Activity中添加可拖动视图

public class MainActivity extends Activity {
    private int screenWidth;
    private int screenHeight;
    private ImageView iv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        iv = (ImageView) findViewById(R.id.iv);
        iv.setOnTouchListener(movingEventListener);
        DisplayMetrics dm = getResources().getDisplayMetrics();
        screenWidth = dm.widthPixels;
        screenHeight = dm.heightPixels - 50;

    }

    private OnTouchListener movingEventListener = new OnTouchListener() {
        int lastX, lastY;

        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
            // 触控笔按下
            case MotionEvent.ACTION_DOWN:
                Toast.makeText(MainActivity.this, "ACTION_DOWN", 1).show();
                Log.e("11111111111:", "ACTION_DOWN");
                // 得到X坐标
                lastX = (int) event.getRawX();
                // 得到Y坐标
                lastY = (int) event.getRawY();
                break;
            // 触控笔移动
            case MotionEvent.ACTION_MOVE:
                int dx = (int) event.getRawX() - lastX;
                int dy = (int) event.getRawY() - lastY;

                int left = v.getLeft() + dx;
                int top = v.getTop() + dy;
                int right = v.getRight() + dx;
                int bottom = v.getBottom() + dy;
                // 设置不能出界
                if (left < 0) {
                    left = 0;
                    right = left + v.getWidth();
                }

                if (right > screenWidth) {
                    right = screenWidth;
                    left = right - v.getWidth();
                }

                if (top < 0) {
                    top = 0;
                    bottom = top + v.getHeight();
                }

                if (bottom > screenHeight) {
                    bottom = screenHeight;
                    top = bottom - v.getHeight();
                }

                v.layout(left, top, right, bottom);

                lastX = (int) event.getRawX();
                lastY = (int) event.getRawY();
                Log.e("222222222:", "ACTION_MOVE");
                break;
            case MotionEvent.ACTION_UP:
                Toast.makeText(MainActivity.this, "ACTION_UP", 1).show();
                Log.e("333333333333:", "ACTION_UP");
                break;
            }
            return true;
        }
    };

}

 可参考：http://blog.csdn.net/qqtubo/article/details/8657242