Question

我正在制作用于教育的Android绘图应用程序，我几乎已经完成但我最后需要的是清除屏幕（画布）。我不知道怎么做，也做了一些研究，但凭借我的知识，我无法理解其中的一些。

public class SingleTouchEventView extends View {
  private Paint paint = new Paint();
  private Path path = new Path();

  public SingleTouchEventView(Context context, AttributeSet attrs) {
    super(context, attrs);

    paint.setAntiAlias(true);
    paint.setStrokeWidth(5f);
    paint.setColor(Color.BLACK);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeJoin(Paint.Join.ROUND);

  }

  @Override
  protected void onDraw(Canvas canvas) {
    canvas.drawPath(path, paint);
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    float eventX = event.getX();
    float eventY = event.getY();

    switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
      path.moveTo(eventX, eventY);
      return true;
    case MotionEvent.ACTION_MOVE:
      path.lineTo(eventX, eventY);
      break;
    case MotionEvent.ACTION_UP:
      // nothing to do
      break;
    default:
      return false;
    }

    // Schedules a repaint.
    invalidate();
    return true;
  }

  // KLEUR  switch statement
  void setColor(int i){

      switch (i){
         case 1:

             paint.setColor(Color.RED);

         break;

         case 2:

             paint.setColor(Color.BLUE);

         break;

         case 3:

             paint.setColor(Color.GREEN);

         break;

         default:

             paint.setColor(Color.BLACK);

         break;  

      }

    }
  // LIJN DIKTE  switch statement
  void setStrokeWidth(int k){

      switch (k){
         case 5:

             paint.setStrokeWidth(12f);

         break;

         case 4:

             paint.setStrokeWidth(5f);

         break;

        default:

             paint.setStrokeWidth(5f);

         break;  

      }

    }
}

上面的代码是SingleTouchEventView.java

以下代码是主要的SingleTouchActivity.java

public class SingleTouchActivity extends Activity {

    @Override

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

      }

    @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;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
         SingleTouchEventView stev = new SingleTouchEventView(this, null);
            setContentView(stev);
            // Handle action bar item clicks here. The action bar will
            // automatically handle clicks on the Home/Up button, so long
            // as you specify a parent activity in AndroidManifest.xml.

            int id = item.getItemId();
            if (id == R.id.action_settings) {
                    return true;
            }
            if (id == R.id.ResetAction) {

                    return true;
            }if (id == R.id.LijnDun) {
                stev.setStrokeWidth(4);
                    return true;
            }if (id == R.id.LijnDik) {
                stev.setStrokeWidth(5);
                    return true;
            }
            if (id == R.id.LijnGroen) {
                stev.setColor(3);//GROEN
                    return true;
            }
            if (id == R.id.LijnBlauw) {
                    stev.setColor(2);//for blue color
                    return true;
            }
            if (id == R.id.LijnRood) {
                       stev.setColor(1);//for red color

                       return true;
            }

            return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.main_fragment, container,
                    false);
            return rootView;
        }
    }

}

在SingleTouchActivity.Java中我有一个id为ResetAction的menuitem 每当我点击菜单项中的那个我想清除画布。我希望有人能够帮助我，我也为我糟糕的英语道歉，而不是我的母语

Answer 1

path.reset()应该在您执行下一次重绘后清理画布。

所以只需将此方法添加到SingleTouchEventView类

即可

public void reset() {
    path.reset();
}

但是，您创建了一个新的SingleTouchEventView实例，它创建了不同的绘制实例。我建议您使用单个SingleTouchEventView实例来管理整个画布而不是多个实例。如果没有，则调用reset（）只会清除上次创建实例时绘制的内容。虽然，如果这是您想要的行为，那么您至少需要跟踪您在列表中创建的每个实例，以便在需要时更改它们。

清除画布与菜单项onclick android

1 个答案: