如何在按钮单击时清除android中的画布

Question

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

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

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

  paint.setAntiAlias(true);
  paint.setStrokeWidth(18f);
  paint.setColor(Color.LTGRAY);
  paint.setStyle(Paint.Style.STROKE);
  paint.setStrokeJoin(Paint.Join.ROUND);
  paint.setStrokeCap(Paint.Cap.ROUND);
}

@Override
protected void onDraw(Canvas canvas) {
    if(cc)
    {
        Bitmap back = BitmapFactory.decodeResource(getResources(), R.drawable.black_square);
        Bitmap cb = Bitmap.createScaledBitmap(back, 0, 0, false);
        canvas.drawBitmap(cb,0,0,null);
        cc = false;

    }
  canvas.drawPath(path, paint);
}

public void clearCanvas()
{
  cc =true;
  invalidate();
}

@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;
  }
} 

The above file is my SingleTouchEventView.Java Here is my MainActivity.java

public class MainActivity extends Activity {

    Button reset;;
LinearLayout canvasAlphabets;
    SingleTouchEventView myView; 


   @Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);


    reset = (Button)findViewById(R.id.reset_canvas);

    myView = new SingleTouchEventView(this, null);
    canvasAlphabets = (LinearLayout)findViewById(R.id.canvas_Alphabets);
    canvasAlphabets.addView(myView);


           reset.setOnClickListener(new View.OnClickListener() {


        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub


        }
        });

      }

  }

My question is what code should I use in reset button to delete all contents of canvas. Please help me I have tried implementing myView.clearCanvas() but that doesn't help. If I add this code to reset buutons on Click it causes FC

Thanks

Answer 1

 path = new Path(); 
 Paint clearPaint = new Paint(); 
 clearPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
 canvas.drawRect(0, 0, 0, 0, clearPaint); 
 cc = false; 

I got it fixed with above code

Answer 2

Maybe I do not understand what you want to draw, but have you tried this:

protected void onDraw(Canvas canvas) 
{
    if (cc)
    {
        Bitmap back = BitmapFactory.decodeResource(getResources(), R.drawable.black_square);
        Bitmap cb = Bitmap.createScaledBitmap(back, 0, 0, false);
        canvas.drawBitmap(cb,0,0,null);
        cc = false;
    } 
    else
        canvas.drawPath(path, paint);
    }
}

Otherwise, if you want to erase all, you can use this new paint:

Paint transparent = new Paint();
transparent.setAlpha(0);

Answer 3

您可以使用透明颜色对所有内容进行平移，以清除所有内容。