如何在android中使用按鈕清除畫布？

Question

我想清除畫布中的所有繪製內容。我嘗試了幾種方法，但還沒有爲我點擊過。如何清除canvas中使用清除按鈕的所有內容？

我有明確的按鈕清除畫布android.But內容，但我清楚不知道如何刪除內容。我有撤消和重做按鈕，這是工作正常，除了這個清除按鈕。有人告訴我如何使用此清除按鈕並刪除內容？我的代碼在這裏。

public class MainActivity extends Activity { 

    private ArrayList<Path> undonePaths = new ArrayList<Path>(); 
    private ArrayList<Path> paths = new ArrayList<Path>(); 
    /* 
    * private Button alphabetsButton; private Button lettersButton; private 
    * Button clearButton; 
    */ 
    private FrameLayout frmLayout; 
    Canvas canvas; 

    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     frmLayout = (FrameLayout) findViewById(R.id.frameLayout); 
     final DrawingPanel dp = new DrawingPanel(MainActivity.this); 
     frmLayout.addView(dp); 

     /* 
     * alphabetsButton=(Button) findViewById(R.id.button1); 
     * lettersButton=(Button) findViewById(R.id.button2); 
     * 
     * 
     * 
     * alphabetsButton.setOnClickListener(new OnClickListener() { 
     * 
     * @Override public void onClick(View v) { // TODO Auto-generated method 
     * stub startActivity(new Intent(MainActivity.this,Letters.class)); 
     * finish(); } }); 
     */ 

     ((Button) findViewById(R.id.Clear)).setOnClickListener(new OnClickListener() { 

      @Override 
      public void onClick(View v) { 

       paths = new ArrayList<Path>(); 
       paths.clear(); 

      } 
     }); 

     ((Button) findViewById(R.id.Undo)).setOnClickListener(new OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       if (paths.size() > 0) { 
        undonePaths.add(paths.remove(paths.size() - 1)); 
        dp.invalidate(); 
       } 
      } 
     }); 

     ((Button) findViewById(R.id.Redo)).setOnClickListener(new OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       // TODO Auto-generated method stub 
       if (undonePaths.size() > 0) { 
        paths.add(undonePaths.remove(undonePaths.size() - 1)); 
        dp.invalidate(); 
       } 
      } 
     }); 
    } 

    class DrawingPanel extends View implements OnTouchListener { 

     private Canvas mCanvas; 
     private Path mPath; 
     private Paint mPaint, circlePaint, outercirclePaint; 
     private Bitmap mBitmap; 
     private int width; 
     private int height; 

     // private ArrayList<Path> undonePaths = new ArrayList<Path>(); 
     private float xleft, xright, xtop, xbottom; 

     public DrawingPanel(Context context) { 
      super(context); 
      setFocusable(true); 
      setFocusableInTouchMode(true); 
      this.setOnTouchListener(this); 
      circlePaint = new Paint(); 
      mPaint = new Paint(); 
      outercirclePaint = new Paint(); 
      outercirclePaint.setAntiAlias(false); 
      circlePaint.setAntiAlias(false); 
      mPaint.setAntiAlias(false); 
      mPaint.setColor(0xFF000000); 
      outercirclePaint.setColor(0x44FFF000); 
      circlePaint.setColor(0xF57F35); 
      outercirclePaint.setStyle(Paint.Style.FILL_AND_STROKE); 
      circlePaint.setStyle(Paint.Style.FILL); 
      mPaint.setStyle(Paint.Style.STROKE); 
      mPaint.setStrokeJoin(Paint.Join.MITER); 
      mPaint.setStrokeCap(Paint.Cap.ROUND); 
      mPaint.setStrokeWidth(20); 
      outercirclePaint.setStrokeWidth(15); 
      mCanvas = new Canvas(); 
      mPath = new Path(); 
      paths.add(mPath); 
     } 

     public void colorChanged(int color) { 
      mPaint.setColor(color); 
     } 

     @Override 
     protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
      super.onSizeChanged(w, h, oldw, oldh); 
     } 

     @Override 
     protected void onDraw(Canvas canvas) { 

      for (Path p : paths) { 
       canvas.drawPath(p, mPaint); 
      } 

     } 

     private float mX, mY; 
     private static final float TOUCH_TOLERANCE = 0; 

     private void touch_start(float x, float y) { 
      mPath.reset(); 
      mPath.moveTo(x, y); 
      mX = x; 
      mY = y; 
     } 



     private void touch_move(float x, float y) { 
      float dx = Math.abs(x - mX); 
      float dy = Math.abs(y - mY); 
      if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { 
       mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2); 
       mX = x; 
       mY = y; 
      } 
     } 

     private void touch_up() { 
      mPath.lineTo(mX, mY); 
      // commit the path to our offscreen 
      mCanvas.drawPath(mPath, mPaint); 
      // kill this so we don't double draw 
      mPath = new Path(); 
      paths.add(mPath); 
     } 

     @Override 
     public boolean onTouch(View arg0, MotionEvent event) { 
      float x = event.getX(); 
      float y = event.getY(); 

      switch (event.getAction()) { 
      case MotionEvent.ACTION_DOWN: 
       // if (x <= cx+circleRadius+5 && x>= cx-circleRadius-5) { 
       // if (y<= cy+circleRadius+5 && cy>= cy-circleRadius-5){ 
       // paths.clear(); 
       // return true; 
       // } 
       // } 
       touch_start(x, y); 
       invalidate(); 
       break; 
      case MotionEvent.ACTION_MOVE: 
       touch_move(x, y); 
       invalidate(); 
       break; 
      case MotionEvent.ACTION_UP: 
       touch_up(); 
       invalidate(); 
       break; 
      } 
      return true; 
     } 
    } 

} 

Answer 1

貌似路徑數組列表堅持，試試這個代碼：

private ArrayList<Path> _graphics = new ArrayList<Path>() 

@Override 
public void onClick(View v) { 
     clear(); 
} 


Bitmap mBitmap; 
Paint mPaint; 
Canvas mCanvas; 
int width,height; 

public void clear() 
{ 
    _graphics.removeAll(_graphics); 
    mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888); 
    path = new Path(); 
    invalidate(); 
} 

Answer 2

可能你應該避免再次調用clear()之前實例paths，否則你會在一個空ArrayList撥打clear()：

((Button) findViewById(R.id.Clear)).setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      if (paths != null) 
       paths.clear(); 
      if (dp != null) 
       dp.invalidate(); 
     } 
    }); 

Answer 3

你可以試試這個：

@Override 
public void onClick(DialogInterface dialog, int which) { 
    mCanvas.drawColor(0, PorterDuff.Mode.CLEAR); 
    //paths.clear(); 
    //.destroyDrawingCache(); 
    mPath.reset(); 
    dp.invalidate(); 
}