我想清除 Canvas 中所有绘制的内容。我尝试了多种方法，但还没有为我点击。如何使用清除按钮清除 Canvas 中的所有内容？
我有清除按钮来清除 Canvas android中的内容。但我显然不知道如何删除内容。我有撤消和重做按钮，除了这个清除按钮之外，它工作正常。有人可以告诉我如何使用这个清除按钮并删除内容？我的代码在这里。
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;
}
}
}
最佳答案
您应该避免实例化 paths再次调用clear()之前，否则您将调用clear()在空ArrayList :
((Button) findViewById(R.id.Clear)).setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
if (paths != null)
paths.clear();
if (dp != null)
dp.invalidate();
}
});
关于android - 如何使用按钮清除android中的 Canvas ？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22012550/