这是我第一次在 Android 中使用 Canvas 类。
我想要的是在画布上绘制不同颜色的线条。我有一个无法解决的问题。
在将颜色更改为红色并尝试用红色绘制第二条线后，我用黑色绘制第一条线，然后用黑色绘制的第一条线变为红色。
我使用的代码是：
import java.util.ArrayList;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.Pair;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
public class DrawView extends View implements OnTouchListener
{
private Canvas m_Canvas;
private Path m_Path;
private Paint m_Paint;
ArrayList<Pair<Path, Paint>> paths = new ArrayList<Pair<Path, Paint>>();
ArrayList<Pair<Path, Paint>> undonePaths = new ArrayList<Pair<Path, Paint>>();
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
// Bitmap canvasBackground;
public DrawView(Context context)
{
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
onCanvasInitialization();
}
public void onCanvasInitialization()
{
m_Paint = new Paint();
m_Paint.setAntiAlias(true);
m_Paint.setDither(true);
m_Paint.setColor(Color.parseColor("#37A1D1"));
m_Paint.setStyle(Paint.Style.STROKE);
m_Paint.setStrokeJoin(Paint.Join.ROUND);
m_Paint.setStrokeCap(Paint.Cap.ROUND);
m_Paint.setStrokeWidth(2);
m_Canvas = new Canvas();
m_Path = new Path();
Paint newPaint = new Paint(m_Paint);
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
// Bitmap canvas = BitmapFactory.decodeResource(getResources(), R.drawable.theme1_img_note).copy(Bitmap.Config.ARGB_8888, true);
// canvasBackground = Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Bitmap.Config.ARGB_8888 );
// m_Canvas = new Canvas(canvasBackground);
}
@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 (Pair<Path, Paint> p : paths)
{
canvas.drawPath(p.first, p.second);
}
}
public boolean onTouch(View arg0, MotionEvent event)
{
float x = event.getX();
float y = event.getY();
switch (event.getAction())
{
case MotionEvent.ACTION_DOWN:
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;
}
private void touch_start(float x, float y)
{
m_Path.reset();
m_Path.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)
{
m_Path.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
}
}
private void touch_up()
{
m_Path.lineTo(mX, mY);
// commit the path to our offscreen
m_Canvas.drawPath(m_Path, m_Paint);
// kill this so we don't double draw
m_Path = new Path();
Paint newPaint = new Paint(m_Paint); // Clones the mPaint object
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
}
public void onClickPenButton(int penWidth)
{
m_Paint.setStrokeWidth(penWidth);
m_Path = new Path();
Paint newPaint = new Paint(m_Paint); // Clones the mPaint object
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
}
public void onClickPenColorButton(int penColor)
{
m_Paint.setColor(penColor);
Paint newPaint = new Paint(m_Paint); // Clones the mPaint object
paths.add(new Pair<Path, Paint>(m_Path, newPaint));
}
public void onClickUndo ()
{
if (paths.size()>0)
{
undonePaths.add(paths.remove(paths.size()-1));
invalidate();
}
else
{
}
}
public void onClickRedo ()
{
if (undonePaths.size()>0)
{
paths.add(undonePaths.remove(undonePaths.size()-1));
invalidate();
}
else
{
}
}
}