绘图时预览绘制直线

Question

我有一个绘制线条的应用程序。当我按下屏幕时，斜杠并停止触摸，它会画一条线。我想知道当我在屏幕上削减手指时，如何看到我画的线。

这是我绘制线条的代码：

public class DrawingView extends View {

    private Path drawPath;
    private Paint drawPaint;
    private Paint canvasPaint;
    private int paintColor=Color.BLACK;
    private Canvas drawCanvas;
    private Bitmap canvasBitmap;
    float tX;
    float tY;

    public DrawingView(Context context, AttributeSet attrs){
        super(context, attrs);
        setupDrawing();
    }

    private void setupDrawing(){
        drawPath=new Path();
        drawPaint=new Paint();
        drawPaint.setColor(paintColor);
        drawPaint.setAntiAlias(true);
        drawPaint.setStrokeWidth(1);
        drawPaint.setStyle(Paint.Style.STROKE);
        drawPaint.setStrokeJoin(Paint.Join.ROUND);
        drawPaint.setStrokeCap(Paint.Cap.ROUND);
        canvasPaint=new Paint(Paint.DITHER_FLAG);
    }

    protected void onSizeChanged(int w, int h, int oldw, int oldh){
        super.onSizeChanged(w, h, oldw, oldh);
        canvasBitmap=Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        drawCanvas=new Canvas(canvasBitmap);
    }


    protected void onDraw(Canvas canvas){
        canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
        canvas.drawPath(drawPath, drawPaint);  
    }  

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

    private void touch_up(){
        drawPath.lineTo(mX, mY);
        drawCanvas.drawPath(drawPath, drawPaint);
        drawPath.reset();
    }

    public boolean onTouchEvent(MotionEvent event){
        tX=event.getX();
        tY=event.getY();
        switch(event.getAction()){
            case MotionEvent.ACTION_DOWN:
                touch_start(tX,tY);
            break;
            case MotionEvent.ACTION_MOVE:
                touch_move(tX,tY);
            break;
            case MotionEvent.ACTION_UP:
                touch_up();
            break;
            default:
                return false;
        }
        invalidate();
        return true;
    }
}

Answer 1

public class DrawingView extends View {

    private static final float TOUCH_TOLERANCE = 0;
    private Path drawPath;
    private Paint drawPaint;
    private Paint canvasPaint;
    private int paintColor=Color.BLACK;
    private Canvas drawCanvas;
    private Bitmap canvasBitmap;
    float tX;
    float tY;
    private float mX;
    private float mY;

    private float a,b;

    public DrawingView(Context context, AttributeSet attrs){
        super(context, attrs);
        setupDrawing();
    }

    private void setupDrawing(){
        drawPath=new Path();
        drawPaint=new Paint();
        drawPaint.setColor(paintColor);
        drawPaint.setAntiAlias(true);
        drawPaint.setStrokeWidth(1);
        drawPaint.setStyle(Paint.Style.STROKE);
        drawPaint.setStrokeJoin(Paint.Join.ROUND);
        drawPaint.setStrokeCap(Paint.Cap.ROUND);
        canvasPaint=new Paint(Paint.DITHER_FLAG);
    }

    protected void onSizeChanged(int w, int h, int oldw, int oldh){
        super.onSizeChanged(w, h, oldw, oldh);
        canvasBitmap=Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        drawCanvas=new Canvas(canvasBitmap);
    }


    protected void onDraw(Canvas canvas){
        canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
        canvas.drawPath(drawPath, drawPaint);  
    }  

    private void touch_start(float x, float y){
        drawPath.reset();
        drawPath.moveTo(x, y);
        mX=x;
        mY=y;
        a=x;
        b=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){
            mX=x;
            mY=y;
        }
        drawPath.lineTo(mX, mY);
        //invalidate();
    }

    private void touch_up(float tX2, float tY2){
        drawPath.lineTo(mX, mY);
        //drawCanvas.drawPath(drawPath, drawPaint);
        drawCanvas.drawLine(a, b, tX2, tY2, drawPaint);
        drawPath.reset();
    }

    public boolean onTouchEvent(MotionEvent event){
        tX=event.getX();
        tY=event.getY();
        switch(event.getAction()){
            case MotionEvent.ACTION_DOWN:
                touch_start(tX,tY);
            break;
            case MotionEvent.ACTION_MOVE:
                touch_move(tX,tY);
            break;
            case MotionEvent.ACTION_UP:
                touch_up(tX,tY);
            break;
            default:
                return false;
        }
        invalidate();
        return true;
    }
}

请试试这个......