有关在Java中使用画布为Android绘制形状和路径的一些问题？

Question

How do I find the coordinates of the screen? I know eg a phone would have say a 960 x 540 resolution, but in the emulators some of the edges are not filled if I draw a shape to that resolution. Is there a way around this?

For the colour of the rectangle, it is seen there are two rectangles, and two of them have the same colour despite giving two separate colours for drawPaint. Just setting a new variable eg drawPaint2 returns errors. How to change the colour of both?

How to use the path function in the canvas. Eg to draw a triangle? I have included my attempt in the code but it doesn't display a triangle.

    public class DrawView extends View implements OnTouchListener
{

    private Paint backgroundPaint = new Paint();
    private Paint drawPaint = new Paint();
    private Paint circlePaint = new Paint();
    private Paint textPaint = new Paint();
    private Paint path = new Paint();
    private float sx, sy;

    public DrawView(Context context)
    {
        super(context);         

        setFocusable(true);
        setFocusableInTouchMode(true);

        backgroundPaint.setColor(Color.CYAN);
        backgroundPaint.setAntiAlias(true);
        backgroundPaint.setStyle(Style.FILL);

        drawPaint.setColor(Color.WHITE);
        drawPaint.setStyle(Style.FILL);

        circlePaint.setColor(Color.DKGRAY);
        circlePaint.setStyle(Style.FILL);

        textPaint.setColor(Color.WHITE);
        textPaint.setStyle(Style.FILL);

        drawPaint.setColor(Color.GREEN);
        drawPaint.setStyle(Style.FILL);

        circlePaint.setColor(Color.RED);
        circlePaint.setStyle(Style.FILL);

        path.setColor(android.graphics.Color.RED);
        path.setStyle(Paint.Style.FILL);            
        Path path = new Path();
        path.moveTo(1, 1);
        path.lineTo(20, 50);
        path.moveTo(20, 50);
        path.lineTo(100, 100);
        path.moveTo(100, 100);
        path.lineTo(1, 1);
        path.close();

        this.setOnTouchListener(this);
    }

    @Override
    public void onDraw(Canvas canvas)
    {

        //canvas.drawPath(path, paint); <-- error

        // to draw background
        canvas.drawRect(this.getLeft(), this.getTop(), this.getRight(), this.getBottom(), backgroundPaint);

        //to draw two rectangle with blue and green paint
        canvas.drawRect(100,100, 340,540, drawPaint); 
        canvas.drawRect(00,00, 120,80, drawPaint); 

        //draw text with paint
        canvas.drawText("Hello Dear Leader!", 110, 160, textPaint);

        //draw a circle with green paint with the touch coordinates
        canvas.drawCircle(sx-30,sy-30, 30, circlePaint);

        //draw a circle with red paint with the touch coordinates
        canvas.drawCircle(sx-80, sy-80, 10, circlePaint);

    }

    public boolean onTouch(View v, MotionEvent event)
    {   
        //update the coordinates for the OnDraw method above, with wherever we touch
        sx = event.getX();
        sy = event.getY();

        invalidate();
        return true;
    }

}

Answer 1

for the size you can easily call canvas.getWidth() and canvas.getHeight() and do all your values a percentage of those. Do never assume a constant!

You need to use two separate Paints to use two different colors. And remember that each paint is an object that needs initialisation.

// objects
private Paint drawPaint_WH = new Paint();
private Paint drawPaint_GR = new Paint();

// during construction
drawPaint_WH.setColor(Color.WHITE);
drawPaint_WH.setStyle(Style.FILL);

drawPaint_GR.setColor(Color. GREEN);
drawPaint_GR.setStyle(Style.FILL);

// and then during draw()
canvas.drawRect(100,100, 340,540, drawPaint_WH); 
canvas.drawRect(0,0, 120,80, drawPaint_GR); 

and then to make a triangle:

// object
private Path trianglePath;

// during construction
trianglePath = new Path();
trianglePath.moveTo(10, 10); // starting point
trianglePath.lineTo(10, 50); // 1st vertix
trianglePath.lineTo(50, 10); // 2nd vertix
trianglePath.lineTo(10, 10); // 3rd vertix and close

// then during draw()
canvas.drawPath(trianglePath, drawPaint_GR) // or whatever paint you want

ps.: do color the background it's easier to call canvas.drawColor(int colorVal);