Question

我是Android图形编程的新手。我想在我的画布中心放置一个位图。因此，我使用：

public void onDraw(Canvas canvas) {
    float canvasx = (float) canvas.getWidth();
    float canvasy = (float) canvas.getHeight();

然后我调用我想要使用的位图，

Bitmap myBitmap = BitmapFactory.decodeResource(getResources(),
        R.drawable.myBitmap);

然后我通过使用

找到我的位图的坐标位置

float bitmapx = (float) myBitmap.getWidth();
float bitmapy = (float) myBitmap.getHeight();

float boardPosX = (canvasx - bitmapx) / 2;
float boardPosY = (canvasy - bitmapy) / 2;

最后，我使用

绘制位图

canvas.drawBitmap(myBitmap, boardPosX, boardPosY, null);

但是，位图不在画布的中心。它略低于我认为应该成为画布中心的位置。

在onDraw（）方法中获取画布高度和宽度是否正确？知道什么是错的吗？提前谢谢。

*编辑：

最后，我通过改变

使其发挥作用

public void onDraw(Canvas canvas) {
    float canvasx = (float) canvas.getWidth();
    float canvasy = (float) canvas.getHeight();

到

public void onDraw(Canvas canvas) {
    float canvasx = (float) getWidth();
    float canvasy = (float) getHeight();

但是，我不知道为什么更改解决了我的问题。

Answer 1

使用此：

float boardPosX = ((canvasx/2) - (bitmapx / 2));
float boardPosY = ((canvasy/2) - (bitmapy / 2));

Answer 2

private int mWidth;
private int mHeight;
private float mAngle;

@Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
    mWidth = View.MeasureSpec.getSize(widthMeasureSpec);
    mHeight = View.MeasureSpec.getSize(heightMeasureSpec);

    setMeasuredDimension(mWidth, mHeight);
}

@Override protected void onDraw(Canvas canvas)
{
    super.onDraw(canvas);
    Bitmap myBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.compass);

    // Here's the magic. Whatever way you do it, the logic is:
    // space available - bitmap size and divide the result by two.
    // There must be an equal amount of pixels on both sides of the image.
    // Therefore whatever space is left after displaying the image, half goes to
    // left/up and half to right/down. The available space you get by subtracting the
    // image's width/height from the screen dimensions. Good luck.

    int cx = (mWidth - myBitmap.getWidth()) >> 1; // same as (...) / 2
    int cy = (mHeight - myBitmap.getHeight()) >> 1;

    if (mAngle > 0) {
        canvas.rotate(mAngle, mWidth >> 1, mHeight >> 1);
    }

    canvas.drawBitmap(myBitmap, cx, cy, null);
}

Android drawBitmap位置参数

2 个答案: