Android之drawText()文字居中问题

Android之drawText()文字居中问题

问题来自于HenCoder 的 这篇博客练习中的Practice13GetTextBoundsView，关于让文字居中绘制的问题。

首先以矩形的中心那条线为baseLine绘制文字，

        int middle = (top + bottom) / 2;   // 矩形中心的高度坐标         canvas.drawText(texts[0], 100, middle, paint2);        canvas.drawText(texts[1], 200, middle, paint2);        canvas.drawText(texts[2], 300, middle, paint2);        canvas.drawText(texts[3], 400, middle, paint2);        canvas.drawText(texts[4], 500, middle, paint2);        canvas.drawText(texts[5], 600, middle, paint2);

结果如下图（下面那个）

按照我们的理解（想当然），要使文字居中，则需要把上述绘制文字的y值要下平移每个字母的高度一半即可。

代码

        int middle = (top + bottom) / 2;        paint2.getTextBounds(text1,0,text1.length(), textRect);        int middle1 = middle+ (textRect.bottom-textRect.top)/2;        canvas.drawText(text1, 100, middle1, paint2);        paint2.getTextBounds(text2,0,text2.length(), textRect);        int middle2 = middle+ (textRect.bottom-textRect.top)/2;        canvas.drawText(text2, 200, middle2, paint2);        paint2.getTextBounds(text3,0,text3.length(), textRect);        int middle3 = middle+ (textRect.bottom-textRect.top)/2;        canvas.drawText(text3, 300, middle3, paint2);        paint2.getTextBounds(text4,0,text4.length(), textRect);        int middle4 = middle+ (textRect.bottom-textRect.top)/2;        canvas.drawText(text4, 400, middle4, paint2);        paint2.getTextBounds(text5,0,text5.length(), textRect);        int middle5 = middle+ (textRect.bottom-textRect.top)/2;        canvas.drawText(text5, 500, middle5, paint2);        paint2.getTextBounds(text6,0,text6.length(), textRect);        int middle6 = middle+ (textRect.bottom-textRect.top)/2;        canvas.drawText(text6, 600, middle6, paint2);

然而并结果不是我们想的那样

这样看上去，别的字符都正常，唯独那个 j 出了问题。

于是把每个文字对应的textBound 的 top、 bottom 都打出来

 yOffsets[0]     top= -114      bottom=   0 yOffsets[1]     top= -87       bottom=   2 yOffsets[2]     top= -114      bottom=   2 yOffsets[3]     top= -116      bottom=   35 yOffsets[4]     top= -144      bottom=   0 yOffsets[5]     top= -120      bottom=   2

其实 paint.getTextBounds（）得到是包含文字的最小矩形，其默认就是以（0，0）为基线来测量文字的，插个图

即默认的下面那条baseline为（0,0）那条线，则 最小矩形 middle 的 y值为

middle  =  (bounds.top + bounds.bottom)/2;   // 为负数

baseline = middle+ (baseline和middle之间的间距);

所以要使文字居中，则具体每个文字的baseline为

      int middle = (top + bottom) / 2;      int baseline = (int) (middle -(textBound .top+ textBound .bottom) / 2);

修正之后的代码

int middle = (top + bottom) / 2;paint2.getTextBounds(texts[0], 0, texts[0].length(), textBounds);yOffsets[0] = - (textBounds.top + textBounds.bottom) / 2;   //即上述baseline和middle之间的间距paint2.getTextBounds(texts[1], 0, texts[1].length(), textBounds);yOffsets[1] = - (textBounds.top + textBounds.bottom) / 2;paint2.getTextBounds(texts[2], 0, texts[2].length(), textBounds);yOffsets[2] = - (textBounds.top + textBounds.bottom) / 2;paint2.getTextBounds(texts[3], 0, texts[3].length(), textBounds);yOffsets[3] = - (textBounds.top + textBounds.bottom) / 2;paint2.getTextBounds(texts[4], 0, texts[4].length(), textBounds);yOffsets[4] = - (textBounds.top + textBounds.bottom) / 2;paint2.getTextBounds(texts[5], 0, texts[5].length(), textBounds);yOffsets[5] = - (textBounds.top + textBounds.bottom) / 2;canvas.drawText(texts[0], 100, middle + yOffsets[0], paint2);canvas.drawText(texts[1], 200, middle + yOffsets[1], paint2);canvas.drawText(texts[2], 300, middle + yOffsets[2], paint2);canvas.drawText(texts[3], 400, middle + yOffsets[3], paint2);canvas.drawText(texts[4], 500, middle + yOffsets[4], paint2);canvas.drawText(texts[5], 600, middle + yOffsets[5], paint2);

最终结果