Android TextView drawText BaseLine理解，设置内容垂直、水平居中

Android TextView drawText BaseLine理解 
 解决问题：如何设置绘制文本在盒子中 垂直居中
1. getHeight/2 设置为 drawText 绘制坐标，不能居中
  上代码XML:

Java代码：

package com.denganzhi.cusomerwidget.View;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;

/**
 * Created by Administrator on 2020/3/14.
 */

public class MyView extends View {
    public MyView(Context context) {
        super(context);
    }

    Paint paint=null;
    Context context;
    public MyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        this.context=context;
        //设置画笔
        paint=new Paint();
        paint.setColor(Color.BLACK);
        paint.setTextSize(80);
        paint.setTypeface(Typeface.DEFAULT_BOLD);  // 设置粗体
        paint.setAntiAlias(true);  // 消除锯齿

    }
    public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
    int pxW = dip2px(context,100);
    int pxH = dip2px(context,100);
    //pxW:200
    Log.e("denganzhi","pxW:"+pxW);
        // canvas 画板,背景色
        canvas.drawColor(Color.GREEN);
        Paint.FontMetrics fontMetrics = paint.getFontMetrics();
        // 这些坐标都是现对于baseLine的，top和ascent 是负数，在baseline的上面
        // bottom 、descent 是正数
       float top=fontMetrics.top;
       float bottom= fontMetrics.bottom;
       float asscent= fontMetrics.ascent;
       float descent=fontMetrics.descent;
       // top:-84.49219 bottom:21.679688 asscent:-74.21875descent:19.53125  Y100
        Log.e("denganzhi","top:"+top+" bottom:"+bottom+ " asscent:"+asscent+ "descent:"+descent +" centerY"+ getHeight()/2);
        // 画笔, 这个坐标是左下角的坐标，错误计算方法，baseLine 盒子 中心点，文字不能居中
          canvas.drawText("g我f",10,pxH/2,paint);
  // float newBaseLineY= getHeight()/2 + (( bottom-top)/2 - bottom);
   String drawStr="g我f";
   // X 轴居中
        //获取文本的宽度，和上面类似，但是是一个比较粗略的结果
        float measureText = paint.measureText(drawStr);
        Log.e("denganzhi1", "measureText="+measureText);
        // X 轴居中，盒子/2-文字宽度的/2 坐标开始绘制 文本
        float newBaseLineX = getWidth()/2 - measureText/2;
  // canvas.drawText(drawStr,newBaseLineX,newBaseLineY,paint);
    }

    public static int dip2px(Context context, float dpValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }
}

 文字未能垂直居中

分析： 文本绘制最坐标是getHeight()/2, baseline，文字在水平中心轴的上方,如果要实现文字水平居中，那么往下移动

 正确代码：

  float top=fontMetrics.top;
  float bottom= fontMetrics.bottom;
  float asscent= fontMetrics.ascent;
  float descent=fontMetrics.descent;
  float newBaseLineY= getHeight()/2 + (( bottom-top)/2 - bottom);

 float newBaseLineX = getWidth()/2 - measureText/2;
 

package com.denganzhi.cusomerwidget.View;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;

/**
 * Created by Administrator on 2020/3/14.
 */

public class MyView extends View {
    public MyView(Context context) {
        super(context);
    }

    Paint paint=null;
    Context context;
    public MyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        this.context=context;
        //设置画笔
        paint=new Paint();
        paint.setColor(Color.BLACK);
        paint.setTextSize(80);
        paint.setTypeface(Typeface.DEFAULT_BOLD);  // 设置粗体
        paint.setAntiAlias(true);  // 消除锯齿

    }
    public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
    int pxW = dip2px(context,100);
    int pxH = dip2px(context,100);
    //pxW:200
    Log.e("denganzhi","pxW:"+pxW);
        // canvas 画板,背景色
        canvas.drawColor(Color.GREEN);
        Paint.FontMetrics fontMetrics = paint.getFontMetrics();
        // 这些坐标都是现对于baseLine的，top和ascent 是负数，在baseline的上面
        // bottom 、descent 是正数
       float top=fontMetrics.top;
       float bottom= fontMetrics.bottom;
       float asscent= fontMetrics.ascent;
       float descent=fontMetrics.descent;
       // top:-84.49219 bottom:21.679688 asscent:-74.21875descent:19.53125  Y100
        Log.e("denganzhi","top:"+top+" bottom:"+bottom+ " asscent:"+asscent+ "descent:"+descent +" centerY"+ getHeight()/2);
        // 画笔, 这个坐标是左下角的坐标，错误计算方法，baseLine 盒子 中心点，文字不能居中
      //    canvas.drawText("g我f",10,pxH/2,paint);
   float newBaseLineY= getHeight()/2 + (( bottom-top)/2 - bottom);
   String drawStr="g我f";
   // X 轴居中
        //获取文本的宽度，和上面类似，但是是一个比较粗略的结果
        float measureText = paint.measureText(drawStr);
        Log.e("denganzhi1", "measureText="+measureText);
        // X 轴居中，盒子/2-文字宽度的/2 坐标开始绘制 文本
        float newBaseLineX = getWidth()/2 - measureText/2;
   canvas.drawText(drawStr,newBaseLineX,newBaseLineY,paint);
    }

    public static int dip2px(Context context, float dpValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }
}

输出效果：

pxW:200
top:-84.49219 bottom:21.679688 asscent:-74.21875descent:19.53125 centerY100
measureText=155.0

运行效果：

效果分析：