Android开发-自定义View-AndroidStudio(二十二)FontMetrics计算文字居中

package com.iwanghang.newview;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getSupportActionBar().hide();
        //setContentView(R.layout.activity_main);
        NewView newView = new NewView(this);
        setContentView(newView);
    }
}

package com.iwanghang.newview;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class NewView extends View{
    // 单元格的宽度和高度
    private float width;
    private float height;

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

    public NewView(MainActivity mainActivity) {
        super(mainActivity);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        this.width = w / 9f;
        this.height = h / 9f;
        super.onSizeChanged(w, h, oldw, oldh);
    }

    // 当Android系统需要绘制一个View对象时，就会调用该对象的onDraw
    @Override
    protected void onDraw(Canvas canvas) {
        // 画背景
        Paint backgroundPaint = new Paint();
        backgroundPaint.setColor(getResources().getColor(R.color.colorBackground));
        canvas.drawRect(0,0,getWidth(),getHeight(),backgroundPaint);

        Paint darkPaint = new Paint();
        darkPaint.setColor(getResources().getColor(R.color.colorDark));

        Paint hilitePaint = new Paint();
        hilitePaint.setColor(getResources().getColor(R.color.colorHilite));

        Paint lightPaint = new Paint();
        lightPaint.setColor(getResources().getColor(R.color.colorLight));

        // 绘制9X9的网络格
        // 两条距离为1的直线，视觉上会有割裂的效果
        for (int i = 0; i < 9; i++) {
            canvas.drawLine(0, i*height, getWidth(), i*height, lightPaint);
            canvas.drawLine(0, i*height+1, getWidth(), i*height+1, hilitePaint);
            canvas.drawLine(i*width, 0, i*width, getHeight(), lightPaint);
            canvas.drawLine(i*width+1, 0, i*width+1, getHeight(), hilitePaint);
        }

        // 绘制3X3的网络格
        for (int i = 0; i < 9; i++) {
            if (i % 3 != 0) {
                continue;
            }
            canvas.drawLine(0, i*height, getWidth(), i*height, darkPaint);
            canvas.drawLine(0, i*height+1, getWidth(), i*height+1, hilitePaint);
            canvas.drawLine(i*width, 0, i*width, getHeight(), darkPaint);
            canvas.drawLine(i*width+1, 0, i*width+1, getHeight(), hilitePaint);
        }

        // 绘制数字
        Paint numberPaint = new Paint();
        numberPaint.setColor(Color.BLACK);
        numberPaint.setStyle(Paint.Style.STROKE);
        numberPaint.setTextSize(height*0.75f);
        numberPaint.setTextAlign(Paint.Align.CENTER);
        numberPaint.setAntiAlias(true); // 抗锯齿

        /**
         * 数字居中位置
         * x轴居中比较容易计算
         * y轴居中的计算，依赖于FontMetrics，大家很容易百度到相关的知识
         */
        Paint.FontMetrics fm = numberPaint.getFontMetrics();
        float x = width / 2;
        float y = height / 2 - (fm.ascent + fm.descent) / 2;

        canvas.drawText("1", 0 * width + x, 0 * height + y, numberPaint);
        canvas.drawText("2", 1 * width + x, 1 * height + y, numberPaint);
        canvas.drawText("3", 2 * width + x, 2 * height + y, numberPaint);
        canvas.drawText("4", 3 * width + x, 3 * height + y, numberPaint);
        canvas.drawText("5", 4 * width + x, 4 * height + y, numberPaint);

        super.onDraw(canvas);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="colorPrimary">#3F51B5</color>
    <color name="colorPrimaryDark">#303F9F</color>
    <color name="colorAccent">#FF4081</color>

    <color name="colorHilite">#ffffff</color>
    <color name="colorLight">#64c6d4ef</color>
    <color name="colorDark">#6456648f</color>
    <color name="colorBackground">#ffe6f0ff</color>
</resources>

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