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

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老规矩，先上图，看个效果，如果符合你的项目或者确定你要了解的内容，再往下看吧：
先了解一下FontMetrics，然后再看看Demo：





MainActivity.java：

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);    }}

NewView.java：

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);    }}

colors.xml：

<?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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