canvse的save和restore方法总结

概要：

save：用来保存Canvas的状态。save之后，可以调用Canvas的平移、放缩、旋转、错切、裁剪等操作。

restore：用来恢复Canvas之前保存的状态。防止save后对Canvas执行的操作对后续的绘制有影响。

save和restore要配对使用（restore可以比save少，但不能多），如果restore调用次数比save多，会引发Error

直接上代码和截图，看代码注释

package com.example.drawtest;

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 MyTextView extends View {

    public MyTextView(Context context) {
        super(context);
    }

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

    public MyTextView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint bluePaint = getPaint(Color.BLUE, Paint.Style.FILL);
        Paint redPaint = getPaint(Color.RED, Paint.Style.FILL);
        Paint whitePaint = getPaint(Color.WHITE, Paint.Style.FILL);
        Paint cyanPaint = getPaint(Color.CYAN, Paint.Style.STROKE);
        Paint blackPaint = getPaint(Color.BLACK, Paint.Style.STROKE);

        //绘制蓝色底图和一个红色圆圈
        draw(canvas, bluePaint, redPaint);
        //保存当前状态
        canvas.save();
        //顺时针旋转15度
        canvas.rotate(15);
        //在旋转后的画布上绘制一个黑色矩形边框和红色圆圈
        draw(canvas, blackPaint, redPaint);
        //再进行缩放一半操作
        canvas.scale(0.5f, 0.5f);
        //绘制一个浅蓝色边框和红色圆圈后将图像缩放一半
        draw(canvas, cyanPaint, redPaint);
        //恢复之前保存的状态
        canvas.restore();
        //在之前的画布上继续绘制一个白色圆圈,相对前一个圆圈右移
        canvas.drawCircle(getMeasuredWidth() * 8 / 10, 20, 20, whitePaint);
    }

    /**
     * @param canvas      画布
     * @param rectPaint   矩形用到的画笔
     * @param circlePaint 圆形用到的画笔
     */
    private void draw(Canvas canvas, Paint rectPaint, Paint circlePaint) {
        canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), rectPaint);
        canvas.drawCircle(getMeasuredWidth() * 7 / 10, 20, 20, circlePaint);
    }

    /**
     * 获取画笔
     *
     * @param color 画笔颜色
     * @param style 画笔风格
     * @return 画笔
     */
    public Paint getPaint(int color, Paint.Style style) {
        Paint paint = new Paint();
        paint.setStrokeWidth(20);
        paint.setAntiAlias(true);
        paint.setStyle(style);
        paint.setColor(color);
        return paint;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.drawtest.MainActivity">

    <com.example.drawtest.MyTextView
        android:layout_width="300dp"
        android:layout_height="500dp"
        android:layout_centerInParent="true"/>
</RelativeLayout>

运行效果图

其实他的实现逻辑，如下图所示

注意点：移动或者旋转后，坐标仍然是按照之前的坐标来计算