项目轮子：波浪背景

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⚙️项目轮子：波浪背景

前言：使用自定义view+view函数的绘制相关知识，来建一个项目轮子，以供以后使用

💅对于自定义view比较熟悉的话就会很容易写出来，难的是view函数的绘制（实现波浪的效果)

1.基类

package com.example.android_wavebackground;
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PaintFlagsDrawFilter;
import android.os.Build;
import android.util.AttributeSet;
import android.widget.RelativeLayout;import androidx.annotation.RequiresApi;public class BgRelativeLayout extends RelativeLayout {private PaintFlagsDrawFilter mDrawFilter;private Paint mWavePaint;//三角函数的初象private float mOffset1 = 0.0f;private float mOffset2 = 0.0f;private float mSpeed1 = 0.05f;private float mSpeed2 = 0.07f;@RequiresApi(api = Build.VERSION_CODES.M)public BgRelativeLayout(Context context) {this(context,null);}@RequiresApi(api = Build.VERSION_CODES.M)public BgRelativeLayout(Context context, AttributeSet attrs) {this(context, attrs,0);}@RequiresApi(api = Build.VERSION_CODES.M)public BgRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);initView();}@RequiresApi(api = Build.VERSION_CODES.M)@SuppressLint("ResourceAsColor")private void initView() {// 初始绘制波纹的画笔mWavePaint = new Paint();// 去除画笔锯齿mWavePaint.setAntiAlias(true);// 设置风格为实线mWavePaint.setStyle(Paint.Style.FILL);// 设置画笔颜色mWavePaint.setColor(getResources().getColor(R.color.design_default_color_primary_dark,null));mDrawFilter = new PaintFlagsDrawFilter(0, Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG);}@Overrideprotected void dispatchDraw(Canvas canvas) {initDrawBg(canvas);//放在super前是后景，相反是前景，前景会覆盖子布局super.dispatchDraw(canvas);}private void initDrawBg(Canvas canvas) {// 从canvas层面去除绘制时锯齿canvas.setDrawFilter(mDrawFilter);for (int i = 0; i < getWidth(); i++) {// y = A * sin( wx + b) + h ; A： 浪高； w：周期；b：初相；  h: y轴的偏移位置float endY = (float) (20 * Math.sin(2 * Math.PI / getWidth() * i + mOffset1) + 330);//h:是y轴方向的偏移量//startY: 0就是从最顶部开始//画第一条波浪canvas.drawLine(i, 0, i, endY, mWavePaint);//跟第一条线一样float endY2 = (float) (20 * Math.sin(2 * Math.PI / getWidth() * i + mOffset2) + 330);//画第二条波浪canvas.drawLine(i, 0, i, endY2, mWavePaint);}if (mOffset1 > Float.MAX_VALUE - 1) {//防止数值超过浮点型的最大值mOffset1 = 0;}mOffset1 += mSpeed1;if (mOffset2 > Float.MAX_VALUE - 1) {//防止数值超过浮点型的最大值mOffset2 = 0;}mOffset2 += mSpeed2;//刷新postInvalidate();}}

代码注释已经很详细了，在此不多做解释

2.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MainActivity"><com.example.android_wavebackground.BgRelativeLayoutandroid:layout_height="250dp"android:layout_width="match_parent"android:background="#1878FF"/><!--放子view--></LinearLayout>