Android 使用Kotlin自定义View的方法教程

前言

随着google宣布kotlin作为官方开发语言，在Android中使用kotlin的趋势也越来越明显，最近被kotlin的文章轰炸了，所以决定上手试一下，试过之后，感觉靠它灵简直有魔性。特别是一句话写出一个复杂的循环的时候，简直被惊呆。而且使用AS，Java代码可以直接转成Kotlin。

效果图如下：

首先是这次自定义View的效果图，是一张饼图。如果是用java写的话也就几十行，觉得换成Kotlin的话可能会更少。

示例代码

主要的功能是可以任设定数据的个数，我这里是4个数据，可以任意设定每个数据的颜色。

#####首先上Kotlin代码#####

package top.greendami.mykotlinapp
import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.view.View
/**
 * Created by GreendaMi on 2017/4/10.
 */
class PPCircle : View {
 var mDatas = ArrayList<Float>()
 var mColors = ArrayList<Int>(4)
 var mPaint: Paint = Paint()
 constructor(mContext: Context) : super(mContext) {
 val context = mContext
 }
 constructor(mContext: Context, mAttributeSet: AttributeSet) : super(mContext, mAttributeSet) {
 initPaint()
 val context = mContext
 }
 fun initPaint() {
 mPaint.isAntiAlias = true
 mPaint.style = Paint.Style.FILL_AND_STROKE
 mPaint.color = 0xff44b391.toInt()
 }
 //长宽一致
 override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
 super.onMeasure(widthMeasureSpec, heightMeasureSpec)
 val widthSpecSize = View.MeasureSpec.getSize(widthMeasureSpec)
 val heightSpecSize = View.MeasureSpec.getSize(heightMeasureSpec)
 val mLayoutSize = Math.min(widthSpecSize, heightSpecSize)
 setMeasuredDimension(mLayoutSize, mLayoutSize)
 }
 /**
 * 设置数据
 */
 fun setData(data: ArrayList<Float>, colors: ArrayList<Int>) {
 mDatas = data
 mColors = colors
 invalidate()
 }
 override fun onDraw(canvas: Canvas?) {
 super.onDraw(canvas)
 if (mDatas.size == 0) {
  return
 }
 //切掉圆心
 var mPath = Path()
 mPath.addCircle(width / 2f, height / 2f, width / 2f * 0.4f,Path.Direction.CW)
 mPath.close()
 canvas?.clipPath(mPath, Region.Op.XOR)
 var total = 0f
 //此处亮点
 mDatas.forEach { total += it }
 var rf = RectF(0f, 0f, width.toFloat(), height.toFloat())
 var startAngle = -90f//起点
 var i = 0
 mDatas.forEach {
  mPaint.color = mColors[i]
  var sweepAngle = it * 360 / total
  canvas?.drawArc(rf, startAngle, sweepAngle, true, mPaint)
  startAngle += sweepAngle
  i++
 }
 }
}

设置数据

package top.greendami.mykotlinapp
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main2.*
class Main2Activity : AppCompatActivity() {
 override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  setContentView(R.layout.activity_main2)
  var mDatas = ArrayList<Float>()
  mDatas.add(1f)
  mDatas.add(2f)
  mDatas.add(4f)
  mDatas.add(2f)
  var mColors = ArrayList<Int>()
  mColors.add(0xff83ccd2.toInt())
  mColors.add(0xffc0e1ce.toInt())
  mColors.add(0xfffac55e.toInt())
  mColors.add(0xffef805f.toInt())
  ppCircle.setData(mDatas,mColors)
 }
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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="top.greendami.mykotlinapp.Main2Activity">
 <top.greendami.mykotlinapp.PPCircle
  android:id="@+id/ppCircle"
  android:layout_width="300dp"
  android:layout_height="300dp"  app:layout_constraintBottom_toBottomOf="parent"
  android:layout_marginBottom="8dp"
  android:layout_marginRight="8dp"
  app:layout_constraintRight_toRightOf="parent"
  app:layout_constraintTop_toTopOf="parent"
  android:layout_marginTop="8dp"
  android:layout_marginLeft="8dp"
  app:layout_constraintLeft_toLeftOf="parent" />
</android.support.constraint.ConstraintLayout>

#####相同功能Java代码#####

package com.allrun.arsmartelevatorformanager.widget;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RectF;
import android.graphics.Region;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.View;
import java.util.ArrayList;
import java.util.List;
/**
 * Created by GreendaMi on 2017/4/11.
 */
public class PPCircle extends View {
 Context mContext;
 List<Float> mData = new ArrayList<Float>();//数据
 List<Integer> mColors = new ArrayList<Integer>();//数据对应的颜色
 Paint mPaint = new Paint();
 public PPCircle(Context context) {
  super(context);
 }
 public PPCircle(Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);
  mContext = context;
  initPaint();
 }
 private void initPaint() {
  mPaint.setAntiAlias(true);
  mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
 }
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  int widthSpecSize = View.MeasureSpec.getSize(widthMeasureSpec);
  int heightSpecSize = View.MeasureSpec.getSize(heightMeasureSpec);
  int mLayoutSize = Math.min(widthSpecSize, heightSpecSize);
  setMeasuredDimension(mLayoutSize, mLayoutSize);
 }
 public void setData(List<Float> mData, List<Integer> mColors) {
  this.mData = mData;
  this.mColors = mColors;
 }
 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  if (mData.size() == 0) {
   return;
  }
  //切掉圆心
  Path mPath =new Path();
  mPath.addCircle(getWidth()/2,getWidth()/2,getWidth()/2* 0.4f ,Path.Direction.CW);
  canvas.clipPath(mPath, Region.Op.XOR);

  float total = 0;
  for(float temp : mData){
   total = total + temp;
  }
  RectF rf = new RectF(0f, 0f, getWidth(), getHeight());
  float startAngle = -90f;//起点
  int i = 0;
  for(float temp : mData){
   mPaint.setColor(mColors.get(i));
   float sweepAngle = temp * 360 / total;
   canvas.drawArc(rf, startAngle, sweepAngle, true, mPaint);
   startAngle += sweepAngle;
   i++;
  }
 }
}

说说Kotlin和Java感觉差异比较大的地方。首先是变量的生命，Kotlin声明时必须赋值或者初始化，java则不用，开始有点不习惯。Kotlin不需要分号结尾，Kotlin的循环用起来简直爽YY。

总结

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