学自定义View嘛，刚刚少些个重载构造函数，结果。。。

07-30 03:05:30.862 6924-6924/com.example.canvastest E/AndroidRuntime: FATAL EXCEPTION: mainProcess: com.example.canvastest, PID: 6924java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.canvastest/com.example.canvastest.SignalViewTest}: android.view.InflateException: Binary XML file line #10: Error inflating class com.example.canvastest.SignalLightViewat android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)at android.app.ActivityThread.access$800(ActivityThread.java:144)at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)at android.os.Handler.dispatchMessage(Handler.java:102)at android.os.Looper.loop(Looper.java:135)at android.app.ActivityThread.main(ActivityThread.java:5221)at java.lang.reflect.Method.invoke(Native Method)at java.lang.reflect.Method.invoke(Method.java:372)at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)Caused by: android.view.InflateException: Binary XML file line #10: Error inflating class com.example.canvastest.SignalLightViewat android.view.LayoutInflater.createView(LayoutInflater.java:616)at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:743)at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)at android.view.LayoutInflater.inflate(LayoutInflater.java:504)at android.view.LayoutInflater.inflate(LayoutInflater.java:414)at android.view.LayoutInflater.inflate(LayoutInflater.java:365)at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:292)at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)at com.example.canvastest.SignalViewTest.onCreate(SignalViewTest.java:13)at android.app.Activity.performCreate(Activity.java:5933)at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) Caused by: java.lang.NoSuchMethodException: <init> [class android.content.Context, interface android.util.AttributeSet]at java.lang.Class.getConstructor(Class.java:531)at java.lang.Class.getConstructor(Class.java:495)at android.view.LayoutInflater.createView(LayoutInflater.java:580)at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:743) at android.view.LayoutInflater.rInflate(LayoutInflater.java:806) at android.view.LayoutInflater.inflate(LayoutInflater.java:504) at android.view.LayoutInflater.inflate(LayoutInflater.java:414) at android.view.LayoutInflater.inflate(LayoutInflater.java:365) at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:292) at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) at com.example.canvastest.SignalViewTest.onCreate(SignalViewTest.java:13) at android.app.Activity.performCreate(Activity.java:5933) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
07-30 03:05:32.928 6924-6924/com.example.canvastest I/Process: Sending signal. PID: 6924 SIG: 9

’话不多说，上Demo代码：**

package com.example.canvastest;import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;/*** Created by 700 on 2018/7/30.*/public class SignalLightView extends View {private int count=0;public SignalLightView(Context context) {super(context);setFocusable(true);setFocusableInTouchMode(true);}@Overrideprotected void onDraw(Canvas canvas) {if(count<100){count++;}else{count=0;}Paint paint=new Paint();paint.setStrokeWidth(3.0f);switch(count%4){case 0:paint.setColor(Color.GREEN);break;case 1:paint.setColor(Color.RED);break;case 2:paint.setColor(Color.BLUE);break;case 3:paint.setColor(Color.YELLOW);break;default:paint.setColor(Color.WHITE);break;}canvas.drawCircle(80, 160, 50, paint);// 画圆，圆心的坐标(cx,cy)和半径radius}
}

NoSuchMethodException: <init> [class android.content.Context, interface android.util.AttributeSet].....
就是说自定义View的时候，三大领头重载构造函数要好好写好呐，缺了容易出错。
喏，三个补齐给他，就完事了：

public SignalLightView(Context context, AttributeSet attrs,int defStyleAttr) {super(context, attrs, defStyleAttr);setFocusable(true);setFocusableInTouchMode(true);}public SignalLightView(Context context, AttributeSet attrs) {super(context, attrs);setFocusable(true);setFocusableInTouchMode(true);}public SignalLightView(Context context) {super(context);setFocusable(true);setFocusableInTouchMode(true);}