java.lang.NullPointerException、field ‘’ is never assigned

1.刚刚写好一个Demo：

package com.example.canvastest; import android.content.Context; import android.graphics.Canvas; import android.graphics.Paint; import android.util.AttributeSet; import android.view.View; /** * Created by 700 on 2018/7/30. */ public class DrawRectView extends View{ //1/4 定义变量 private Paint mRectPaintStroke; private Paint mRectPaintFill; private int[] rect1 = new int[]{10, 10 , 110, 110}; private int[] rect2 = new int[]{10, 310 , 110, 410}; //2/4 三个构造函数 public DrawRectView(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); } public DrawRectView(Context context, AttributeSet attrs) { super(context, attrs); } public DrawRectView(Context context) { super(context); } //3/4 初始化画笔 private void initView(){ mRectPaintFill.setColor(getResources().getColor( android.R.color.holo_blue_bright)); mRectPaintFill.setStyle(Paint.Style.FILL); mRectPaintStroke.setColor(getResources().getColor( android.R.color.holo_blue_bright)); mRectPaintStroke.setStyle(Paint.Style.STROKE); } //4/4 开画 @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawRect(rect1[0],rect1[1],rect1[2],rect1[3],mRectPaintStroke); canvas.drawRect(rect2[0],rect2[1],rect2[2],rect2[3],mRectPaintFill); } } 

2.一运行：

07-29 14:34:45.660 4468-4468/com.example.canvastest E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.canvastest, PID: 4468 java.lang.NullPointerException: Attempt to read from field 'long android.graphics.Paint.mNativePaint' on a null object reference at android.view.GLES20Canvas.drawRect(GLES20Canvas.java:843) at com.example.canvastest.DrawRectView.onDraw(DrawRectView.java:50) at android.view.View.draw(View.java:15114) at android.view.View.updateDisplayListIfDirty(View.java:14048) at android.view.View.getDisplayList(View.java:14071) at android.view.View.draw(View.java:14838) at android.view.ViewGroup.drawChild(ViewGroup.java:3404) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198) at android.view.View.updateDisplayListIfDirty(View.java:14043) at android.view.View.getDisplayList(View.java:14071) at android.view.View.draw(View.java:14838) at android.view.ViewGroup.drawChild(ViewGroup.java:3404) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198) at android.view.View.updateDisplayListIfDirty(View.java:14043) at android.view.View.getDisplayList(View.java:14071) at android.view.View.draw(View.java:14838) at android.view.ViewGroup.drawChild(ViewGroup.java:3404) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198) at android.view.View.updateDisplayListIfDirty(View.java:14043) at android.view.View.getDisplayList(View.java:14071) at android.view.View.draw(View.java:14838) at android.view.ViewGroup.drawChild(ViewGroup.java:3404) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3198) at android.view.View.draw(View.java:15117) at android.widget.FrameLayout.draw(FrameLayout.java:592) at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2595) at android.view.View.updateDisplayListIfDirty(View.java:14048) at android.view.View.getDisplayList(View.java:14071) at android.view.ThreadedRenderer.updateViewTreeDisplayList(ThreadedRenderer.java:266) at android.view.ThreadedRenderer.updateRootDisplayList(ThreadedRenderer.java:272) at android.view.ThreadedRenderer.draw(ThreadedRenderer.java:311) at android.view.ViewRootImpl.draw(ViewRootImpl.java:2492) at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2337) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1968) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) at android.view.Choreographer.doCallbacks(Choreographer.java:580) at android.view.Choreographer.doFrame(Choreographer.java:550) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) 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) 07-29 14:34:47.589 4468-4468/com.example.canvastest I/Process: Sending signal. PID: 4468 SIG: 9 

3.呵呵哒，看了一下，发现就是写好了忘记调用 initView()了 ←_←。。。
好的加在onDraw()里面，再来。。。。

有没有搞错啊。。。
又看了一下。。。好的。。。

几个意思捏，就是缩声明了变量之后，没给它new一下啊 ←_←。。。
好的，在onDraw里面给你new了，可以了吧。。。可以了

真是饶人的小妖精，新车上路，注意系好安全带

那个，就是在学绘图机制，过阵子写个简书总结一下昂