如何解决NullPointerException in android.view.GLES20RecordingCanvas

一、如何解决NullPointerException in android.view.GLES20RecordingCanvas

在发布版本的最后一轮过设备时，在某老旧设备上出现了空指针异常

java.lang.NullPointerException
at android.view.GLES20RecordingCanvas.drawPatch(GLES20RecordingCanvas.java:97)
at android.graphics.NinePatch.draw(NinePatch.java:125)
at android.graphics.drawable.NinePatchDrawable.draw(NinePatchDrawable.java:189)
at android.widget.ScrollBarDrawable.drawThumb(ScrollBarDrawable.java:178)
at android.widget.ScrollBarDrawable.draw(ScrollBarDrawable.java:137)
at android.view.View.onDrawVerticalScrollBar(View.java:9532)
at android.view.View.onDrawScrollBars(View.java:9476)
at android.view.View.draw(View.java:11091)
at android.widget.AbsListView.draw(AbsListView.java:3428)
at android.view.View.getDisplayList(View.java:10455)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.ViewGroup.drawChild(ViewGroup.java:2858)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2497)
at android.view.View.draw(View.java:11067)
at android.view.View.getDisplayList(View.java:10455)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.ViewGroup.dispatchGetDisplayList(ViewGroup.java:2605)
at android.view.View.getDisplayList(View.java:10418)
at android.view.HardwareRenderer$GlRenderer.draw(HardwareRenderer.java:879)
at android.view.ViewRootImpl.draw(ViewRootImpl.java:1955)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1661)
at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2505)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:4945)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)

开始出现闪退时觉得很惊讶，抓了日志马上谷歌。发现原来是android 4.0.X对不支持.9图片硬件加速，而从android4.0.x（SDK 14）开始系统默认打开硬件加速。

解决方法：view取消硬件加速

myView.setLayerType(View.LAYER_TYPE_SOFTWARE, null);

二、扩展阅读

在自定义控件或者自定义绘画时，应该注意使用的api是否支持硬件加速，以避免出现闪退情况

First supported API level

Canvas

drawBitmapMesh() (colors array)

18

drawPicture()

23

drawPosText()

16

drawTextOnPath()

16

drawVertices()

✗

setDrawFilter()

16

clipPath()

18

clipRegion()

18

clipRect(Region.Op.XOR)

18

clipRect(Region.Op.Difference)

18

clipRect(Region.Op.ReverseDifference)

18

clipRect() with rotation/perspective

18

Paint

setAntiAlias() (for text)

18

setAntiAlias() (for lines)

16

setFilterBitmap()

17

setLinearText()

✗

setMaskFilter()

✗

setPathEffect() (for lines)

✗

setRasterizer()

✗

setShadowLayer() (other than text)

✗

setStrokeCap() (for lines)

18

setStrokeCap() (for points)

19

setSubpixelText()

✗

Xfermode

PorterDuff.Mode.DARKEN (framebuffer)

✗

PorterDuff.Mode.LIGHTEN (framebuffer)

✗

PorterDuff.Mode.OVERLAY (framebuffer)

✗

Shader

ComposeShader inside ComposeShader

✗

Same type shaders inside ComposeShader

✗

Local matrix on ComposeShader

18

画布Canvas的scale方法

Drawing operation to be scaled	First supported API level
drawText()	18
drawPosText()	✗
drawTextOnPath()	✗
Simple Shapes*	17
Complex Shapes*	✗
drawPath()	✗
Shadow layer	✗

关注最新api请移步官网链接

https://developer.android.com/guide/topics/graphics/hardware-accel.html

参考文章： https://stackoverflow.com/questions/18340296/nullpointerexception-in-android-view-gles20recordingcanvas

说明：因为实际的错误堆栈会知道本人开发的实际项目，所以本博客的错误堆栈使用StackoverFlow问题中的内容。