[移动开发]一次RadialGradient导致的崩溃的原因定位

背景是我们的应用在android5.0的机器上会崩溃

崩溃堆栈如下：

java.lang.IllegalArgumentException: radius must be > 0
	at android.graphics.RadialGradient.<init>(RadialGradient.java:57)
	at android.graphics.drawable.GradientDrawable.ensureValidRect(GradientDrawable.java:938)
	at android.graphics.drawable.GradientDrawable.draw(GradientDrawable.java:509)
	at android.graphics.drawable.LayerDrawable.draw(LayerDrawable.java:537)
	at android.view.View.getDrawableRenderNode(View.java:15396)
	at android.view.View.drawBackground(View.java:15347)
	at android.view.View.draw(View.java:15113)
	at android.widget.FrameLayout.draw(FrameLayout.java:592)
	at android.view.View.updateDisplayListIfDirty(View.java:14056)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.view.View.draw(View.java:15125)
	at android.widget.FrameLayout.draw(FrameLayout.java:592)
	at android.view.View.updateDisplayListIfDirty(View.java:14056)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.view.View.draw(View.java:15125)
	at android.widget.FrameLayout.draw(FrameLayout.java:592)
	at android.view.View.updateDisplayListIfDirty(View.java:14056)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.support.constraint.ConstraintLayout.dispatchDraw()
	at android.view.View.draw(View.java:15125)
	at android.view.View.updateDisplayListIfDirty(View.java:14056)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.view.View.updateDisplayListIfDirty(View.java:14051)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.view.View.updateDisplayListIfDirty(View.java:14051)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.view.View.updateDisplayListIfDirty(View.java:14051)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.view.View.updateDisplayListIfDirty(View.java:14051)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.View.draw(View.java:14846)
	at android.view.ViewGroup.drawChild(ViewGroup.java:3405)
	at android.view.ViewGroup.dispatchDraw(ViewGroup.java:3199)
	at android.view.View.draw(View.java:15125)
	at android.widget.FrameLayout.draw(FrameLayout.java:592)
	at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2713)
	at android.view.View.updateDisplayListIfDirty(View.java:14056)
	at android.view.View.getDisplayList(View.java:14079)
	at android.view.ThreadedRenderer.updateViewTreeDisplayList(ThreadedRenderer.java:266)
	at android.view.ThreadedRenderer.updateRootDisplayList(ThreadedRenderer.java:272)
	at android.view.ThreadedRenderer.draw(ThreadedRenderer.java:311)
	at android.view.ViewRootImpl.draw(ViewRootImpl.java:2532)
	at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2370)
	at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2001)
	at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1079)
	at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5839)
	at android.view.Choreographer$CallbackRecord.run(Choreographer.java:836)
	at android.view.Choreographer.doCallbacks(Choreographer.java:635)
	at android.view.Choreographer.doFrame(Choreographer.java:601)
	at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:822)
	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:5318)
	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:922)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:717)

其他已知信息

只有5.0的机器才会崩溃，5.1+之后的设备都不会崩溃，这个版本的代码中新增加了一个背景，用xml写的，细节如下

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="oval">
            <gradient
                android:endColor="@android:color/black"
                android:gradientRadius="100%"
                android:startColor="@android:color/red"
                android:type="radial" />
        </shape>
    </item>
</layer-list>

解决方法

删了背景重新上线。

绕过方法

方法一：把100%换成100%p

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="oval">
            <gradient
                android:endColor="@android:color/black"
                android:gradientRadius="100%p"
                android:startColor="@android:color/red"
                android:type="radial" />
        </shape>
    </item>
</layer-list>

方法二：增加width、height

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="oval">
            <gradient
                android:endColor="@android:color/black"
                android:gradientRadius="100%"
                android:startColor="@android:color/red"
                android:width="100dp"
                android:height="100dp"
                android:type="radial" />
        </shape>
    </item>
</layer-list>

原因

相关代码在 5.0.0-GradientDrawable 、 5.1.0-GradientDrawable

代码区别点：

5.0

919   float radius = st.mGradientRadius;
920   if (st.mGradientRadiusType == RADIUS_TYPE_FRACTION) {
921        radius *= Math.min(st.mWidth, st.mHeight);
922   } else if (st.mGradientRadiusType == RADIUS_TYPE_FRACTION_PARENT) {
923        radius *= Math.min(r.width(), r.height());
924   }
925
926   if (st.mUseLevel) {
927        radius *= getLevel() / 10000.0f;
928   }
929
930   mGradientRadius = radius;
931
932   if (radius == 0) {
933       // We can't have a shader with zero radius, so let's
934       // have a very, very small radius.
935       radius = 0.001f;
936   }
937
938   mFillPaint.setShader(new RadialGradient(
939       x0, y0, radius, colors, null, Shader.TileMode.CLAMP));

5.1

961 if (radius <= 0) {
962    // We can't have a shader with non-positive radius, so
963    // let's have a very, very small radius.
964    radius = 0.001f;
965 }
966
967 mFillPaint.setShader(new RadialGradient(
968    x0, y0, radius, colors, null, Shader.TileMode.CLAMP));

分析

1. 100%走到这个分支判断（mGradientRadiusType ==RADIUS_TYPE_FRACTION)中，这时候的st.mWidth为-1，所以radius乘出来是负数，if (radius == 0)拦不住，所以new RadialGradient的时候抛出了异常。
2. 5.1的代码，修改了if (radius <= 0)，所以拦住了崩溃。
3. 这种场景下，使用100%p，就会走到下面的分支(st.mGradientRadiusType == RADIUS_TYPE_FRACTION_PARENT) ，这个分支中r.width()不是-1，所以能正常使用不会崩溃。
4. 除了换成%p，另外一种解法应该也可以，就是为gradient设置width、height。
5. 在这个点上，应该理解为：%p是基于父布局的百分比布局，%是基于自身的百分比布局。

其他的一些背景知识

除了%，%p，android中还支持在xml中使用如下单位，他们的含义如下：

参考-androidfw/ResourceTypes

4363 static const unit_entry unitNames[] = {
4364    { "px", strlen("px"), Res_value::TYPE_DIMENSION, Res_value::COMPLEX_UNIT_PX, 1.0f },
4365    { "dip", strlen("dip"), Res_value::TYPE_DIMENSION, Res_value::COMPLEX_UNIT_DIP, 1.0f },
4366    { "dp", strlen("dp"), Res_value::TYPE_DIMENSION, Res_value::COMPLEX_UNIT_DIP, 1.0f },
4367    { "sp", strlen("sp"), Res_value::TYPE_DIMENSION, Res_value::COMPLEX_UNIT_SP, 1.0f },
4368    { "pt", strlen("pt"), Res_value::TYPE_DIMENSION, Res_value::COMPLEX_UNIT_PT, 1.0f },
4369    { "in", strlen("in"), Res_value::TYPE_DIMENSION, Res_value::COMPLEX_UNIT_IN, 1.0f },
4370    { "mm", strlen("mm"), Res_value::TYPE_DIMENSION, Res_value::COMPLEX_UNIT_MM, 1.0f },
4371    { "%", strlen("%"), Res_value::TYPE_FRACTION, Res_value::COMPLEX_UNIT_FRACTION, 1.0f/100 },
4372    { "%p", strlen("%p"), Res_value::TYPE_FRACTION, Res_value::COMPLEX_UNIT_FRACTION_PARENT, 1.0f/100 },
4373    { NULL, 0, 0, 0, 0 }
4374};