java.lang.ClassCastException: android.view.ViewGroup$LayoutParams cannot be cast to android.view.Vie

java.lang.ClassCastException: android.view.ViewGroup$LayoutParams cannot be cast to android.view.ViewGroup$MarginLayoutParams
        at com.mystudy.studyviews.views.ViewGroupView.onMeasure(ViewGroupView.java:60)
        at android.view.View.measure(View.java:22002)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
        at android.view.View.measure(View.java:22002)
        at androidx.constraintlayout.widget.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:1227)
        at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1572)
        at android.view.View.measure(View.java:22002)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
        at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
        at android.view.View.measure(View.java:22002)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
        at androidx.appcompat.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:401)
        at android.view.View.measure(View.java:22002)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
        at android.view.View.measure(View.java:22002)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1514)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:806)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:685)
        at android.view.View.measure(View.java:22002)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6580)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
        at com.android.internal.policy.DecorView.onMeasure(DecorView.java:721)
        at android.view.View.measure(View.java:22002)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2410)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1498)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1751)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1386)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6733)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:911)
        at android.view.Choreographer.doCallbacks(Choreographer.java:723)
        at android.view.Choreographer.doFrame(Choreographer.java:658)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:897)
        at android.os.Handler.handleCallback(Handler.java:789)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6541)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

为什么不能转化？明明是父子类的关系。百思不得其解啊。

这个是我在自定义ViewGroup中使用的部分代码：

View childrenView= getChildAt(i);
cwidth=childrenView.getMeasuredWidth();
cheight=childrenView.getMeasuredHeight();
MarginLayoutParams cParams= (MarginLayoutParams) childrenView.getLayoutParams();

 ViewGroup.MarginLayoutParams明明是继承ViewGroup.LayoutParams的，为什么就是不能向下转型呢？

最后在各种情况下的推断中发现：

View childrenView= getChildAt(i);
cwidth=childrenView.getMeasuredWidth();
cheight=childrenView.getMeasuredHeight();
MarginLayoutParams cParams= new MarginLayoutParams(cwidth,cheight);

把代码改成这样就可以了，不会再报那个错误了。

最终我认为在自定义ViewGroup中ViewGroup.MarginLayoutParams是不会自己创建的。

最后

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