java.lang.ClassCastException: GridLayout.LayoutParams无法转换为Frame.LayoutParams

Question

java.lang.ClassCastException: GridLayout.LayoutParams无法转换为Frame.LayoutParams

javaandroidxmlandroid-layoutandroid-studio

3

使用 Android Studio 2.0 的 OS X Yosemite 10.10.5。

为了教学目的，我希望尽可能多地将 View 属性从 XML 移动到 Java。

我在一个 GridLayout 中放置了一个 android.support.v7.widget.RecyclerView，并希望移动 RecyclerView 的 android:layout_gravity。

根据 GridLayout.setGravity 和 R.attr 文档，我知道 layout_gravity 被子对象用于在父对象中设置对齐方式属性。

以下代码是异常的根本原因：

GridLayout.LayoutParams parentParams = new GridLayout.LayoutParams();
parentParams.setGravity(Gravity.CENTER_VERTICAL);
container.setLayoutParams(parentParams);

我想要压缩的XML：

<GridLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/recycler_view_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/alphabet_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    <!--android:layout_gravity="center_vertical">-->
    </android.support.v7.widget.RecyclerView>

</GridLayout>

以下是异常链：

java.lang.ClassCastException: android.widget.GridLayout$LayoutParams cannot be cast to android.widget.FrameLayout$LayoutParams
at android.widget.FrameLayout.onMeasure(FrameLayout.java:431)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
at android.view.View.measure(View.java:17430)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
at android.view.ViewRootImpl$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)

我查了一下 android.view.View.measure(View.java:17430) ，找到了这个信息：

if (cacheIndex < 0 || sIgnoreMeasureCache) {
    // measure ourselves, this should set the measured dimension flag back
    onMeasure(widthMeasureSpec, heightMeasureSpec);
    mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
} else {

我不太明白为什么会调用 android.support.v7.widget.ContentFrameLayout.onMeasure 而不是 android.view.View.onMeasure

我错过了什么吗？

- Paul

请显示一下容器是什么 -- container.setLayoutParams(parentParams); - dione llorera

@dione llorera 容器是一个 GridLayout。 - Paul

@MPG 你说的是哪个导入语句？ - Paul

1个回答

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- stkent · Accepted Answer

在您提供的代码片段中：

GridLayout.LayoutParams parentParams = new GridLayout.LayoutParams();
parentParams.setGravity(Gravity.CENTER_VERTICAL);
container.setLayoutParams(parentParams);

从变量名container来看，您似乎试图将构造的LayoutParams应用于GridLayout实例而不是RecyclerView实例。我希望最终的代码行看起来更像是这样：

recyclerView.setLayoutParams(parentParams);

如果我的假设是正确的，那么你的GridLayout的父级将尝试解析你构建的LayoutParams。这个父级很可能(!)不是一个GridLayout(我猜测从堆栈跟踪中它是一个FrameLayout)，并且在尝试处理GridLayout特定的LayoutParams时出现了问题。