Android，可以在 XML 中添加片段，但不能通过代码 [重复]答案

【问题标题】：Android, Can add Fragment in XML, but not via Code [duplicate]Android，可以在 XML 中添加片段，但不能通过代码 [重复]
【发布时间】：2020-01-30 09:50:28
【问题描述】：

我有一个片段，当通过 XML 添加时，

  <fragment
            class="my.fragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:tag="config" />

它已成功添加到视图中，我可以与之交互。但是，当我尝试以编程方式添加它时，在滚动视图中，作为第二个孩子：

    val layout = FrameLayout(this)
    val params = FrameLayout.LayoutParams(FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT)
    layout.layoutParams = params
    layout.id = View.generateViewId()
    scrollview_container.addView(layout, params)

    val f2 = MyFragment.newInstance(Gson().toJson(asset))
    val trans = supportFragmentManager.beginTransaction()

    trans.add(layout.id, f2, "config")
    trans.addToBackStack(null)
    trans.commit()

我收到以下错误（对不起，它很长）

E/AndroidRuntime: FATAL EXCEPTION: main
Process: my.process, PID: 4950
java.lang.ClassCastException: android.view.ViewGroup$LayoutParams cannot be cast to android.view.ViewGroup$MarginLayoutParams
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6819)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.view.View.measure(View.java:24530)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
    at android.view.View.measure(View.java:24530)
    at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1414)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.widget.ScrollView.onMeasure(ScrollView.java:452)
    at android.view.View.measure(View.java:24530)
    at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:735)
    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:481)
    at android.view.View.measure(View.java:24530)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
    at android.view.View.measure(View.java:24530)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
    at android.view.View.measure(View.java:24530)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at android.view.View.measure(View.java:24530)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
    at android.view.View.measure(View.java:24530)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
    at com.android.internal.policy.DecorView.onMeasure(DecorView.java:742)
    at android.view.View.measure(View.java:24530)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:3006)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1833)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2122)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1721)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7598)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:966)
    at android.view.Choreographer.doCallbacks(Choreographer.java:790)
    at android.view.Choreographer.doFrame(Choreographer.java:725)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:951)
    at android.os.Handler.handleCallback(Handler.java:883)
    at android.os.Handler.dispatchMessage(Handler.java:100)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

此堆栈跟踪中没有应用程序代码，只有 Android SDK 调用。我也尝试将我的片段添加到 NavHostFragment 中，但我仍然遇到同样的错误。

有什么想法吗？提前致谢！

【问题讨论】：

ViewGroup.MarginLayoutParams 是预期的。我什至等了一会儿才按下“关闭”按钮。
@MartinZeitler 很好，你已经等了，但除了我的问题与边距无关，使用 val params = ViewGroup.MarginLayoutParams(ViewGroup.MarginLayoutParams.MATCH_PARENT, ViewGroup.MarginLayoutParams.MATCH_PARENT)似乎不起作用。所以，请尝试以明智和完整的方式回答。
这个问题通常有点不清楚，因为不知道scrollview_container 是什么......似乎你在ScrollView 上设置FrameLayout.LayoutParams（预计@987654331 @ 作为第二个参数），而不是在 FrameLayout 上设置它们。
然后首先要求澄清。 scrollview_container 是滚动视图的唯一子项。它是一个LinearLayout，其中添加了我创建的FrameLayout。然后在 FrameLayout 中尝试添加片段。
请先阅读How to create a Minimal, Reproducible Example，然后再尝试教育我。一旦你有了这样一个（注意edit 按钮），你最终仍然可以重新打开这个问题。

标签： android xml fragment

【解决方案1】：

尝试在您的代码中更改以下行：

val params = FrameLayout.LayoutParams(FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT)

收件人：

val params = ScrollView.LayoutParams(ScrollView.LayoutParams.MATCH_PARENT, ScrollView.LayoutParams.MATCH_PARENT);

【讨论】：

【解决方案2】：

您的 Fragment 似乎已经有布局参数。除了更改它们，您应该像这样修改现有参数。

    ViewGroup.LayoutParams params = yourfragment.getView().getLayoutParams();
    params.width = ViewGroup.LayoutParams.MATCH_PARENT;
    params.height = ViewGroup.LayoutParams.MATCH_PARENT;
    contactsFragment.getView().requestLayout();

答案是 java 语言，但你会从这里得到概念。

【讨论】：