android.view.ViewGroup$LayoutParams 不能强制转换为 android.widget.A

Question

我得到了这个解释：

java.lang.ClassCastException: android.view.ViewGroup$LayoutParams cannot be cast to android.widget.AbsListView$LayoutParams
at android.widget.ListView.setupChild(ListView.java:1806)
at android.widget.ListView.makeAndAddView(ListView.java:1775)
at android.widget.ListView.fillDown(ListView.java:672)
at android.widget.ListView.fillFromTop(ListView.java:732)
at android.widget.ListView.layoutChildren(ListView.java:1625)
at android.widget.AbsListView.onLayout(AbsListView.java:1863)
at android.view.View.layout(View.java:11278)
at android.view.ViewGroup.layout(ViewGroup.java:4224)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1628)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1486)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1399)
at android.view.View.layout(View.java:11278)
at android.view.ViewGroup.layout(ViewGroup.java:4224)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1628)
at android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1617)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1401)
at android.view.View.layout(View.java:11278)
at android.view.ViewGroup.layout(ViewGroup.java:4224)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1628)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1486)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1399)
at android.view.View.layout(View.java:11278)
at android.view.ViewGroup.layout(ViewGroup.java:4224)
at android.widget.FrameLayout.onLayout(FrameLayout.java:431)
at android.view.View.layout(View.java:11278)
at android.view.ViewGroup.layout(ViewGroup.java:4224)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1628)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1486)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1399)
at android.view.View.layout(View.java:11278)
at android.view.ViewGroup.layout(ViewGroup.java:4224)
at android.widget.FrameLayout.onLayout(FrameLayout.java:431)
at android.view.View.layout(View.java:11278)
at android.view.ViewGroup.layout(ViewGroup.java:4224)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1504)
at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2458)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4424)
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)

但问题是我找不到问题的根源。究竟在哪里，这意味着什么？

为什么是小部件

，我没有任何小部件！

法典：

不确定这里是否：

public class MyListPreference extends ListPreference {
    public MyListPreference(Context context) {
        super(context);
    }
    public MyListPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected View onCreateDialogView() {
        TextView dialogTitle = (TextView)super.onCreateDialogView();
        if (dialogTitle != null) {
            // Dialog
            dialogTitle.setBackgroundColor(getContext().getResources().getColor(R.color.category_background));
            dialogTitle.setPadding(10, 4, 4, 4);
            // Text
            dialogTitle.setTextSize(14);
            dialogTitle.setTypeface(null, Typeface.BOLD);
            dialogTitle.setTextColor(getContext().getResources().getColor(R.color.actionbar_background));
            dialogTitle.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        }
        return dialogTitle;
    }
}

Answer 1

dialogTitle.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));

在这里，您将正确类型AbsListView.LayoutParams的现有布局参数替换为更通用的ViewGroup.LayoutParams。布局参数类型是视图的父容器的类型。

如果需要修改现有布局参数，请使用 getLayoutParams() 访问它们，对其进行修改，然后调用 requestLayout() 以通知布局已更改。

例。而不是

fooView.setLayoutParams(new LayoutParams(123, 456));

做

LayoutParams lp = fooView.getLayoutParams();
lp.width = 123;
lp.height = 456;
fooView.requestLayout();

Answer 2

替换

imageView.setLayoutParams(new LayoutParams(123, 456));

跟

imageView.setLayoutParams(new  android.widget.AbsListView.LayoutParams(123, 456));

这对我有用

Answer 3

此错误是由于ListView中的代码造成的。

总之，如果它直接用作ListView中的子项，我们应该只将AbsListView.LayoutParams设置为 View .

原因如下。

onMeasure() ListView：

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//...
    // Lay out child directly against the parent measure spec so that
    // we can obtain exected minimum width and height.
    measureScrapChild(child, 0, widthMeasureSpec, heightSize);
//...
}
private void measureScrapChild(View child, int position, int widthMeasureSpec, int heightHint) {
    LayoutParams p = (LayoutParams) child.getLayoutParams();
    if (p == null) {
        p = (AbsListView.LayoutParams) generateDefaultLayoutParams();
        child.setLayoutParams(p);
    }
    //...
}

因此，如果项目视图已经具有ViewGroup.LayoutParams，则不会覆盖AbsListView.LayoutParams。但是，在setupChild、layoutChildren和许多其他方法中，ListView总是将项目视图的LayoutParams投射到AbsListView.LayoutParams中。如

private void setupChild(View child, int position, int y, boolean flowDown, int childrenLeft,
            boolean selected, boolean isAttachedToWindow) {
    //...
    // Respect layout params that are already in the view. Otherwise make
    // some up...
    AbsListView.LayoutParams p = (AbsListView.LayoutParams) child.getLayoutParams();
    if (p == null) {
        p = (AbsListView.LayoutParams) generateDefaultLayoutParams();
    }
    //...
}