尝试设置折叠工具栏布局的副标题时获得'java.lang.ClassCastException'

Question

我正在尝试使用此示例在我的应用程序中设置CollapsingToolbarLayout的"副标题"。

这是Profile.java onCreate()的代码：

    CollapsingToolbarLayout collapsingToolbarLayout;
    Toolbar toolbar;
    HeaderView toolbarHeaderView;
    HeaderView floatHeaderView;
    collapsingToolbarLayout = (CollapsingToolbarLayout) findViewById(R.id.collapse_toolbar);
    // error on the line below
    toolbarHeaderView = (HeaderView) findViewById(R.id.toolbar_header_view);
    floatHeaderView = (HeaderView) findViewById(R.id.float_header_view);
    toolbarHeaderView.bindTo("title", "subtitle");
    floatHeaderView.bindTo("title", "subtitle");

这是activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    android:id="@+id/coordinatorLayout"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.abc.zzz.Profile">
    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBarLayout"
        android:layout_width="match_parent"
        android:layout_height="256dp"
        android:theme="@style/AppTheme.AppBarOverlay"
        android:fitsSystemWindows="true">
        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapse_toolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:contentScrim="@color/colorPrimary"
            android:fitsSystemWindows="true"
            app:popupTheme="@style/AppTheme.PopupOverlay">
            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="parallax">
                <include
                    android:id="@+id/toolbar_header_view"
                    layout="@layout/header_view"
                    android:layout_height="wrap_content"
                    android:layout_width="match_parent"
                    android:layout_marginRight="@dimen/header_view_end_margin_right"
                    android:layout_marginEnd="@dimen/header_view_end_margin_right"
                    android:visibility="gone"
                    />
            </android.support.v7.widget.Toolbar>
        </android.support.design.widget.CollapsingToolbarLayout>
    </android.support.design.widget.AppBarLayout>
    <include
        android:id="@+id/float_header_view"
        layout="@layout/header_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_behavior="com.abc.zzz.ViewBehavior"/>
</android.support.design.widget.CoordinatorLayout>

这是header_view.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
    <!-- Title -->
    <TextView
        android:id="@+id/header_view_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@android:color/white"
        android:textSize="18sp"
        />
    <!-- Subtitle -->
    <TextView
        android:id="@+id/header_view_sub_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="@android:color/white"
        android:textSize="16sp"
        />
</LinearLayout>

这是HeaderView.java：

public class HeaderView extends LinearLayout {
    TextView title;
    TextView subTitle;
    public HeaderView(Context context) {
        super(context);
    }
    public HeaderView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    public HeaderView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public HeaderView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        title = (TextView) findViewById(R.id.header_view_title);
        subTitle = (TextView) findViewById(R.id.header_view_sub_title);
    }
    public void bindTo(String title) {
        bindTo(title, "");
    }
    public void bindTo(String title, String subTitle) {
        hideOrSetText(this.title, title);
        hideOrSetText(this.subTitle, subTitle);
    }
    private void hideOrSetText(TextView tv, String text) {
        if (text == null || text.equals(""))
            tv.setVisibility(GONE);
        else
            tv.setText(text);
    }
}

这是ViewBehavior.java：

public class ViewBehavior extends CoordinatorLayout.Behavior<HeaderView> {
    private Context mContext;
    private int mStartMarginLeft;
    private int mEndMargintLeft;
    private int mMarginRight;
    private int mStartMarginBottom;
    private boolean isHide;
    public ViewBehavior(Context context, AttributeSet attrs) {
        mContext = context;
    }
    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, HeaderView child, View dependency) {
        return dependency instanceof AppBarLayout;
    }
    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, HeaderView child, View dependency) {
        shouldInitProperties(child, dependency);
        int maxScroll = ((AppBarLayout) dependency).getTotalScrollRange();
        float percentage = Math.abs(dependency.getY()) / (float) maxScroll;
        float childPosition = dependency.getHeight()
                + dependency.getY()
                - child.getHeight()
                - (getToolbarHeight() - child.getHeight()) * percentage / 2;

        childPosition = childPosition - mStartMarginBottom * (1f - percentage);
        CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) child.getLayoutParams();
        lp.leftMargin = (int) (percentage * mEndMargintLeft) + mStartMarginLeft;
        lp.rightMargin = mMarginRight;
        child.setLayoutParams(lp);
        child.setY(childPosition);
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
            if (isHide && percentage < 1) {
                child.setVisibility(View.VISIBLE);
                isHide = false;
            } else if (!isHide && percentage == 1) {
                child.setVisibility(View.GONE);
                isHide = true;
            }
        }
        return true;
    }
    private void shouldInitProperties(HeaderView child, View dependency) {
        if (mStartMarginLeft == 0)
            mStartMarginLeft = mContext.getResources().getDimensionPixelOffset(R.dimen.header_view_start_margin_left);
        if (mEndMargintLeft == 0)
            mEndMargintLeft = mContext.getResources().getDimensionPixelOffset(R.dimen.header_view_end_margin_left);
        if (mStartMarginBottom == 0)
            mStartMarginBottom = mContext.getResources().getDimensionPixelOffset(R.dimen.header_view_start_margin_bottom);
        if (mMarginRight == 0)
            mMarginRight = mContext.getResources().getDimensionPixelOffset(R.dimen.header_view_end_margin_right);
    }

    public int getToolbarHeight() {
        int result = 0;
        TypedValue tv = new TypedValue();
        if (mContext.getTheme().resolveAttribute(android.R.attr.actionBarSize, tv, true)) {
            result = TypedValue.complexToDimensionPixelSize(tv.data, mContext.getResources().getDisplayMetrics());
        }
        return result;
    }
}

问题是我收到此错误：java.lang.RuntimeException: Unable to start activity ComponentInfo{com.abc.zzz/com.abc.zzz.Profile}: java.lang.ClassCastException: android.widget.LinearLayout cannot be cast to com.abc.zzz.HeaderView上面指定的行上。

为什么我会收到此错误以及如何解决它？

请让我知道。

Answer 1

你没有在你的代码上显示，但我敢打赌你的header_view.xml有一个LinearLayout作为根视图。

所以基本上发生的情况是：<include代码被header_view.xml根目录的LinearLayout"替换"，然后你调用findViewById(R.id.toolbar_header_view)返回该LinearLayout，然后用(HeaderView)告诉虚拟机这是一个HeaderView，但它是一个LinearLayout。所以它崩溃了！

没有看到您未显示的代码段的最佳选择是以下选项之一：

1. 把<HeaderView>放在header_view.xml的根源，

或者如果这是不可能的，因为里面有更多的东西header_view.xml

2. 更改代码以查找include，然后在包含中查找实际的 HeaderView。

像这样：

toolbarHeaderView = (HeaderView) findViewById(R.id.toolbar_header_view).findViewById(R.id.header_view_id);
floatHeaderView = (HeaderView) findViewById(R.id.float_header_view).findViewById(R.id.header_view_id);

请注意，它会调用findViewById两次。一个用于包含，另一个用于其中的标题视图