问题
I'm trying to set 'Sub-title' of a CollapsingToolbarLayout in my app using this example here.
Here's the code from onCreate() of Profile.java:
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");
Here's 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>
Here's 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>
Here's 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);
}
}
Here's 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;
}
}
The problem is that I'm getting this error: 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 on the line specified above.
Why am I getting this error and how to resolve it?
Please let me know.
回答1:
You didn't show on your code but I bet that your header_view.xml have a LinearLayout as the root view.
So basically what happens is: the <include code "gets replaced" by the LinearLayout at the root of header_view.xml and then you call findViewById(R.id.toolbar_header_view) which returns that LinearLayout and then with the (HeaderView) you're telling the VM this is a HeaderView, but it's, it's a LinearLayout. So it crashes!
The best option without seeing piece of code you didn't show it is one of the following:
- put
<HeaderView>at the root ofheader_view.xml,
or if that is not possible because there's more stuff inside header_view.xml
- change your code to find the
includeand then inside the include, to find the actual HeaderView.
Something like:
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);
note that it calls findViewById two times. One for the include and another for the HeaderView inside it
来源：https://stackoverflow.com/questions/41492631/getting-java-lang-classcastexception-while-trying-to-set-subtitle-of-a-collaps