Question

I’ve just run into an issue when attempting to grab a custom View using findViewById(). The custom view otherwise displays and operates correctly. Unfortunately, I need to be able to change some data it displays at will, so it has to be done.

My XML looks like this:

<?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">

  <com.TheProject.TheApp.Chart 
    android:id="@+id/chart"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
  />

</LinearLayout>

I know sometimes the issue is that people accidentally name the component “View” in the XML instead of their subclass of it.

Inside my Activity’s onCreate() method, I have this:

myChart=(Chart)findViewById(R.id.chart); //where myChart is an object of type Chart

That throws a ClassCastException.

I decided to experiment a little and instead changed the line to this to see if I still recieved a ClassCastException:

View chart=(View)findViewById(R.id.chart);

This worked fine, which tells me that findViewById has no trouble giving me a View. But it doesn’t want to give me a Chart.

As far as the Chart class goes, it’s a really simple subclass of View that appears to otherwise work correctly.

public class Chart extends View{
    public Chart(Context context) {
    super(context);     
    init();
}

public Chart(Context context, AttributeSet attrs) {
    super(context, attrs);      
    init();
}

public Chart(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);        
    init();     
}
    /* More stuff below like onDraw, onMeasure, setData, etc. */
}

I’m probably just doing something stupid. Do you guys have any ideas? Thanks for your help!

Answer 1

Just out of curiosity, is that xml being used in another layout with an <include> tag?

I had an issue just like this where we were including another xml layout in a viewflipper with

<include layout="@layout/some_layout.xml"> and findviewbyid was getting the wrong widgets. I had to wrap the whole external layout in <merge></merge> tags to allow it to merge correctly into the base layout.

Try changing your layout to this, if it’s being included.

<?xml version="1.0" encoding="utf-8"?>
<merge>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="match_parent"
  android:layout_height="match_parent">

  <com.TheProject.TheApp.Chart 
    android:id="@+id/chart"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
  />

</LinearLayout>
</merge>

edit: check out this link about how merge works