CODEWITHSUNDEEP
androidcustom-componentscrollview
beetstra
beetstra

Reputation: 7952

Programmatically creating scrollview(s) from custom component in android

I'm trying to build a compound control in Android, containing (among other things) a ScrollView. Things go wrong when I try to view the control in Eclipse, crashing with a NullPointerException after the error message: "Parser is not a BridgeXmlBlockParser".

Stacktrace:

java.lang.NullPointerException
at android.view.View.<init>(View.java:1720)
at android.view.ViewGroup.<init>(ViewGroup.java:277)
at android.widget.FrameLayout.<init>(FrameLayout.java:83)
at android.widget.ScrollView.<init>(ScrollView.java:128)
at android.widget.ScrollView.<init>(ScrollView.java:124)
at android.widget.ScrollView.<init>(ScrollView.java:120)
at my.compound.control.StringPicker.onMeasure(StringPicker.java:46)
...

I've traced the error to the following conditions:

There is a workaround of course, which is passing the attrs I receive when Eclipse constructs the compound control, but I don't want all the attributes set on the compound control to apply to my inner control.

Am I doing something wrong, is this a bug in Android Eclipse, ...?

This is what my.compound.control.StringPicker.onMeasure looks like (stripped it a bit for clarity):

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    if (this.getChildCount() != requestedLength) {
        this.removeAllViews();
        int childWidth = getWidth() / requestedLength;
        int childHeight = getHeight();
        for (int i = 0; i < requestedLength; i++) {
            ScrollView child = new ScrollView(getContext()); // NPE here
            child.setLayoutParams(new LayoutParams(childWidth, childHeight));
            addView(child);
        }
    }
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

Upvotes: 3

Views: 2109

Answers (2)

beetstra
beetstra

Reputation: 7952

It seems to have been a bug in older Android versions.

The problem does not appear in Android version 2.3 or higher, but does appear when selecting Android 2.2 or lower. The workaround for these older Android versions is (as mentioned in the question) to copy the attrs parameter from the constructor.
This is only needed if you want to use design-view in Eclipse with these older versions, to run your application in the older versions no workaround is necessary.

Upvotes: 0

Andrei
Andrei

Reputation: 2337

How are you creating your compound control, via XML layout or dynamically in the code? A possible reason I could think of is that you are adding it via XML but you may not have added the StringPicker(Context context, AttributeSet attrs) constructor. There you should call super(context, attrs).

Upvotes: 1

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