Why is my startActivityForResult() returning null when converting ArrayList<String> to String[]?

Question

The following code is throwing a NullPointerException because the ArrayList isn't being converted to an Array correctly. The array is supposed to be passed to another activity. This works because I can pass a regular String[] but when I try to convert an ArrayList to Array I get the error. What's the right way to convert ArrayList to Array?

String[] tmpHtml = new String[(siteElements.size())];
tmpHtml = (String[]) siteElements.toArray();
Intent returnResult = new Intent();
returnResult.putExtra("elements", tmpHtml);
setResult(RESULT_OK, returnResult);
finish();

I would have expected a ClassCastException. toArray with no argument returns an Object[]. — Patricia Shanahan
– Patricia Shanahan, Commented Mar 14, 2013 at 1:35

Changwei Yao · Accepted Answer · 2013-03-14 01:34:13Z

3

The way you covert the ArrayList to String array was wrong. The correct way is:

tmpHtml = siteElements.toArray(tmpHtml);

answered Mar 14, 2013 at 1:34

Changwei Yao

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Shuai · Accepted Answer · 2013-03-14 01:56:47Z

0

Changwei Yao's answer will work, but why not

// put to intent
returnResult.putStringArrayListExtra("elements", siteElements);
// Get from intent
returnResult.getStringArrayListExtra("elements");

answered Mar 14, 2013 at 1:56

Shuai

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