Preference Crash When getSummary() Contains '%'

发表于 |

当 ListPreference 中执行 getSummary 的时候碰到了字符 ‘%’ 时会导致应用 crash。

解决方式

重写 ListPreference 的 getSummary 方法，避免在遇到 ‘%’ 的时候 crash。

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private class NoneFormatSummaryListPreference extends ListPreference {

	public NoneFormatSummaryListPreference(Context context) {
		super(context);
	}

	@Override
	public CharSequence getSummary() {
		try {
			// for call super.super.getSummary()
			CharSequence[] entries = super.getEntries();
			super.setEntries(null);
			CharSequence result = super.getSummary();
			super.setEntries(entries);
			return result;
			// return super.getSummary();
		} catch (Exception e) {
			e.printStackTrace();
			return "";
		}
	}
}

原理

以下内容皆引用自 Preference Summary or Secondary Text :

A note about ListPreference. In android doc we can read:

If the summary has a String formatting marker in it (i.e. “%s” or “%1$s”), then the current entry value will be substituted in its place when it’s retrieved.

As a result, if you set “summary” that contains “%” char (like “5%”), you can have java.util.UnknownFormatConversionException: Conversion: because it may be an unknown format.
The reason is here (standard method in ListPreference)

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@Override
public CharSequence getSummary() { 
	final CharSequence entry = getEntry(); 
	if (mSummary == null || entry == null) { 
		return super.getSummary(); 
	} else { 
		return String.format(mSummary, entry); 
	} 
}

If you want to use value like “5%” in ListPreference, in API Level 11 or higher, you need to be careful.
I suggest you create a subclass of ListPreference, override getSummary() method and return whatever you need, skipping the call to String.format().
Alternatively you can obtain percent character in String.format() by specifying “%%”.

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