Atomic Updates
The Preferences API does not provide database-like "transactions" wherein multiple preferences are modified atomically. Occasionally, it is necessary to modify two or more preferences as a unit.
For example, suppose you are storing the x and y coordinates where a window is to be placed. The only way to achieve atomicity is to store both values in a single preference. Many encodings are possible. Here's a simple one:
int x, y;
...
prefs.put(POSITION, x + "," + y);
When such a "compound preference" is read, it must be decoded. For robustness, allowances should be made for a corrupt (unparseable) value:
static int X_DEFAULT = 50, Y_DEFAULT = 25;
void parsePrefs() {
String position = prefs.get(POSITION, X_DEFAULT + "," + Y_DEFAULT);
int x, y;
try {
int i = position.indexOf(',');
x = Integer.parseInt(coordinates.substring(0, i));
y = Integer.parseInt(position.substring(i + 1));
} catch(Exception e) {
// Value was corrupt, just use defaults
x = X_DEFAULT;
y = Y_DEFAULT;
}
...
}