Double parameter with 2 digits after dot in string

问题:

I want to have a parameter in one string in strings.xml and this parameter should be a double value. So I use %1$f. Here - http://developer.android.com/reference/java/util/Formatter.html there are many examples, but what if I want to have have a few double/float parameters and I want only the second one to have 2 digits after .? I tried to use combinations like %2$.2f or %2.2$f. Nor of them worked. %.1f does not work as well. So, does anybody know how can I "customize" a float/double value inside a strings.xml? Thanks.

回答1:

If it were me I'd store the values in the resources as simple values, and then use formatter methods to control how they're displayed, roughly like this

public String formatFigureTwoPlaces(float value) {
    DecimalFormat myFormatter = new DecimalFormat("##0.00");
    return myFormatter.format(value);
}

public String formatFigureOnePlace(float value) {
    DecimalFormat myFormatter = new DecimalFormat("##0.0");
    return myFormatter.format(value);
}

回答2:

Just adding to @David Airam's answer here; the "incorrect" solution he gives is actually correct, but with a bit of tweaking. The XML file should contain:

<string name="resource1">Hello string: %1$s, and hello float: %2$.2f.</string>

Now in the Java code:

String svalue = "test";
float sfloat= 3.1415926;
String sresult = getString(R.string.resource1, svalue, sfloat);

The exception that @David Airam reported is from trying to jam a String into a format specifier with %f, which requires a floating point type. Use float and there is no such exception.

Also, you can use Float.valueOf() to convert a String to a float in case your input data was originally a string (say, from a EditText or something). However, you should always try/catch valueOf() operations and handle the NumberFormatException case, since this exception is unchecked.

回答3:

%.1f work for me if you like to show only 1 digit after ','

回答4:

I now that this reply is arriving too late... but I hope to be able to help other people:

Android sucks with multiple parameters substitutions when you want decimal numbers and format this in common style %a.bf

The best solution I have found (and only for these kind of resources) is put the decimal parameters as strings %n$s and in the code apply my conversion with String.format(...)

Example:

INCORRECT WAY:

// In xml file:

<string name="resource1">You has a desviation of %1$s and that is a %2$.2f%% percentage.</string>

// And in java file

  String sresult = getString(R.string.resource1, svalue, spercentage); // <-- exception!

This solution is technically correct but incorrect due to android substitution resources system so the last line will generate an exception.

CORRECT WAY / SOLUTION:

Simply convert the second parameter into a String.

<string name="resource1">You has a desviation of %1$s and that is a %2$s percentage.</string>

And now in the code:

...

  // This is the auxiliar line added to solve the problem
  String spercentage = String.format("%.2f%%",percentage);

  // This is the common code where we use the last variable.
  String sresult = getString(R.string.resource1, svalue, spercentage);