Why hasn't the string been replaced when it is from string resource file in Kotlin?

Question

When I use Code A, I get the original string ,why?

Code B can replace string both ${myObject.status} and ${myObject.name}, the result is OK.

Image

Code A

<string name="DetailsOfWiFiDef">The WiFi status is ${myObject.status},
        the name of WiFi is ${myObject.name}\n\n
</string>

val myObject=getIt()
val s=mContext.getString(R.string.DetailsOfWiFiDef)
val sb = StringBuilder()
sb.append(s)  //The string keep original

Code B

val myObject=getIt()
val k="The WiFi status is ${myObject.status},the name of WiFi is ${myObject.name} \n"
val sb = StringBuilder()
sb.append(k)  //It has been replaced

Pawel · Accepted Answer · 2018-06-30 10:22:01Z

2

Kotlin compiler converts string literals into StringBuilder chain at compile time:

// code in Kotlin
val k = "The WiFi status is ${myObject.status},the name of WiFi is ${myObject.name} \n"

// is converted into equivalent of code in Java
String k = new StringBuilder("The WiFi status is ").append(myObject.getStatus()).append(",the name of WiFi is ").append(myObject.getName()).append(" \n");

If you load through resources there's no conversion, it's used as is. However you can use formattable string resource:

<string name="DetailsOfWiFiDef">The WiFi status is %1$s,
        the name of WiFi is %2$s\n\n
</string>

Then inject arguments when reading string (Android Studio even corrects You if you proide too many arguments or wrong type in real time):

val s=mContext.getString(R.string.DetailsOfWiFiDef, myObject.status, myObject.name)

answered Jun 30, 2018 at 10:22

Pawel

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