Kotlin如何调用扩展功能

Question

I want to call an extension function from MainActivity class in another class. How can i do this?

object MainActivity : AppCompatActivity() {

val StringBuilder.readHistory: StringBuilder
    get() {
        val temp = this@readHistory
        temp.setLength(0)
        try {
            val file = InputStreamReader(MainActivity.openFileInput(MainActivity.getString(R.string.dosyaadı)))
            val br = BufferedReader(file)
            var line = br.readLine()
            while (line != null) {
                temp.append(line + "\n")
                line = br.readLine()
            }
            br.close()
            file.close()
} catch (e: Exception) {
            e.printStackTrace()
        }
        return temp
    }

Answer 1

You can't call this outside of the class, because it's nested inside this class and therefore only applies to that scope.

Make the extension property top-level (move it outside of the class).

Answer 2

成员扩展仅在声明它们的类中可见。但是，您可以将扩展功能放在类之外，以便能够在其他任何地方导入和使用它。