Assignments are not expressions - Kotlin

Question

I'm refactoring my project built with Java to Kotlin and to copy database from sqlite assets table I'm doing this and it works correctly.

private void copyDataBase() throws IOException {
        InputStream mInput = mContext.getAssets().open(DB_NAME);
        String outFileName = DB_PATH + DB_NAME;
        OutputStream mOutput = new FileOutputStream(outFileName);
        byte[] mBuffer = new byte[1024];
        int mLength;
        while ((mLength = mInput.read(mBuffer)) > 0) {
            mOutput.write(mBuffer, 0, mLength);
        }
        mOutput.flush();
        mOutput.close();
        mInput.close();
    }

How do I deal with "Assignments are not expressions, and only expressions are allowed in this context"?

@Throws(IOException::class)
    private fun copyDataBase() {
        val mInput = mContext.assets.open(DB_NAME)
        val outFileName = DB_PATH + DB_NAME
        val mOutput = FileOutputStream(outFileName)
        val mBuffer = ByteArray(1024)
        var mLength: Int
        while ((mLength = mInput.read(mBuffer)) > 0) {
            mOutput.write(mBuffer, 0, mLength)
        }
        mOutput.flush()
        mOutput.close()
        mInput.close()
    }

Error is here

while ((mLength = mInput.read(mBuffer)) > 0) {
            mOutput.write(mBuffer, 0, mLength)
        }

Thank you.

Answer 1

Change it to:

 mLength = mInput.read(mBuffer)
 while (mLength > 0) { 
        mOutput.write(mBuffer, 0, mLength)
        mLength = mInput.read(mBuffer)
    }

Answer 2

This is a work around to your problem:

while ({mLength = mInput.read(mBuffer); mLength}() > 0) {
    mOutput.write(mBuffer, 0, mLength)
}

For further detail read this discussion.