Arduino SD card shield and RTC Cannot write in datalog with time - android-sdcard

Question

we been working on the SD card module and RTC, The main purpose of this is just to display the time and date then store the data to the SD card it's reading just fine but soon as we read the txt file it came out empty. my question is how can we display the data log in our txt file? here's the code:
#include <SD.h>
#include "RTClib.h"
const int chipSelect = 4;
int i=0;
int t;
#if defined(ARDUINO_ARCH_SAMD)
#define Serial SerialUSB
#endif
RTC_Millis rtc;
void setup(void)
{
Serial.begin(9600);
Serial.println("MICRO"); //Test the serial monitor
//RTC Module Initialization
while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only
}
rtc.begin(DateTime(_DATE_,__TIME__));
delay(2000);
//SD Card Module Initialization
Serial.print("Initializing SD card...");
// make sure that the default chip select pin is set to
// output, even if you don't use it:
pinMode(10, OUTPUT);
// see if the card is present and can be initialized:
if (!SD.begin(chipSelect)) {
Serial.println("Card failed, or not present");
// don't do anything more:
}
Serial.println("card initialized.");
delay(500);
}
void loop() {
//DATE&TIME
DateTime now = rtc.now();
Serial.print(now.year(), DEC);
Serial.print('/');
Serial.print(now.month(), DEC);
Serial.print('/');
Serial.print(now.day(), DEC);
Serial.print(' ');
Serial.print(now.hour(), DEC);
Serial.print(':');
Serial.print(now.minute(), DEC);
Serial.print(':');
Serial.print(now.second(), DEC);
Serial.println();
//delay(3000);
delay(2000);
//SD.begin(chipSelect);
//DATALOGGING w DATE&TIME STAMP
i++;
int erick=i%5;
// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
if (erick==0){
File dataFile = SD.open("datalog.txt", FILE_WRITE);
// if the file is available, write to it:
if (dataFile) {
dataFile.println();
dataFile.print(now.year(), DEC);
dataFile.print('/');
dataFile.print(now.month(), DEC);
dataFile.print('/');
dataFile.print(now.day(), DEC);
dataFile.print(' ');
dataFile.print(now.hour(), DEC);
dataFile.print(':');
dataFile.print(now.minute(), DEC);
dataFile.print(':');
dataFile.print(now.second(), DEC);
dataFile.print(' ');
}
// if the file isn't open, pop up an error:
else {
Serial.println("error opening datalog.txt");
}
i=0;
}
}
Any help would be much appreciated