Android studio，打开一个文件，连续写入然后关闭

Question

I have code that is generating data every second and displaying onscreen. This all works fine but I want to create a log file of all the data to analyze later.

I can open/write/close a file each time data is created but I am unsure of how much processing power this is using as it is continually opening and closing the file

  String data= reading1","+reading2+","+time +"/n";
        try {
            FileOutputStream out = openFileOutput("data.csv", Context.MODE_PRIVATE);
            out.write(data.getBytes());
            out.close();
        } catch (Exception e) {
            e.printStackTrace();

I would prefer to have the file open when the start button is clicked.

if ( v.getId() == R.id.start ){
                // checks which button is clicked
                Log.d("dennis", "Scan working"); //logs the text
                // open a file
                try {
                    FileOutputStream out = openFileOutput("data.csv", Context.MODE_PRIVATE);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }

but when it comes to closing the file, no options for .close() appear when out is typed

if ( v.getId() == R.id.stop ){
                // checks which button is clicked

                out. // no valid options appear
                messageValue.setText(R.string.stopButtonText);// changes the hallo world text
                readNoRead=false;

            }

Does all the open/write/close need to be together or is it possible to

***open file***
-----
Cycle through all the data
-----
***Close file***

Answer 1

It is definitely possible to open, process and close a file all in one block without closing the file.

Your out variable is not showing any method suggestions because it has not been defined in that block. Change the line

FileOutputStream out = openFileOutput("data.csv", CONTEXT.MODE_PRIVATE);

to

out = openFileOutput("data.csv", CONTEXT.MODE_PRIVATE); 

and then add FileOutputStream out; to a line above the first if statement (outside of the block).

You may want to also look into 'try-catch-finally', or 'try with resources' as options for closing files in a try-catch block.

Answer 2

You should store a link to your FileOutputStream on top level in your class.

Example to your code:

FileOutputStream out;

void clickStart() {
    if (v.getId() == R.id.start){
        // checks which button is clicked
        Log.d("dennis", "Scan working"); //logs the text
        // open a file
        try {
            out = openFileOutput("data.csv", Context.MODE_PRIVATE);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
}

void writeData() {
    String data= reading1+","+reading2+","+time +"/n";
    try {
        out.write(data.getBytes());
    } catch (IOException e) {
        e.printStackTrace();
    }
}

void clickStop() {
    if (v.getId() == R.id.stop) {
        try {
            out.close();
        } catch(IOException e) {
            e.printStackTrace();
        }
        messageValue.setText(R.string.stopButtonText);// changes the hello world text
            readNoRead=false;
        }
}