Android: File Reading - OutOfMemory Issue

问题

I am creating an app that involves reading in data from a file. The file is relatively large (1.8 MB) and is being read from an async thread in onCreate. The very first time the app is started up, it loads just fine. However, if you click the back button and then load it again, it runs out of memory and crashes (throwing the OutOfMemory error).

How do I get it to use the lowest amount of memory possible and/or free that memory when it is done?

File Reading Code (executed in the doInBackground() method of the async class):

public ArrayList<String> createDataList() {
    dataList = new ArrayList<String>();
    BufferedReader br = null;
    try {
        br = new BufferedReader(new InputStreamReader(getAssets().open(
                    "text.txt")));
        String data;
        while ((data = br.readLine()) != null) {
            dataList.add(data);
        }                           
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            br.close(); // stop reading
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    return dataList;
}

EDIT* Async Class:

private class loadData extends AsyncTask<Void, Void, ArrayList<String>> {

    @Override
    protected ArrayList<String> doInBackground(Void... arg0) {
        dataList = createDataList();
        return dataList;
    }

    protected void onPostExecute(ArrayList<String> result) {
        super.onPostExecute(result);
        // display first element in ArrayList in TextView as a test

    }

}

I have tried splitting up the file based on how I want to organize the data and store the data from each text file into a separate ArrayList but I had memory problems with that as well. I have also stored all of the data into one "master" ArrayList and then invoked a method on that "master" to add the data to the appropriate ArrayList (removing/clearing the data from the "master" as soon as it copied).

Any ideas on how to streamline and reduce memory impact?

EDIT**

Logcat:

That is from when you click the back button and then load the activity again. The following is just one of the messages produced (in verbose):

回答1:

First, make sure you don't have two copies of the data in memory. You can null out the reference to the old ArrayList before starting to create the new one, though you have to do that carefully -- calling ArrayList.clear() first would be more thorough.

Second, figure out how much memory that ArrayList is eating up by using a tool like hprof or Eclipse MAT. If it's using a ton of space, you may want to consider a more compact data representation.

So... from the code snippet, it looks like you're just reading a bunch of text strings in from a file, using a byte-to-char conversion. If the source material is plain UTF-8 (i.e. essentially ASCII), you've got a 2x expansion to UTF-16, plus allocation of the char[] object to hold it, plus the size of the String object that wraps that, plus the overhead of the entry in the ArrayList. Depending on how long an average string in the file is, this can be a significant multiple on your 1.8MB.

One way to avoid this would be to read the file into memory as byte[], scan it to figure out where each string starts, and just keep an array of integers with the start offset of each string. When you need string N, decode it from the byte[] into a String and return it. This reduces your overhead significantly. You could reduce it further by not loading the file and just reading individual strings out as needed (using a RandomAccessFile), but this may slow things down.

回答2:

You can try adding android:largeHeap="true" in your manifest but it is not supported in Android API-8. To my understanding, you are reading and storing the data onto heap memory, which is usually quite limited and its size depends on the device your running your app on.

You might also want to investigate here: android - out of memory

回答3:

Seems to be you might have a bit of trouble with the immutability of Strings .

Why don't you try changing your code so you use StringBuilder for instance? Of course, you'll have to change more than one thing but it would be similar enough to your code and wouldn't fill your memory up as fast.

来源：https://stackoverflow.com/questions/14763656/android-file-reading-outofmemory-issue