android - 从资产文件夹中读取文件

Question

我在文件夹中有一个大文本文件，assets我有一个按钮可以成功读取文件的下一行。但是，如果用户单击另一个按钮，我想阅读前一行。

将整个文件读入内存不是一种选择。文件行没有编号。

Answer 1

InputStream is = getResources().getAssets().open("abc.txt");
String result= convertStreamToString(is);

public static String convertStreamToString(InputStream is)
            throws IOException {
            Writer writer = new StringWriter();
        char[] buffer = new char[2048];
        try {
            Reader reader = new BufferedReader(new InputStreamReader(is,
                    "UTF-8"));
            int n;
            while ((n = reader.read(buffer)) != -1) {
                writer.write(buffer, 0, n);
            }
        } finally {
            is.close();
        }
        String text = writer.toString();
        return text;
}

Answer 2

如果您只需要跟踪前一行，则可以执行以下操作，在每次迭代中跟踪前一行（我假设您使用的是阅读器；对于本示例，BufferedReader）：

String previous = null, line; // null means no previous line
while (line = yourReader.readLine()) {
    // Do whatever with line
    // If you need the previous line, use:
    if (yourCondition) {
        if (previous != null) {
            // Do whatever with previous
        } else {
            // No previous line
        }
    }
    previous = line;
}

如果您需要跟踪前一行以上，您可能必须将其扩展为一个数组，但如果您的文件很大，您将在内存中保留大量内存 - 就像您阅读整个文件，一旦你到达最后一行。

在 Java 或 Android 中没有简单的方法来读取前一行，只有下一行（因为在文件 I/O 中更容易向前而不是向后）。

我能想到的另一种选择是保留一个线标记（从 0 开始），并且随着您通过线前进，增加它。然后，要倒退，您必须再次逐行读取文件，直到到达该行减一。如果您需要倒退，请转到该新行减一，依此类推。这很可能是一项繁重的操作，但会满足您的需求。

编辑：如果以上都不起作用，还有一种方法可以向后读取文件，您可以在其中通过向前迭代来找到前一行。只是一个替代的想法，但绝对不是一个容易实施的想法。

Answer 3

public class LoadFromAltLoc extends Activity {  

    //a handle to the application's resources  
    private Resources resources;  
    //a string to output the contents of the files to LogCat  
    private String output;  

    /** Called when the activity is first created. */  
    @Override  
    public void onCreate(Bundle savedInstanceState)  
    {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  

        //get the application's resources  
        resources = getResources();  

        try  
        {  
            //Load the file from the raw folder - don't forget to OMIT the extension  
            output = LoadFile("from_raw_folder", true);  
            //output to LogCat  
            Log.i("test", output);  
        }  
        catch (IOException e)  
        {  
            //display an error toast message  
            Toast toast = Toast.makeText(this, "File: not found!", Toast.LENGTH_LONG);  
            toast.show();  
        }  

        try  
        {  
            //Load the file from assets folder - don't forget to INCLUDE the extension  
            output = LoadFile("from_assets_folder.pdf", false);  
            //output to LogCat  
            Log.i("test", output);  
        }  
        catch (IOException e)  
        {  
            //display an error toast message  
            Toast toast = Toast.makeText(this, "File: not found!", Toast.LENGTH_LONG);  
            toast.show();  
        }  
    }  

    //load file from apps res/raw folder or Assets folder  
    public String LoadFile(String fileName, boolean loadFromRawFolder) throws IOException  
    {  
        //Create a InputStream to read the file into  
        InputStream iS;  

        if (loadFromRawFolder)  
        {  
            //get the resource id from the file name  
            int rID = resources.getIdentifier("fortyonepost.com.lfas:raw/"+fileName, null, null);  
            //get the file as a stream  
            iS = resources.openRawResource(rID);  
        }  
        else  
        {  
            //get the file as a stream  
            iS = resources.getAssets().open(fileName);  
        }  

        //create a buffer that has the same size as the InputStream  
        byte[] buffer = new byte[iS.available()];  
        //read the text file as a stream, into the buffer  
        iS.read(buffer);  
        //create a output stream to write the buffer into  
        ByteArrayOutputStream oS = new ByteArrayOutputStream();  
        //write this buffer to the output stream  
        oS.write(buffer);  
        //Close the Input and Output streams  
        oS.close();  
        iS.close();  

        //return the output stream as a String  
        return oS.toString();  
    }  
}