Question

有人可以看看这段代码吗，让我知道我做错了什么？这是一个简单的函数，它将一个字符串作为参数，将其用作文件名，并在其末尾添加“.txt”。

该函数检查文件是否存在，如果不存在则创建它，然后将两行文本写入文件。一切似乎都在工作，文件在SD卡上成功创建。但是，完成所有操作后，文件为空（并且大小为0字节）。

我怀疑这是显而易见的，我忽视了。

public void writeFile(String fileName) {
    String myPath = new File(Environment.getExternalStorageDirectory(), "SubFolderName");
    myPath.mkdirs();

    File file = new File(myPath, fileName+".txt");

    try {
        if (!file.exists()) {
            if (!file.createNewFile()) {
                Toast.makeText(this, "Error Creating File", Toast.LENGTH_LONG).show();
                return;
            }
        }

        OutputStreamWriter writer = new OutputStreamWriter(openFileOutput(file.getName(), Context.MODE_PRIVATE));
        writer.append("First line").append('\n');
        writer.append("Second line").append('\n');

        writer.close();
    }
    catch (IOException e) {
        // Do whatever
    }
}

Answer 1

您好我会告诉您我使用的完整代码，效果很好。我不使用

 new OutputStreamWriter()

我用

new BufferedWriter()

这是我的代码段

public void writeToFile(Context context, String fileName, String data) {

    Writer mwriter;

    File root = Environment.getExternalStorageDirectory();
    File dir = new File(root.getAbsolutePath() + File.separator + "myFolder");

    if (!dir.isDirectory()) {
        dir.mkdir();
    }

    try {
        if (!dir.isDirectory()) {
            throw new IOException(
                "Unable to create directory myFolder. SD card mounted?");
        }
        File outputFile = new File(dir, fileName);
        mwriter = new BufferedWriter(new FileWriter(outputFile));
        mwriter.write(data); // DATA WRITE TO FILE
        Toast.makeText(context.getApplicationContext(),
            "successfully saved to: " + outputFile.getAbsolutePath(), Toast.LENGTH_LONG).show();
        mwriter.close();
    } catch (IOException e) {
        Log.w("write log", e.getMessage(), e);
        Toast.makeText(context, e.getMessage() + " Unable to write to external storage.",Toast.LENGTH_LONG).show();
        }
}

-- Original Code --

Answer 2

那个人需要一段时间才能找到答案。 javadocs here让我走上正轨。它说：

Parameters
name    The name of the file to open; can not contain path separators.
mode    Operating mode. Use 0 or MODE_PRIVATE for the default operation, MODE_APPEND to append to an existing file, MODE_WORLD_READABLE and MODE_WORLD_WRITEABLE to control permissions.

如果该文件不存在，则会创建该文件，但该文件是在私有应用空间中创建的。您可以使用File.createNewFile()在SD卡上的某个位置创建文件，但是当您执行context.openFileOutput()时，它会在私有应用空间中创建始终私有文件。

编辑：这是我的代码。我通过编写和读取行来扩展你的方法并打印我对logcat的所有内容。

<pre>
    public void writeFile(String fileName) {
    try {
        OutputStreamWriter writer = new OutputStreamWriter(
                getContext().openFileOutput(fileName + ".txt", Context.MODE_PRIVATE));
        writer.append("First line").append('\n');
        writer.append("Second line").append('\n');

        writer.close();
    }
    catch (IOException e) {
        Log.e("STACKOVERFLOW", e.getMessage(), e);
        return;
        // Do whatever
    }

    // Now read the file
    try {
        BufferedReader is = new BufferedReader(
                new InputStreamReader(
                        getContext().openFileInput(fileName + ".txt")));
        for(String line = is.readLine(); line != null; line = is.readLine())
            Log.d("STACKOVERFLOW", line);

        is.close();
    } catch (IOException e) {
        Log.e("STACKOVERFLOW", e.getMessage(), e);
        return;
        // Do whatever
    }
}

Answer 3

在Context.MODE_PRIVATE

中将模式从Context.MODE_APPEND更改为openFileOutput()

MODE_APPEND

MODE_PRIVATE

而不是

OutputStreamWriter writer = new OutputStreamWriter(openFileOutput(file.getName(), Context.MODE_PRIVATE));

使用

OutputStreamWriter writer = new OutputStreamWriter(openFileOutput(file.getName(), Context.MODE_APPEND));

更新：

<强> 1

FileOutputStream osr = new FileOutputStream(file.getName(), true); // this will set append flag to true

OutputStreamWriter writer = new OutputStreamWriter(osr);
BufferedWriter fbw = new BufferedWriter(writer);
            fbw.write("First line");
            fbw.newLine();
            fbw.write("Second line");
            fbw.newLine();
            fbw.close();

或2。

private void writeFileToInternalStorage() {
          FileOutputStream osr = new FileOutputStream(file.getName(), true); // this will set append flag to true
          String eol = System.getProperty("line.separator");
          BufferedWriter fbw = null;
          try {
              OutputStreamWriter writer = new OutputStreamWriter(osr);
              fbw = new BufferedWriter(writer);
              fbw.write("First line" + eol);
              fbw.write("Second line" + eol);           

          } catch (Exception e) {
              e.printStackTrace();
          } finally {
            if (fbw != null) {
            try {
                fbw.close();
            } catch (IOException e) {
              e.printStackTrace();
            }
            }
          }
        }

我可以创建文件但不能写入它

3 个答案: