检查Android中的文件是否为空 [英] Checking if a File is Blank in Android

问题描述

这是我的代码示例.该代码很长，仅用于测试文件是否为空，如果不是，则将其写入.无论哪种方式，行 if(！(data.equals("))&&！(data.equals(null)))都不起作用，即使文件为空，它仍然会通过警报.

  FileInputStream fIn = null;字符串数据= null; InputStreamReader isr = null;尝试{char [] inputBuffer = new char [1024];fIn = openFileInput("test.txt");isr =新的InputStreamReader(fIn);isr.read(inputBuffer);数据=新的String(inputBuffer);isr.close();fIn.close();} catch(IOException e){}//这是检查从文件输入的数据是否为空if(！(data.equals("))&&！(data.equals(null))){AlertDialog.Builder builder =新的AlertDialog.Builder(Main.this);builder.setMessage(清除文件吗?" +'\ n'+此操作无法撤消.").setCancelable(false).setPositiveButton(是"，新的DialogInterface.OnClickListener(){public void onClick(DialogInterface dialog，int id){我们的EditText =(EditText)findViewById(R.id.txtWrite);FileOutputStream fOut = null;OutputStreamWriter osw = null;尝试{fOut = openFileOutput("test.txt"，Context.MODE_PRIVATE);osw =新的OutputStreamWriter(fOut);osw.write(");osw.close();fOut.close();we.setText(");} catch(Exception e){}}}).setNegativeButton("No"，新的DialogInterface.OnClickListener(){public void onClick(DialogInterface dialog，int id){dialog.cancel();}});AlertDialog alert = builder.create();alert.show();} 

此外，如果有人可以简化这段代码，那就太好了！

解决方案

如果文件为空(无内容)，则其长度为0.如果文件不存在，则长度也返回0；否则，该长度返回0.如果这是必要的区别，则可以使用 exists 方法检查文件是否存在.

 文件f = getFileStreamPath("test.txt");如果(f.length()== 0){//为空或不存在} 别的 {//存在且不为空} 

当前方法无法工作，因为 inputBuffer 是一个1024个字符的数组，并且从该缓冲区创建的字符串也将具有1024个字符，而与从文件中成功读取了多少个字符无关./p>

This is my code sample. The code is pretty long just to test if a file is blank and then if it isn't, write onto it. Either way, the line if (!(data.equals("")) && !(data.equals(null))) doesn't work and even when the file is blank, it still goes through the Alert.

FileInputStream fIn = null;String data = null;InputStreamReader isr = null;
try{
    char[] inputBuffer = new char[1024];
    fIn = openFileInput("test.txt");
    isr = new InputStreamReader(fIn);
    isr.read(inputBuffer);
    data = new String(inputBuffer);
    isr.close();
    fIn.close();
}catch(IOException e){}

// this is the check for if the data inputted from the file is NOT blank
if (!(data.equals("")) && !(data.equals(null)))
{
    AlertDialog.Builder builder = new AlertDialog.Builder(Main.this);
    builder.setMessage("Clear your file?" + '\n' + "This cannot be undone.")
    .setCancelable(false)
    .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            EditText we = (EditText)findViewById(R.id.txtWrite);
            FileOutputStream fOut = null;

            OutputStreamWriter osw = null;
            try{
                fOut = openFileOutput("test.txt", Context.MODE_PRIVATE);
                osw = new OutputStreamWriter(fOut);
                osw.write("");
                osw.close();
                fOut.close();
                we.setText("");
            }catch(Exception e){}
        }
    })
    .setNegativeButton("No", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            dialog.cancel();
        }
    });
    AlertDialog alert = builder.create();
    alert.show();
}

Also, if anyone has a way of shorting up this code, I would be greatful!

解决方案

If a file is blank (has no contents) its length is 0. The length returns also 0 if it doesn't exist; if this is a necessary distinction you can check if the file exists with the exists method.

File f = getFileStreamPath("test.txt");
if (f.length() == 0) {
    // empty or doesn't exist
} else {
    // exists and is not empty
}

The current approach fails to work because inputBuffer is an array of 1024 chars, and a strings created from it will also have 1024 chars, independently of how many chars were successfully read from the file.

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