我有很多谷歌，阅读 javadoc，以及搜索不同的论坛，包括这个阅读问题，但没有找到我问题的正确答案。下面的代码片段工作正常，但我想确切地知道在 android 中用于读/写文件的函数。可以使用OutputStream、FileOutputSteam.write() 写入内部存储，另一种是使用OutputStreamWriter(FileOutputSteam).write()，再使用BufferedWriter(OutputStreamWriter).write()，最后使用PrintWriter.write()。
对于 InputStream 案例，是否使用 InputStream、FileInputSteam.read()、InputSreamReader(FileInputStream).read()、BufferedReader(InputStreamReader) 也是如此。
我想知道哪种方法是最好的方法。请帮我解决这个问题。
public class MainActivity extends Activity {
private static final String TAG = MainActivity.class.getName();
private static final String FILENAME = "students.txt";
private EditText stdId;
private Button Insert;
private Button Search;
private Button Update;
private Button Delete;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final String TAG = MainActivity.class.getName(); //output: com.fyp2.testapp.MainActivity
//value used for insert/delete/search
stdId = (EditText) findViewById(R.id.editTxtId);
//insert value in application sandbox file
Insert = (Button) findViewById(R.id.btnInsert);
Insert.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String IdToInsert = stdId.getText().toString().trim();
if(IdToInsert.length() > 0) {
myInsertFunc(IdToInsert);
}
else {
Toast.makeText(getApplicationContext(), "Id cannot be null!", Toast.LENGTH_SHORT).show();
stdId.requestFocus();
}
}
});
//search value from application sandbox file
Search = (Button) findViewById(R.id.btnSearch);
Search.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String IdToSearch = stdId.getText().toString().trim();
if(IdToSearch.length() > 0) {
mySearchFunc(IdToSearch);
}
else {
Toast.makeText(getApplicationContext(), "Id cannot be null!", Toast.LENGTH_SHORT).show();
stdId.requestFocus();
}
}
});
//delete value from application sandbox file
Delete = (Button) findViewById(R.id.btnDelete);
Delete.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String IdToDelete = stdId.getText().toString().trim();
if(IdToDelete.length() > 0) {
myDeleteFunc(IdToDelete);
}
else {
Toast.makeText(getApplicationContext(), "Id cannot be null!", Toast.LENGTH_SHORT).show();
stdId.requestFocus();
}
}
});
}
//function to insert
private void myInsertFunc(String data) {
//If student id already exist don't write it again -> Not handled at the moment
//Other exceptions may not have been handled properly
try {
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput(FILENAME, Context.MODE_APPEND));
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
bufferedWriter.append(data);
bufferedWriter.newLine();
Toast.makeText(getApplicationContext(), "Student ID: " + data + " Inserted Successfully!", Toast.LENGTH_SHORT).show();
bufferedWriter.close();
outputStreamWriter.close();
}
catch (IOException e) {
Log.e(TAG, "File write failed: " + e.toString());
}
}
//function to search
private void mySearchFunc(String data) {
//Id id not found show toast to user -> Not handled at the moment
try {
InputStream inputStream = openFileInput(FILENAME);
if (inputStream != null) {
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
String receiveString = "";
while ((receiveString = bufferedReader.readLine()) != null) {
if(receiveString.contains(data))
{
Toast.makeText(getApplicationContext(), "Found Student ID: " + data , Toast.LENGTH_SHORT).show();
break;
}
}
bufferedReader.close();
inputStream.close();
}
}
catch (FileNotFoundException e) {
Log.e(TAG, "File not found: " + e.toString());
} catch (IOException e) {
Log.e(TAG, "Can not read file: " + e.toString());
}
}
private void myDeleteFunc(String data) {
/* I have found a solution to delete a specific line from the file.
* But the problem is that it needs to scan the whole file line by line and copy the file contents that not matches the string to temp file.
* This solution can reduce the effeciency. Consider search 20,000 records in a file.
* Need to work around on it.
*/
}
private void myUpdateFunc(String data) {
/* Same goes to the update process...
* Need to scan all records and copy content in temp file and put the updated data in that file.
* Need to work around on this issue too...
*/
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}