Android File I/O openFileInput() undefined

问题:

            package com.example.tictactoeshowgrid;

            import android.os.Bundle;
            import java.io.*;
            import android.widget.Toast;
            import android.content.*;

            import java.io.FileInputStream;
            import java.io.FileNotFoundException;
            import java.io.FileOutputStream;
            import java.io.IOException;
            import java.util.Date;

            import android.content.Context;

                public class ImportOBJ {

                protected void onCreate(String filename) {
                    try
                    {
                        FileInputStream fis = openFileInput(filename);
                        BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
                        String line = null, input="";
                        while ((line = reader.readLine()) != null)
                            input += line;
                        reader.close();
                        fis.close();
                        //toast("File successfully loaded.");
                        //return input;
                    }
                    catch (Exception ex)
                    {
                        //toast("Error loading file: " + ex.getLocalizedMessage());
                        //return "";
                    }
                }
            }

I am looking at an example of File I/O for Android. I am wondering why openFileInput is coming up with an error as being an undefined function. I was thinking that maybe I missed an import? If not then there must be some other problem.

Thanks in advance...

回答1:

for accessing openFileInput method in non Activity class you will need to pass Activity Context to it by sending Context using parametrized method or using ImportOBJ class constructor as:

protected void onCreate(String filename,Context context) {
   try
     {
         FileInputStream fis = context.openFileInput(filename);  
         //...your code here...      
     }
   catch (Exception ex)
     {

     }
}

and from your Activity pass context as:

ImportOBJ obj_import=new ImportOBJ();
obj_import.onCreate(<File_Name_Here>,Your_Current_Activity_Name.this);

回答2:

If error is :

The method openFileInput(String) is undefined for the type ...

You have to use openFileInput in a Context.For example an Activity is a Context.So if you cahnge your class to this,error must be solve:

public class ImportOBJ extends Activity{
.
.
.

}

You can see What is Context in Android? for more details on Context.