Problems with AsyncTask

package com.example.helloandroid;

import java.io.File;

import android.os.AsyncTask;
import android.os.Environment;
import android.widget.Toast;

public class CheckTask extends AsyncTask<Void, Void, Boolean> {



protected Boolean doInBackground(Void... params) {
    while (true) {
        if (Environment.MEDIA_MOUNTED.equals(Environment
                .getExternalStorageState())) {
            // access external file
            String f = Environment.getExternalStorageDirectory()
                    + "/schedule.rtf";
            File s = new File(f);
            if (s.exists()) {
                return true;

            }

        }
    }

}

开发者_如何学Pythonprotected void onPostExecute(Boolean result) {
    if (result == true) {


         Toast.makeText(CheckTask.this, "Hello", Toast.LENGTH_SHORT).show();

    }
}
}

I keep getting the following error message: The method makeText(Context, CharSequence, int) in the type Toast is not applicable for the arguments (CheckTask, String, int)

I have tried searching some basic tutorials and they use Toast.makeText in the same way as above. I am not sure whats wrong.

Thank you.

It's because you are passing the CheckTask object instance in to makeText. You need to pass the instance/Context of your activity.

Is your AsyncTask an inner class of an actual activity? That is how the example below works and how I have always seen it done when looking at other people's code.

Here's a working example. Ignore the package name, I was having a play with creating a pedometer awhile back and just reused that project to do this.

package jm.pedometer;

import android.app.Activity;
import android.graphics.Typeface;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.Toast;

public class MainView extends Activity {
    Chronometer mChronometer;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mChronometer = (Chronometer)findViewById(R.id.Chronometer01);
    mChronometer.setTypeface(Typeface.createFromAsset(getAssets(), "fonts/digital_clock.ttf"));

    CheckTask testTask = new CheckTask();
    testTask.execute();
}


/*
 * This AsyncTask is an inner class within an Activity
 */
public class CheckTask extends AsyncTask<Void, Void, Boolean> {
protected Boolean doInBackground(Void... params) {
    return true;
}

protected void onPostExecute(Boolean result) {
    if (result == true) {
    Toast.makeText(MainView.this, "Hello", Toast.LENGTH_SHORT).show();
    }
    }
  }
}

Instead of passing CheckTask.this, just use this or this.getContext().