非常基本的android代码发布错误。 java.lang.RuntimeException：执行doInBackground（）时发生错误

Question

I made the program as simple as possible. But still the logcat says that an error occurred while execution doInBackground().

Here is my code

package com.example.basicasynctask;

import android.support.v7.app.AppCompatActivity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.Toast;


public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    new myFunc().execute();
}

private class myFunc extends AsyncTask<String,Void,Void> {

@Override
protected void onPreExecute() {
    super.onPreExecute();
    Toast.makeText(getApplicationContext(), "preExecute", Toast.LENGTH_SHORT).show();

}

@Override
protected Void doInBackground(String... arg0) {
     Toast.makeText(getApplicationContext(), "inBackground", Toast.LENGTH_SHORT).show();
         return null;
}

@Override
protected void onPostExecute(Void result) {
    super.onPostExecute(result);
    Toast.makeText(getApplicationContext(), "postExecute", Toast.LENGTH_SHORT).show();

}
}
}

Answer 1

If you want to show a Toast in doInBackground you can but you have to run it on a UI thread with runOnUIThread() .

If you can wait the end of the doInBackground process you will be able to show the Toast message in the onPostExecute method without running it on a UI thread