如何在Android Java中的for循环内使用AsyncTask

Question

Please help me, I'm trying to create random button change colors using AsyncTask class inside of a for cycle (for a future game) but I don't know why it doesn't work properly, when the "RUN" button is pressed apparently the cycle is executed only once instead of 20, because the other buttons change color only once. here is my code: (thanks)

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_vertical"
android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.mybuttons.MainActivity" >

    <Button
        android:id="@+id/btnOne"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/btnRun"
        android:layout_alignParentTop="true"
        android:text="BUTTON ONE" />

    <Button
        android:id="@+id/btnTwo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/btnOne"
        android:layout_below="@+id/btnOne"
        android:text="BUTTON TWO" />

    <Button
        android:id="@+id/btnThree"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/btnTwo"
        android:layout_below="@+id/btnTwo"
        android:text="BUTTON THREE" />

    <Button
        android:id="@+id/btnFour"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/btnThree"
        android:layout_below="@+id/btnThree"
        android:text="BUTTON FOUR" />

    <Button
        android:id="@+id/btnFive"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/btnFour"
        android:layout_below="@+id/btnFour"
        android:text="BUTTON FIVE" />

    <Button
        android:id="@+id/btnRun"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/btnFive"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="33dp"
        android:text="RUN" />

</RelativeLayout>

The code:

package com.myexercise;

import java.util.Random;

import android.app.Activity;
import android.graphics.Color;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity implements OnClickListener {

    Button myOne;
    Button myTwo;
    Button myThree;
    Button myFour;
    Button myFive;
    Button myRun;
    int wichOne;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myOne=(Button)findViewById(R.id.btnOne);
        myTwo=(Button)findViewById(R.id.btnTwo);
        myThree=(Button)findViewById(R.id.btnThree);
        myFour=(Button)findViewById(R.id.btnFour);
        myFive=(Button)findViewById(R.id.btnFive);
        myRun=(Button)findViewById(R.id.btnRun);
        myRun.setOnClickListener(this);
    }
    @Override
    public void onClick(View v) {
        for(int i=0;i<20;i++){
            System.out.println("i="+i);
            MyAsyncTask runner = new MyAsyncTask(); 
            String sleepTime = "500";
            int myRandom=new Random().nextInt(5);
            String thisButton = Integer.toString(myRandom);
            runner.execute(sleepTime, thisButton);
        }
    }
    class MyAsyncTask extends AsyncTask<String, String, String> {
        private String resp;
        @Override
        protected String doInBackground(String... params) {
            try {
                int time = Integer.parseInt(params[0]);  
                wichOne = Integer.parseInt(params[1]);
                Thread.sleep(time);
            } catch (InterruptedException e) {
                e.printStackTrace();
                resp = e.getMessage();
            } catch (Exception e) {
                e.printStackTrace();
                resp = e.getMessage();
            }
            return resp;
        }
        @Override
        protected void onPostExecute(String result) {
            myOne.setBackgroundColor(Color.LTGRAY);
            myTwo.setBackgroundColor(Color.LTGRAY);
            myThree.setBackgroundColor(Color.LTGRAY);
            myFour.setBackgroundColor(Color.LTGRAY);
            myFive.setBackgroundColor(Color.LTGRAY);
        }
        @Override
        protected void onPreExecute() {
            if(wichOne==0){
                myOne.setBackgroundColor(Color.YELLOW);
            }else{
                if(wichOne==1){
                    myTwo.setBackgroundColor(Color.BLUE);
                } else {
                    if(wichOne==2){
                        myThree.setBackgroundColor(Color.CYAN);
                    } else{
                        if(wichOne==3){
                            myFour.setBackgroundColor(Color.RED);
                        } else{
                            myFive.setBackgroundColor(Color.DKGRAY);
                        }
                    }
                }
            }
        }
    }
}

Answer 1

I don't know if this will solve your issue, but there is a big error in your Async.

You are attempting to read wichOne value in onPreExecute method while the value is defined in your onBackground!

You should use a constructor for your asynctask and pass arguments to it:

@Override
public void onClick(View v) {
    for(int i=0;i<20;i++){
        System.out.println("i="+i); 
        int myRandom=new Random().nextInt(5);
        MyAsyncTask runner = new MyAsyncTask(500, myRandom);
        runner.execute();
    }
}
class MyAsyncTask extends AsyncTask<String, String, String> {
    private String resp;

    private int mWichOne;
    private int mTime;

    public MyAsyncTask(int time, int wich) {
        mTime = time;
        mWichOne = wich;
    }

    @Override
    protected void onPreExecute() {
        switch (mWichOne) {
            case 0: // do whatever you want with the mWichOne value
        }
    }

    @Override
    protected String doInBackground(String... params) {
        try {
            Thread.sleep(mTime); // Why you are doing this???
        } catch (InterruptedException e) {
            e.printStackTrace();
            resp = e.getMessage();
        } catch (Exception e) {
            e.printStackTrace();
            resp = e.getMessage();
        }
        return resp;
    }
    @Override
    protected void onPostExecute(String result) {
        myOne.setBackgroundColor(Color.LTGRAY);
        myTwo.setBackgroundColor(Color.LTGRAY);
        myThree.setBackgroundColor(Color.LTGRAY);
        myFour.setBackgroundColor(Color.LTGRAY);
        myFive.setBackgroundColor(Color.LTGRAY);
    }
}