我正在尝试显示一个ProgressBar。

我是Android初学者。

当我按下按钮时，任务应该在后台运行，但是它不会显示ProgressBar。

怎么了 我不明白。

请帮我！

主要活动：

package com.example.shikkok_services;

import java.util.ArrayList;

import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity {


    private Button btnThread,btntask;
    private ProgressDialog pd;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnThread=(Button)findViewById(R.id.btnStartThread);
        btntask=(Button)findViewById(R.id.btntsk);

        btntask.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {


                //start myTast

                new MyTask(MainActivity.this).execute();


            }
        });



    }

}

我的任务：

 package com.example.shikkok_services;

import android.app.Dialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class MyTask extends AsyncTask<Void, Integer, Void> {

    Context context;
    Handler handler;
    Dialog dialog;
    TextView txtprogrss;
    ProgressBar progress;
    Button btnCancel;

    MyTask(Context context, Handler handler){
        this.context=context;
        this.handler=handler;

    }

    MyTask(Context context){
      this.context=context;
      this.handler=handler;
    }

    @Override
    protected void onPreExecute() {

        super.onPreExecute();
        // create dialog
        dialog=new Dialog(context);
        dialog.setCancelable(true);
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        dialog.setContentView(R.layout.pogressdialog);
        txtprogrss=(TextView) dialog.findViewById(R.id.txtProgress);
        progress=(ProgressBar)dialog.findViewById(R.id.progressBar2);
        btnCancel=(Button)dialog.findViewById(R.id.btnProgress);

        btnCancel.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

                MyTask.this.cancel(true);
            }
        });


    }


    @Override
    protected Void doInBackground(Void... arg0) {


        for (int i = 0; i < 100; i++) {
            if(isCancelled()){
            break;
            }else{
            Log.e("In Background","current value;"+ i);
            publishProgress(i);

            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            }

        }

        return null;    
    }

    @Override
    protected void onProgressUpdate(Integer... values) {


        super.onProgressUpdate(values);


        progress.setProgress(values[0]);
        txtprogrss.setText("progress update"+ values[0]+"%");

    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);


        dialog.dismiss();
        Toast.makeText(context, "Finished", Toast.LENGTH_LONG).show();

    }





}