Android学习之——并发编程：AsyncTask和UI线程

((Button)findViewById(R.id.start)).setOnClickListener(
    new View.OnClickListener(){
        @Override public void onClick(View v){
            new AsyncInitGame(root, bg, game, msg).execute("basic");
        }
    }
);//注：该文中的代码并不全面，只是为了阐述AsyncTask

public class AsyncDBReq extends AsyncTask<PreparedStatement, Void, ResultSet>
{
    @Override protected ResultSet doInBackground(PreparedStatement...q){
        //implementation.....
    }
    @Override protected onPostExecute(ResultSet result){
        //implementation
    }
}
public class AsyncHttpReq extends AsyncTask<HttpRequest, Void, HttpResponse>
{
    @Override protected HeepResponse doInBackground(HttpRequest.....req){
        //implementaion.....
    }
    @Override protected void onPostExecute(HttpResponse result){
        //implementaion
    }
}

//易犯错误一、
//....some clas
int mCOunt;
public void initButton1(Button button){
    mCOunt = 0;
    button.setonClickListener(
        new View.OnClickListener(){
            @SuppressWarnings("unchecked")
            @Override public void onCLick(View v){
                new AsyncTask<Void, Void, Void>(){
                    @Override protected Void doInBackground(Void...args){
                        mCount++; //!!! not thread safe!!
                        return null;
                    }
                }.execute();
            }});
}

//易犯错误二、
public void initButton(Button button, final Map<String, String> vals){
    button.setOnClickListener(
        new View.OnClickListener(){
            @Override public void onClick(View v){
                new AsyncTask<Map<String, String>, Void, Void>(){
                    @Override protected Void doInBackground(Map<String,String>...params){
                        //implementation, uses the params Map
                    }
                }.execute(vals);
                vals.clear();//this is not thread safe!!!!
            }});
}

public class AsyncTaskDemoWithProgress extends Activity{
    private final class AsyncInit extends AsyncTask<String, Integer, String> implements Game.InitProgressLIstener
    {
        private final View root;
        private final Game game;
        private final TextView message;
        private final Drawable bg;
 
        public AsyncInit(View root, Drawable bg, Game game, TextView msg){
        this.root = root;
        this.bg = bg;
        this.game = game;
        this.message = msg;
        }
        //run on the UI thread 
        //1. 当UI线程调用任务的execute方法时，会首先调用该方法
        @Override protected void onPreExecute()
        {
            if(0 >= mInFlight++){
                root.setBackgroundResouce(R.anim.dots);
                ((AnimationDrawable)root.getBackground()).start();
            }
        }
        //runs on the UI thread
        //3. 当doInBackground方法完成时，就删除背景线程，再在UI线程中调用onPostExecute方法。
        @Override protected void onPostExecute(String msg){
            if(0 >= --mInFlight){
                ((AndimationDrawable)root.getBackground()).stop();
                root.setBackgroundDrawable(bg);
            }
            message.setText(msg);
        }
        //runs on its own thread
        //2. 在onPreExecute方法完成后AsyncTask创建新的背景线程，并发执行doInBackground方法。
        @Override protected String doInBackground(String... args){
            return (1 != args.length) || (null == args[0])) ? null : game.initialize(args[0]);
        }
        //runs on its UI thread 
        @Override protected void onProgressUpdate(Integer... vals){
            updateProgressBar(vals[0].intValue());
        }
        //runs on the UI thread
        @Override public void onInitProgress(int pctComlete){
            //为了正确地给UI线程发布进程状态，onInitProgress调用的是AsyncTask的publicProgress。
            //AsyncTask处理UI线程的publicProgress调度细节，从而onProgressUpdate可以安全地使用View方法。
            publicProgress(Integer.valueOf(pctComplete));
        }
    }
    int mInFlight,mComplete;
    /** @see android.app.Activity#onCreate(android.os.Bundle) */
    @Override public void onCreate(Bundle state){
        super.onCreate(state);
        setContentView(R.layout.asyncdemoprogress);
        final View root = findViewById(R.id.root);
        final Drawable bg = root.getBackground();
        final TextView msg = ((TextView)findViewById(R.id.msg));
        final Game game = Game.newGame();
        ((Button)findViewById(R.id.start)).setOnClickListener(
            new View.OnClickListener(){
            @Override public void onCLick(View v){
                mComplete=0;
                new AsyncInit(root, bg, game, msg).execute("basic");
            }});
    }
 
    void updateProgressBar(int progress){
        int p = progress;
        if(mComplete < p){
            mComplete = p;
            (ProgressBar)findViewById(R.id.progress)).setprogress(p);
        }
    }
}