Java/Android 在运行新方法之前等待线程完成

Question

我有一个 android 应用程序(用 java 编写)，它有两个按钮(连接 和请求数据)。

单击每个按钮时，都会执行一个任务，并且会出现一个进度对话框，以显示任务完成了多少。

为了显示进度对话框，当每个按钮被点击时，任务在一个线程上运行。

connect 按钮只有一项任务 - 在线程上运行。但是，request data 按钮执行两个任务 - 线程上的第一个任务类似于连接按钮，还有第二个任务，refreshInfo()，它必须在线程上的第一个任务 progThread 已完成。

private Button connectButton;
private Button requestDataButton;

private ProgressDialog connectionDialog;
private ProgressDialog requestDataDialog;

private ProgressThread progThread;

private int currentDialog;

public void connectClick(View view)      //When the connect button is clicked
{
    performAction(1);   //Run the thread to perform the action
}

public void requestDownloadClick(View view)   //When the request data button is clicked
{
    performAction(2);    //Run the thread to perform the action

    refreshInfo();    //Do something else
}

private void performAction(int type)
{
    currentDialog = type;

    showDialog(type);

    try 
    {
        progThread.join();
    } 
    catch (InterruptedException e) 
    {
        e.printStackTrace();
    }
}

这里的关键方法是performAction(int type)。我基本上不希望此方法在 progThread 完成运行之前完成。

如您所见，我已尝试使用 progThread.join() 来阻止该方法在 progThread 完成运行之前继续执行，但是作为 progThread 涉及显示进度对话框，运行progThread.join() 似乎会阻止显示进度对话框，就像当前您单击按钮，第一个任务正在执行，但对话框只在最后闪烁。

谁能想出一种方法来运行线程，正常显示进度对话框，然后运行第二种方法(如果有的话)。

我在下面包含了线程代码，以备不时之需。

private class ProgressThread extends Thread 
{   
    final static int DONE = 0;
    final static int RUNNING = 1;   // Class constants defining state of the thread

    private Handler progressHandler;
    int mState;
    int total;

    ProgressThread(Handler _handler)    // Constructor with an argument that specifies Handler on main thread to which messages will be sent by this thread.
    {
        progressHandler = _handler;
    }

    public void run()    // Invoked automatically when the Thread starts.  
    {
        mState = RUNNING;   

        updateProgressBar();

        connectButton = (Button) findViewById(R.id.btnConnect);
        requestDataButton = (Button) findViewById(R.id.btnRequestDownload);

        while (mState == RUNNING) 
        {
            if (currentDialog == 1)
            {
                try
                { 
                    doSomething();

                    if (something)
                    {
                        setState(DONE);

                        total = 100;

                        updateProgressBar();

                        removeDialog(1);

                        connectButton.setEnabled(false);
                    }
                    else
                    {
                        total = total + 20;

                        if (something has reached a limit)
                        {
                            setState(DONE);

                            total = 0;

                            updateProgressBar();

                            removeDialog(1); 
                        }
                    }

                    updateProgressBar();
                }
                catch (Exception e)
                {

                }
            }

            if (currentDialog == 2)
            {
                try
                {
                    doSomething();

                    total = 10;

                    updateProgressBar();

                    doSomething();

                    total = 70;

                    updateProgressBar();

                    if (something)  //If the download info has not been got
                    {
                        setState(DONE);

                        total = 0;

                        updateProgressBar();

                        removeDialog(2);

                        runOnUiThread(new Runnable()
                        {
                            public void run() 
                            {
                                connectButton.setEnabled(true);

                                requestDataButton.setEnabled(true);
                            }                               
                        });  
                    } 
                    else
                    {
                        total = 100;

                        updateProgressBar();

                        setState(DONE);

                        removeDialog(2);

                        runOnUiThread(new Runnable()
                        {
                            public void run() 
                            {
                                requestDataButton.setEnabled(false);
                            }                               
                         }); 
                     }
                }
                catch (Exception e)
                {
                    removeDialog(2);

                    setState(DONE);

                    runOnUiThread(new Runnable()
                    {
                        public void run() 
                        {
                            connectButton.setEnabled(true);

                            requestDataButton.setEnabled(true);
                        }                               
                    });  
                }
            }
        }
    }

    // Set current state of thread (use state=ProgressThread.DONE to stop thread)
    public void setState(int state) 
    {
        mState = state;
    }

    public void updateProgressBar()
    {
        Message msg = progressHandler.obtainMessage();   // Send message (with current value of  total as data) to Handler on UI thread so that it can update the progress bar

        Bundle b = new Bundle();

        b.putInt("total", total);

        msg.setData(b);

        progressHandler.sendMessage(msg);
    }
}

final Handler handler = new Handler()     // Handler on the main (UI) thread that will receive messages from the second thread and update the progress.
{
    public void handleMessage(Message msg) 
    {
        int total = msg.getData().getInt("total");             // Get the current value of the variable total from the message data and update the progress bar

        switch (currentDialog)
        {
        case 1 : 
            connectionDialog.setProgress(total);
            break;

        case 2 : 
            requestDataDialog.setProgress(total);
            break;
        }
    }
};

protected Dialog onCreateDialog(int id) 
{   
    switch (currentDialog)
    {
    case 1 :
        connectionDialog = new ProgressDialog(this);

        connectionDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);

        connectionDialog.setMax(100);

        connectionDialog.setProgress(0);

        connectionDialog.setMessage("Connecting To The Device");

        progThread = new ProgressThread(handler);

        progThread.start();

        return connectionDialog;

    case 2 :
        requestDataDialog = new ProgressDialog(this);

        requestDataDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);

        requestDataDialog.setMax(100);

        requestDataDialog.setProgress(0);

        requestDataDialog.setMessage("Requesting Download Data");

        progThread = new ProgressThread(handler);

        progThread.start();

        return requestDataDialog;

    default : 
        return null;
    }
}

Answer 1

Android API 提供了一个 AsyncTask class其中有两个方法 doInBackground 和 onPostExecute。你必须重写它们，在 doInBackground 中做任何你必须做的事情，当工作完成时 onPostExecute 回调将运行。还有一个 onProgressUpdate 回调，这正是您所需要的。