Question

我有一段代码连接到服务器然后登录。当执行这两项任务（连接到服务器和登录）时，进展对话框出现。

final ProgressDialog pd = new ProgressDialog(getActivity());
pd.setIndeterminate(true);
pd.setCancelable(false);

// While connecting to the server, the dialog should say the following:
pd.setTitle("Connecting...");
pd.setMessage("Connecting to " + hostname + "...");

pd.show();

new AsyncTask<Void, Void, Void>() {

    @Override
    protected Void doInBackground(Void... params) {
        try {

            // First task is executed. Progress dialog should say "Connecting..."
            executeTask1();

            // When the first task (connecting to server) is ready, I want the title
            // and the message of the progress dialog to be changed into this:
            pd.setTitle("Logging in"); //// MARKED LINE, see below. ////
            pd.setMessage("Trying to log in to server...");

            // Second task is executed.
            executeTask2();

            // Shows a screen and dismisses the ProgressDialog.
            showScreen(ScreenConstant.LIST_RESIDENTS);
            pd.dismiss();
        }
        catch (Exception exc) { }
    }
}

但我遇到了两个问题：

执行MARKED LINE（见上文）时会引发RuntimeException：“只有创建视图层次结构的原始线程才能触及其视图”
登录任务从服务器获取响应，但此响应是异步的。

在执行连接尝试时，我希望ProgressDialog显示“正在连接...”文本。连接成功后，我希望在执行登录尝试时将进度对话框的文本更改为“登录...”。

现在我应该如何实现这个目标？

修改

请注意，executeTask2()会触发在不同主题中运行的任务;它向服务器发送一个登录请求，因此我需要等到该线程在准备就绪时发出信号。

Answer 1

任何触及UI的代码都应该在主线程上完成，因此您需要使用onProgressUpdate()和publishProgress()来实现此目的。

例如：

public void onProgressUpdate(Void... progress){
    super.onProgressUpdate(progress);
    pd.setTitle("Logging in");
    pd.setMessage("Trying to log in to server..."):
}

并在您的doInBackground()方法中：

executeTask1();
//task one finished, update UI
publishProgress();

除此之外，您应该忽略ProgressDialog中的onPostExecute()，因为这也会在主线程上执行

Answer 2

您需要在主线程中运行进度对话框，只有创建视图的线程才能更新或调用它，从而为您提供异常。

<强>样品：

    @Override
    protected Void doInBackground(Void... params) {
        try {

            // First task is executed. Progress dialog should say "Connecting..."
            executeTask1();

            // When the first task (connecting to server) is ready, I want the title
            // and the message of the progress dialog to be changed into this:
            getActivity().runOnUiThread(new Runnable() {

                @Override
                public void run() {
                    pd.setTitle("Logging in"); //// MARKED LINE, see below. ////
                    pd.setMessage("Trying to log in to server...");
                }
            });


            // Second task is executed.
            executeTask2();

            // Shows a screen and dismisses the ProgressDialog.
            showScreen(ScreenConstant.LIST_RESIDENTS);

            getActivity().runOnUiThread(new Runnable() {

                @Override
                public void run() {
                 pd.dismiss();  


                }
            });

        }
        catch (Exception exc) { }
    }

注意：

在主线程中运行的post execute Asynctask方法中删除对话框是明智的。

执行两个异步任务并更新AsyncTask消息

修改

2 个答案: