Question

我正在尝试从我的Dropbox读取一个在线txt文件，并将其内容放入带有Asynctask的字符串中，但我无法设法返回我的字符串。

我的代码：

new LongOperation().execute("");
}
private class LongOperation extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {
        String path ="https://dl.dropboxusercontent.com/u/29289946/PCGAMEDONWLOADER/Slots/All%20Games/Rows_available/link2.txt";
        URL u = null;
        try {
            u = new URL(path);
            HttpURLConnection c = (HttpURLConnection) u.openConnection();
            c.setRequestMethod("GET");
            c.connect();
            InputStream in = c.getInputStream();
            final ByteArrayOutputStream bo = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            in.read(buffer); // Read from Buffer.
            bo.write(buffer); // Write Into Buffer.

            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    String album = bo.toString();


                    try {
                        bo.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            });

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (ProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return album;
    }

    @Override
    protected void onPostExecute(String result) {
        TextView txt = (TextView) findViewById(R.id.loadingtext);
        txt.setText("Executed"); // txt.setText(result);
        // might want to change "executed" for the returned string passed
        // into onPostExecute() but that is upto you
    }

    @Override
    protected void onPreExecute() {}

    @Override
    protected void onProgressUpdate(Void... values) {}
}
}

现在eclipse强调＆＃34;专辑＆＃34;接下来回来，所以我不能在进一步的操作中使用它。

感谢您的帮助。

Answer 1

为什么运行UI线程将数据分配给字符串...您可以在线程中使用它。

只需在您的doInBackground方法（）中执行：

 bo.write(buffer); // Write Into Buffer.
 String album = bo.toString();
 return album;

这里你的主要问题是你在runInMainThread（）方法中本地定义了你的String变量。然后你如何进入周边地区。如果您不想更改您的程序，那么只需将全局字符串定义为：

 public String doInBackGround()String...params){
 String album = "";
 .....
 ....

将值放在任何位置......例如album=bo.toString();并返回....

Answer 2

您在此功能中初始化了album：

runOnUiThread(new Runnable() {
            @Override
            public void run() {
                String album = bo.toString();


                try {
                    bo.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });

因此它仅适用于此范围。您可以通过检查Eclipse实际显示的错误来看到这一点。

Answer 3

这是因为你在runOnUiThread中声明了你的专辑字符串，所以在它之外就不会知道它。尝试在onPostExecute中声明它，如下所示：

private class LongOperation extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {
        String path ="https://dl.dropboxusercontent.com/u/29289946/PCGAMEDONWLOADER/Slots/All%20Games/Rows_available/link2.txt";
        URL u = null;
//Declare it here as final
final String album=null;
        try {
            u = new URL(path);
            HttpURLConnection c = (HttpURLConnection) u.openConnection();
            c.setRequestMethod("GET");
            c.connect();
            InputStream in = c.getInputStream();
            final ByteArrayOutputStream bo = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            in.read(buffer); // Read from Buffer.
            bo.write(buffer); // Write Into Buffer.

            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                   album = bo.toString();


                    try {
                        bo.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            });

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (ProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return album;
    }

    @Override
    protected void onPostExecute(String result) {
        TextView txt = (TextView) findViewById(R.id.loadingtext);
        txt.setText("Executed"); // txt.setText(result);
        // might want to change "executed" for the returned string passed
        // into onPostExecute() but that is upto you
    }

    @Override
    protected void onPreExecute() {}

    @Override
    protected void onProgressUpdate(Void... values) {}
}

为什么我不能从AsyncTask返回一个字符串？

3 个答案: