Question

我希望在Log中显示URL的内容。但问题是这段代码没有将任何数据存储到onCreate方法的字符串变量 result 中，而不显示在日志中。

有什么建议吗？

public class DownloadTask extends AsyncTask<String,Void,String>
{

    @Override
    protected String doInBackground(String... urls) {
        String result = "";
        URL url;
        HttpURLConnection urlConnection = null;

        try{
            url = new URL(urls[0]);
            urlConnection = (HttpURLConnection) url.openConnection();
            InputStream in = urlConnection.getInputStream();
            InputStreamReader reader = new InputStreamReader(in);
            int data = reader.read();

            while(data!=-1)
            {
                char current = (char) data ;
                result+=result;
                data=reader.read();

            }
            return result;
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return null;
    }
}
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Log.i("Success","Till here worked");
    DownloadTask task = new DownloadTask();
    String result=" ";
    Log.i("Success","Till here worked");
    try {
        Log.i("Success","Till here worked");
        result = task.execute("https://www.google.com").get();
        Log.i("Success","Till here worked");
        Log.i("Content of URL : ",result);
        Log.i("Failure","No result before this");
    } catch (Exception e) {
        e.printStackTrace();
    }


}

Answer 1

您错过了异步执行的行为。DownloadTask将在单独的线程上启动，MainThread将按顺序运行代码。所以这样result每次都会为空。

所以onPostExecute() AsyncTask内的内容也是如此。了解AsyncTask的工作情况。

public class DownloadTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {
        String result = "";
        URL url;
        HttpURLConnection urlConnection = null;
        try {
            url = new URL(urls[0]);
            urlConnection = (HttpURLConnection) url.openConnection();
            InputStream in = urlConnection.getInputStream();
            InputStreamReader reader = new InputStreamReader(in);
            int data = reader.read();

            while (data != -1) {
                char current = (char) data;
                result += result;
                data = reader.read();

            }
            return result;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        if (result != null) {
            Log.i("Content of URL : ", result);
            // USe the result for further process here 
        } else {
            Log.i("Failure", "No result");
        }
    }
}
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    DownloadTask task = new DownloadTask();
     task.execute("https://www.google.com");
}

Answer 2

使用排球库从网址获取内容。

无法将URL的内容存储在变量字符串中

2 个答案: