Question

我希望获得匹配的行，以＆＃34; a＆＃34;开头。并结束例如＆＃34; 140807＆＃34;在dir.txt中读取此行并将读取数据设置为我的TextView（如下所示：a152z140807）。我不知道为什么，但我的代码在TextView中设置了空白文本。

即使我改变了

data = inputLine;

为：

data = "something";

TextView中的文本设置为空白。提前谢谢。

TextView poleTextowe;

public void mButton (View view){

URLConnection nbpUrl;
String data = null;

try {
    nbpUrl = new URL("http://www.nbp.pl/Kursy/xml/dir.txt").openConnection();
    InputStream is = nbpUrl.getInputStream();
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    String inputLine;
    while ((inputLine = reader.readLine()) != null) {
        if (inputLine.startsWith("a") && inputLine.endsWith("140807")) {
            data = inputLine;
        }
    }
    is.close();

}catch(Exception e){
    e.printStackTrace();
}

poleTextowe = (TextView)findViewById(R.id.pole1);
poleTextowe.setText(data);

}

下面的xml文件：

<TextView
    android:text="@string/hello_world"
    android:id="@+id/pole1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />
<Button
    android:id="@+id/tekst"
    android:onClick="mButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/pole1"
    android:text="Click"/>

Answer 1

你可能有这个例外：

android.os.NetworkOnMainThreadException

Android不允许您在主（ui）线程上进行联网。例如，创建异步任务以执行网络任务。

Answer 2

这很简单，您的代码会引发异常，具体而言是android.os.NetworkOnMainThreadException。这意味着data保持null，并且没有显示任何内容。在AsyncTask或Thread

中运行它

这是一个非常常见的例子。将其设为Activity

中的内部类

public class MainActivity extends Activity {
    public void onCreate(Bundle b) {
        //usual stuff
    }

    public void doStuff() {
        new LongOperation().execute(); //run asynctask
    }

    private class LongOperation extends AsyncTask<String, Void, String> {
        @Override
        protected String doInBackground(String... params) {
            InputStream is = null;
            try {
                Log.d(TAG, "starting connection");
                URLConnection nbpUrl = new URL("http://www.nbp.pl/Kursy/xml/dir.txt").openConnection();
                is = nbpUrl.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(is));
                String inputLine;
                while ((inputLine = reader.readLine()) != null) {
                    if (inputLine.startsWith("a") && inputLine.endsWith("140807")) {
                        return inputLine; //because if the line's found, no need to look for other lines
                    }
                }
            }
            catch (Exception e) {
                e.printStackTrace();
            }
            finally {
                if (is != null) 
                    is.close(); //close inputstream in finally block, so it always gets closed
            }
            Log.d(TAG, "asynctask ran");
            return "NOT FOUND";
        }

        @Override
        protected void onPostExecute(String data) {
            poleTextowe = (TextView) findViewById(R.id.pole1);
            poleTextowe.setText(data);
        }

        @Override
        protected void onPreExecute() { }

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

在.txt文档中查找匹配的行

2 个答案: