使用 URL 时无法解决符号错误

Question

class background_thread extends AsyncTask<String ,String , Boolean > {

    protected Boolean doInBackground(String... params) {

        String UR = "127.0.0.1/abc/index.php";
        try {
            URL url = new URL(UR);
        } catch(MalformedURLException e) {
            e.printStackTrace();
        }

        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    }

}

When I use the above code, in the HttpURLConnection the url turns red and Android Studio is showing an error can not resolve symbol url . What's wrong with the code?

Answer 1

I encountered the same problem. Just do:

import java.net.URL;

Answer 2

Put the line which is openning connection inside of try clause:

try {
    URL url = new URL(UR);
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();

    // Do something...

} catch (IOException e) {
    e.printStackTrace();
} finally {
    conn.disconnect();
}

It is because the valiable url is a local one which is valid only inside the try clause.

Or declair the url outside of the try clause:

URL url;
try {
    url = new URL(UR);
} catch (MalformedURLException e) {
    e.printStackTrace();
}

try {
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();

    // Do something...

} catch (IOException e) {
    e.printStackTrace();
} finally {
    conn.disconnect();
}

---

With Java 7+, we can use the AutoClosable feature:

URL url;
try {
    url = new URL(UR);
} catch(MalformedURLException e) {
    e.printStackTrace();
}

try (HttpURLConnection conn = (HttpURLConnection) url.openConnection())

    // Do something...

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

Answer 3

Sometimes you need a asimple 'gradlew clean'

"Click" on "Build"->"Clean Project" and that will perform a gradle clean

Or:

"Tools" -> "Android" -> "Sync Project with Gradle Files"

Answer 4

Adding

import java.net.MalformedURLException;

solve the missing resolve symbol.

You must of course have this too:

import java.net.URL;