Java从URL获取Android TextView中的JSON

Question

我想从Android Studio的文本视图中显示的php获取JSON响应。我现在有了这样的代码，但它不起作用。据我所知，当应用程序打开时，它甚至没有运行

public class MainActivity extends Activity {

private SQLiteHandler db;
private SessionManager session;

private String readAll(Reader rd) throws IOException {
    StringBuilder sb = new StringBuilder();
    int cp;
    while ((cp = rd.read()) != -1) {
        sb.append((char) cp);
    }
    return sb.toString();
}

public JSONObject readJsonFromUrl(String url) throws IOException, JSONException {
    InputStream is = new URL(url).openStream();
    try {
        BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
        String jsonText = readAll(rd);
        JSONObject json = new JSONObject(jsonText);
        return json;
    } finally {
        is.close();
    }
}

public void main(String[] args) throws IOException, JSONException {
    TextView txtUser = (TextView) findViewById(R.id.user);
    JSONObject json = readJsonFromUrl("http://piggybank.wordmediavormgever.nl/getSaldo.php");
    System.out.println(json.toString());
    System.out.println(json.getString("saldo"));
    try {
        JSONObject jsonObject = new JSONObject();
        String response = jsonObject.getString("saldo");
        txtUser.setText(response);

    } catch (JSONException e) {

        e.printStackTrace();
    }
}

有人能看出我做错了什么吗？来自url的响应是 {"saldo":783}

Answer 1

我认为问题出在try块的main函数中

JSONObject jsonObject = new JSONObject();
String response = jsonObject.getString("saldo");
txtUser.setText(response);

您的jsonObject为空，您应该调用

String response = json.getString("saldo");
txtUser.setText(response);

还有一件事，当您进行一些网络呼叫时，您应该在后台线程中进行，而不是在UI线程中。（应在后台线程中调用readJsonFromUrl方法）

作为Nguyễn Trung你好ếu的回答建议

Answer 2

试试看

除去

   JSONObject jsonObject = new JSONObject();

和使用

   JSONObject json = readJsonFromUrl("http://piggybank.wordmediavormgever.nl/getSaldo.php");
  try {
    String response = json.getString("saldo");
    Log.e("AAAAAAAAA %s", response);

} 

您必须在异步任务中调用它。完成代码

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test2);
    new GetDataSync().execute();
}

String saldo = "";

public class GetDataSync extends AsyncTask<Void, Void, Void> {


    @Override
    protected Void doInBackground(Void... params) {
        try {
            getData();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        txtUser.setText(saldo);
    }
}

private void getData() throws IOException, JSONException {
    JSONObject json = readJsonFromUrl("http://piggybank.wordmediavormgever.nl/getSaldo.php");
    try {
        String response = json.getString("saldo");
        Log.e("AAAAAAAAA %s", response);
        saldo = response;

    } catch (JSONException e) {

        e.printStackTrace();
    }
}

private String readAll(Reader rd) throws IOException {
    StringBuilder sb = new StringBuilder();
    int cp;
    while ((cp = rd.read()) != -1) {
        sb.append((char) cp);
    }
    return sb.toString();
}

public JSONObject readJsonFromUrl(String url) throws IOException, JSONException {
    InputStream is = new URL(url).openStream();
    try {
        BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
        String jsonText = readAll(rd);
        JSONObject json = new JSONObject(jsonText);
        return json;
    } finally {
        is.close();
    }
}