Arraylist 不工作，项目不堆叠

Question

所以，我试图从database 获取一些信息并将其保存到ArrayList，以便稍后我可以根据该列表中的length 和items 动态添加buttons。

代码：

private List<String> probleme = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home);

    if (SharedPrefManager.getInstance(this).isLoggedIn()) {
        CautaProbleme();
        for(int i=0; i<probleme.size(); i++) {
            Button myButton = new Button(this);
            myButton.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT));
            myButton.setText(probleme.get(i));
            LinearLayout layout = (LinearLayout) findViewById(R.id.linear_home);
            layout.addView(myButton);
        }
    }`

CautaProbleme 方法：

private void CautaProbleme(){
    class CautaProbleme extends AsyncTask<Void, Void, String> {
        User user = SharedPrefManager.getInstance(getApplicationContext()).getUser();
        final String departament = String.valueOf(user.getDepartament());
        @Override
        protected String doInBackground(Void... voids) {
            //creating request handler object
            RequestHandler requestHandler = new RequestHandler();

            //creating request parameters
            HashMap<String, String> params = new HashMap<>();
            params.put("departament", departament);

            //returing the response
            return requestHandler.sendPostRequest(URLs.URL_PROBLEME, params);
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            //displaying the progress bar while user registers on the server
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            //hiding the progressbar after completion

            try {
                //converting response to json object
                JSONObject obj = new JSONObject(s);

                //if no error in response
                if (!obj.getBoolean("error")) {
                    JSONArray problemeArray = obj.getJSONArray("probleme");
                    for (int i = 0; i < problemeArray.length(); i++) {
                        JSONObject problema = problemeArray.getJSONObject(i);
                        // Verificare daca s-au primit probleme trimise de server
                        if (!problema.isNull("Problema")) {
                            String situatie = problema.getString("Problema");
                            probleme.add(situatie);
                        }
                    }

                } else {
                    Toast.makeText(getApplicationContext(), "Some error occurred", Toast.LENGTH_SHORT).show();
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }
    CautaProbleme ru =new CautaProbleme();
    ru.execute();
}

JSON 响应没关系，problemeArray 看起来不错，但问题是.add() 命令没有将strings 添加到列表中，所以用于创建buttons 的for 确实什么都不做，有一个空的list。我已经在全球范围内声明了private List probleme = new ArrayList<>();。

Answer 1

AsyncTask 是异步执行的，所以你必须等到执行完成才能获取数据。更好的选择是在操作完成时使用回调来调用。

步骤 - 1： 从onCreate 中移除按钮创建代码并将其添加到回调中

@Override
protected void onCreate(Bundle savedInstanceState) {

    ....

    if (SharedPrefManager.getInstance(this).isLoggedIn()) {
        CautaProbleme();
    }
}

在此处添加回调函数和更新逻辑

private void createButtonDynamically() {
    LinearLayout layout = (LinearLayout) findViewById(R.id.linear_home);

    for (int i = 0; i < probleme.size(); i++) {
        Button myButton = new Button(this);
        myButton.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT));
        myButton.setText(probleme.get(i));
        layout.addView(myButton);
    }
}

步骤 - 2： 操作完成时从onPostExecute 调用回调

class CautaProbleme extends AsyncTask<Void, Void, String> {

    ....

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);

        ....

        createButtonDynamically();
    }
}

Answer 2

CautaProbleme 在您进行for 循环时在后台运行。 您应该将带有onReady() 方法的接口发送到ASyncTask 并从onPostExecute 调用它。

然后，在你实现（Activity）onReady()的地方，你可以做

 for(int i=0; i<probleme.size(); i++) {
        Button myButton = new Button(this);
        myButton.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT));
        myButton.setText(probleme.get(i));
        LinearLayout layout = (LinearLayout) findViewById(R.id.linear_home);
        layout.addView(myButton);
    }