无法在 android 微调器中添加提示

Question

我有一个 spinner，它在我的 android application 中表现得像 dropdown。我正在 android studio 开发应用程序。微调器从 api 获取数据。在运行时，它从 API 得到 usernames 并显示在 spinner 中。当应用运行s 时，它显示 selected 用户的 username 和 ID，如下图

所示

现在我想添加提示，所以我搜索了很多文章并找到了很多解决方案，我遵循了其中最简单的一个。更多理解请看下面的代码

 try
        {
            JSONObject jobj = new JSONObject(jsonObject.toString());
            // Locate the NodeList name
            jsonArray = jobj.getJSONArray("users");

            for(int i=0; i<jsonArray.length(); i++)
            {
                jsonObject = jsonArray.getJSONObject(i);

                Users user = new Users();

                user.setId(jsonObject.optString("Id"));
                user.setName(jsonObject.optString("Name"));
                users.add(user);

                userList.add("Select a username");// i add this as a hint
                userList.add(jsonObject.optString("Name"));

            }
        } catch (JSONException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }

现在使用 onPostExecute() 方法

  @Override
    protected void onPostExecute(Void args)
    {
        // Locate the spinner in activity_main.xml
        Spinner spinner = (Spinner)findViewById(R.id.spinner);

        // Spinner adapter
        spinner.setAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_spinner_dropdown_item, userList));

        // Spinner on item click listener

        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {


            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

                textViewResult = (TextView)findViewById(R.id.textView);

                // Set the text followed by the position

                // Set the text followed by the position
                if(!users.get(position).getName().equals("Select a username")) {
                    textViewResult.setText(" " + users.get(position - 1).getName() + "  " + users.get(position - 1).getId());
                }else {

                    textViewResult.setText("Hi " + users.get(position).getName() + " your ID is " + users.get(position).getId());
                    UserId = String.valueOf(users.get(position).getId());
                    progressDialog.dismiss();
                    _latitude.setText("");
                    _longitude.setText("");
                    Latitude = null;
                    Longitude = null;

                }

            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
                textViewResult.setText("");
            }
        });
    }

当我运行应用程序崩溃时，出现以下错误

Process: com.example.accurat.myapp, PID: 30382
                                                                       java.lang.ArrayIndexOutOfBoundsException: length=12; index=-1
                                                                           at java.util.ArrayList.get(ArrayList.java:310)
                                                                           at com.example.accurat.myapp.MainActivity$DownloadJSON.onItemSelected(MainActivity.java:494)
                                                                           at android.widget.AdapterView.fireOnSelected(AdapterView.java:931)
                                                                           at android.widget.AdapterView.dispatchOnItemSelected(AdapterView.java:920)
                                                                           at android.widget.AdapterView.-wrap1(AdapterView.java)
                                                                           at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:890)
                                                                           at android.os.Handler.handleCallback(Handler.java:746)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5491)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)

此错误发生在 textViewResult.setText(" " + users.get(position - 1).getName() + " " + users.get(position - 1).getId());

点

更新 1

根据 Junaid Hafeez 的回答，我做了以下

for(int i=0; i<jsonArray.length(); i++)
            {
                jsonObject = jsonArray.getJSONObject(i);

                Users user = new Users();

                user.setId(jsonObject.optString("Id"));
                user.setName(jsonObject.optString("Name"));
                users.add(user);


                userList.add(jsonObject.optString("Name"));

            }
            userList.add(0, "Select a username"); // after for loop ended i add `select a username` at `0` index

之后在 postExecute() 方法中我做了以下

 @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

                textViewResult = (TextView)findViewById(R.id.textView);

                // Set the text followed by the position

                // Set the text followed by the position
                if(position>0)
                {
                    textViewResult.setText("Hi " + users.get(position).getName() + " your ID is " + users.get(position).getId());

                    UserId = String.valueOf(users.get(position).getId());

                    _latitude.setText("");
                    _longitude.setText("");
                    Latitude = null;
                    Longitude = null;
                }
                else {


                }

                progressDialog.dismiss();

            }

我得到的结果低于

它确实向我显示了提示，但是当我 select 任何用户名时，它会向我显示下一个用户名的 name 和 id，如下图

我一直坚持，找不到任何解决方案

非常感谢任何帮助。

Answer 1

可能您正在做的是，您正在单击微调器的第一项，其中 position = 0 并在 setText 中执行 position - 1 这使得索引 -1 实际上不存在并且崩溃了。其次你这样做

 userList.add("Select a username");// i add this as a hint

在你的循环中，它在每次迭代中添加新项目。你需要做的是

获得完整的数据列表后，像这样在它的 0 索引上添加提示

userList.add(0, "Select a username");

在你的 onClick 中，检查天气 position > 0 然后做你的工作，否则当用户点击提示时忽略。

Answer 2

你好使用下面的库作为提示微调器

Hint Spinner library

Answer 3

package com.keshav.spinnerhintexample;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

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

        final Spinner spinner = (Spinner) findViewById(R.id.spinner);
        btn_submit = (Button) findViewById(R.id.btn_submit);



        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item) {

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {

                View v = super.getView(position, convertView, parent);
                if (position == getCount()) {
                    ((TextView)v.findViewById(android.R.id.text1)).setText("");
                    ((TextView)v.findViewById(android.R.id.text1)).setHint(getItem(getCount())); //"Hint to be displayed"
                }

                return v;
            }

            @Override
            public int getCount() {
                return super.getCount()-1; // you dont display last item. It is used as hint.
            }

        };


        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        adapter.add("Daily");
        adapter.add("Two Days");
        adapter.add("Weekly");
        adapter.add("Monthly");
        adapter.add("Three Months");
        adapter.add("Select a Item"); //This is the text that will be displayed as hint.


        spinner.setAdapter(adapter);
        spinner.setSelection(adapter.getCount()); //set the hint the default selection so it appears on launch.
        // spinner.setOnItemSelectedListener(this);


        btn_submit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String item=spinner.getSelectedItem().toString();

                Log.e("keshav","selectedItem is ->"  + item);

                if(spinner.getSelectedItem().toString().equals("Select a Item")){
                    Toast.makeText(MainActivity.this,"Please Select an Item",Toast.LENGTH_LONG).show();
                }else {
                    Toast.makeText(MainActivity.this,"selected Item is -> "+item,Toast.LENGTH_LONG).show();
                }
            }
        });
    }
}

-------------------Xml File ----------


<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.keshav.spinnerhintexample.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />


    <Spinner
        android:id="@+id/spinner"
        android:layout_width="match_parent"
        android:layout_height="45dp"
        android:layout_marginTop="40dp"
        />


    <Button
        android:id="@+id/btn_submit"
        android:layout_width="match_parent"
        android:layout_height="45dp"
        android:layout_alignParentBottom="true"
        android:layout_margin="10dp"
        android:background="@color/colorPrimaryDark"
        android:text="Submit"
        android:textColor="#FFFFFF"

        />

</RelativeLayout>

无法在 android 微调器中添加提示

Unable to add hint in android spinner

android

android-spinner

android-studio