java - Android - 后退按钮导致问题

Question

我正在尝试创建一个应用程序来跟踪用户访问过的国家/地区。从下拉旋转器中选择一个国家/地区，然后在文本字段中输入一个数字。下一个屏幕应按频率顺序显示访问最多的三个国家/地区。

第一次输入国家/地区和频率时，它工作正常，但当您按后退按钮，然后选择不同的国家/地区并输入另一个频率时，就会出现问题，它不会将频率分配给正确的国家/地区。

举个例子，如果您首先选择奥地利，访问次数为 5，然后按下一步，它会显示:

Austria       5
Wales         0
Switzerland   0

如果按返回键，然后选择比利时并输入 10，则会显示

Denmark       10
Austria       5
Wales         0

如果您第三次返回并选择卢森堡并输入 15，则会显示

Spain         15
Denmark       10
Austria       5

似乎countryList数组与微调器位置变得不同步，我不知道如何修复它，任何帮助将不胜感激。

这是我尝试制作的第一个 Android 应用程序，因此可能还有其他我不知道的错误。

谢谢

这是第一个 Activity :

package com.example.country;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Spinner;

import java.util.Collections;

public class Select extends AppCompatActivity {

ImageView flagChoiceView;
Spinner spinnerCountry;
ArrayAdapter<CharSequence> adapter;
public static Button next2;
int elementPosition;

//Declaring all objects of type country
country Austria = new country("Austria");
country Belgium = new country("Belgium");
country Denmark = new country("Denmark");
country England = new country("England");
country France = new country("France");
country Germany = new country("Germany");
country Ireland = new country("Ireland");
country Italy = new country("Italy");
country Luxembourg = new country("Luxembourg");
country Portugal = new country("Portugal");
country Spain = new country("Spain");
country Sweden = new country("Sweden");
country Switzerland = new country("Switzerland");
country Wales = new country("Wales");

//Creating an array of type country in preparation for sorting
country[] countryList = {Austria, Belgium, Denmark,England,France,
        Germany,Ireland,Italy,Luxembourg,Portugal,Spain,Sweden,Switzerland,Wales};

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_select);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    afterSecondClick();



    //Setting protocols for entering values into the text field
    final TextWatcher numberInput = new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) { }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            try{
                countryList[elementPosition].setFrequency(Integer.parseInt(s.toString()));
            }
            catch(NumberFormatException e)
            {
                countryList[elementPosition].setFrequency(0);
            }
        }

        @Override
        public void afterTextChanged(Editable s) { }
    };

    //Creating a listener for the input field
    EditText inputFrequency = (EditText)findViewById(R.id.inputFrequency);
    inputFrequency.addTextChangedListener(numberInput);

    //sortFunction(countryList);
    spinnerCountry = (Spinner)findViewById(R.id.dropdown);
    adapter = ArrayAdapter.createFromResource(this,R.array.country_list,android.R.layout.simple_spinner_item);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinnerCountry.setAdapter(adapter);
    spinnerCountry.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, final int position, long id) {

            flagChoiceView = (ImageView) findViewById(R.id.flagChoice);

            elementPosition = position;
           switch(position)
           {
               case 0:

                   flagChoiceView.setImageResource(R.drawable.austriaflag);
               break;

               case 1:
                   flagChoiceView.setImageResource(R.drawable.belgiumflag);
                   break;

               case 2:
                   flagChoiceView.setImageResource(R.drawable.denmarkflag);
                   break;

               case 3:
                   flagChoiceView.setImageResource(R.drawable.englandflag);
                   break;

               case 4:
                   flagChoiceView.setImageResource(R.drawable.franceflag);
                   break;

               case 5:
                   flagChoiceView.setImageResource(R.drawable.germanflag);
                   break;

               case 6:
                   flagChoiceView.setImageResource(R.drawable.irelandflag);
                   elementPosition = position;
                   break;

               case 7:
                   flagChoiceView.setImageResource(R.drawable.italyflag);
                   break;

               case 8:
                   flagChoiceView.setImageResource(R.drawable.luxembourgeflag);
                   break;

               case 9:
                   flagChoiceView.setImageResource(R.drawable.portugalflag);
                   break;

               case 10:
                   flagChoiceView.setImageResource(R.drawable.spainflag);
                   break;

               case 11:
                   flagChoiceView.setImageResource(R.drawable.swedenflag);
                   break;

               case 12:
                   flagChoiceView.setImageResource(R.drawable.switzerlandflag);
                   break;

               case 13:
                   flagChoiceView.setImageResource(R.drawable.walesflag);
                   break;

               default:
                   flagChoiceView.setImageResource(R.drawable.austriaflag);
                   break;

           }

        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {

        }
    });

}

//Linking the second activity to the third with a button click
public void afterSecondClick()
{
    next2 = (Button)findViewById(R.id.button);
    next2.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v){
                    sortFunction(countryList);



                    Intent proceedAgain = new Intent("com.example.country.Results");
                    proceedAgain.putExtra("firstCountry", countryList[13].getName());
                    proceedAgain.putExtra("secondCountry", countryList[12].getName());
                    proceedAgain.putExtra("thirdCountry", countryList[11].getName());
                    proceedAgain.putExtra("firstFrequency", countryList[13].getFrequency());
                    proceedAgain.putExtra("secondFrequency", countryList[12].getFrequency());
                    proceedAgain.putExtra("thirdFrequency", countryList[11].getFrequency());
                    startActivity(proceedAgain);
                    EditText inputFrequency=(EditText) findViewById(R.id.inputFrequency);
                    inputFrequency.setText("");



                }
            }
    );
}

//Declaring a new inner class known as country
private class country
{
    private String name;
    private int frequency;

    public country(String Name){
        this.name = Name;
        this.frequency = 0;
    }

    public country(){
        this.name = "";
        this.frequency = 0;
    }

    public void setFrequency(int freq){
        this.frequency = freq;
    }

    public int getFrequency(){
        return frequency;
    }

    public String getName(){
        return name;
    }
}

//Sorting algorithm from lowest frequency to highest
void sortFunction(country[] List){
    int count = 0;
    while(count < List.length){
        for(int n = 0; n < List.length - 1; n++){
            if(List[n].getFrequency() > List[n+1].getFrequency())
                swapFunction(List, n);
        }
        count++;
    }
}

//Counterpart Method to sortFunction
void swapFunction(country[] List, int m){
    country a, b, c;
    a = List[m];
    b = List[m+1];
    c = a;
    List[m+1] = c;
    List[m] = b;
}
}

这是第二个 Activity :

package com.example.country;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.TextView;

public class Results extends AppCompatActivity

{
//Inflation of GUI and toolbar for the activity
@Override
protected void onCreate(Bundle savedInstanceState)

{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_results);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    Bundle extras = getIntent().getExtras();

    TextView countryOne = (TextView)findViewById(R.id.firstCountry);
    countryOne.setText(extras.getString("firstCountry"));

    TextView countryTwo = (TextView)findViewById(R.id.secondCountry);
    countryTwo.setText(extras.getString("secondCountry"));

    TextView countryThree = (TextView)findViewById(R.id.thirdCountry);
    countryThree.setText(extras.getString("thirdCountry"));

    TextView freqOne = (TextView)findViewById(R.id.firstFrequency);
    freqOne.setText(String.valueOf(extras.getInt("firstFrequency")));

    TextView freqTwo = (TextView)findViewById(R.id.secondFrequency);
    freqTwo.setText(String.valueOf(extras.getInt("secondFrequency")));

    TextView freqThree = (TextView)findViewById(R.id.thirdFrequency);
    freqThree.setText(String.valueOf(extras.getInt("thirdFrequency")));
}

}

数组的 xml 在这里:

<resources>
<string name="app_name">COUNTry</string>
<string name="action_settings">Settings</string>
<string name="appName">Welcome!</string>
<string name="nextButtonValue">NEXT</string>
<string name="title_activity_select">Select</string>
<string-array name="country_list">
    <item>Austria</item>
    <item>Belgium</item>
    <item>Denmark</item>
    <item>England</item>
    <item>France</item>
    <item>Germany</item>
    <item>Ireland</item>
    <item>Italy</item>
    <item>Luxembourg</item>
    <item>Portugal</item>
    <item>Spain</item>
    <item>Sweden</item>
    <item>Switzerland</item>

Answer 1

在上面的示例中:

问题在于，当您选择比利时时，elementPosition 为 1，但您已对国家/地区列表进行了排序，因此列表中的比利时位于位置 0 而不是 1>。因此它更新了位于位置 1 的丹麦的频率(国家列表中的第二个)。

要解决此问题，如果国家/地区的频率与给定国家/地区名称(例如比利时)匹配，而不是旋转器上的国家/地区位置(因为旋转器未排序且不匹配)，则应修改该国家/地区的频率。

因此，一种方法是搜索列表中的每个国家/地区，如果其名称与旋转器所选项目的名称匹配(国家/地区名称，请使用 .equals() 检查)，然后更新其频率。

<小时/>

此外，您的代码还有另一个问题，如果您首先输入文本值，然后然后选择国家/地区，则更新将发送到错误的国家/地区 。因此，您必须在按钮的 onClick 方法中对 EditText 执行任何操作(更新频率)。

<小时/>

因此，解决方案代码将类似于:

在 afterSecondClick 方法内 -> 在 onClick 方法内 -> 在你的 R.id.button 按钮中:

排序之前!!!(此行之前: sortFunction(countryList); )

EditText ed = (EditText) findViewById(R.id.inputFrequency);


Spinner spinner = (Spinner)findViewById(R.id.dropdown);
String text = spinner.getSelectedItem().toString();


int count = 0;
while(count < countryList.length)
{
    if((countryList[count]).getName().equals(text))
    {
        try
        {
            countryList[count].setFrequency(Integer.parseInt(ed.toString()));
        }
        catch(NumberFormatException e)
        {
            countryList[count].setFrequency(0);
        }
    }
    count++;
}

时间复杂度为 O(n)。您的排序算法的时间复杂度为 O(n^2)，因此它不会对速度产生太大影响。此外，对于少数国家(大约 100 个)来说，它可以被认为是快速的。还可以尝试使用快速排序作为排序算法以提高速度(但对于少数国家/地区来说仍然可以，因为您现在就有它)

并且还从 EditText 中删除 TextWatcher。