这种情况下是否存在可以有效解决以下问题的机制？即，在MainActivity中按下按钮后，我转到SecondActivity，输入数据，然后在SecondActivity中按下按钮并返回MainActivity。
我检索数据，将其分配给变量，然后创建一个放置在数组中的对象。
我声明并初始化了静态变量index = 0，它也负责 日期更改和数组索引。
我创建了两个方法String imageButtonUp（）和String imageButtonDown（）。 当您按下更改日期的按钮时，将调用这些方法。 如果按下ButtonUp按钮，则变量索引将增加1，然后 将显示下一个日期，而如果按下ButtonDown按钮，则静态变量将减少1，则将显示上一个日期。
问题是，启动应用程序后，一切正常，直到... 当我按下ButtonUp按钮时，索引变量将增加1，因此第二天将出现，并且数组索引将增加为正值。
当我按下ButtonDown时会出现问题，因为变量索引变为负数，这使得 为表的索引分配负值，并且应用程序自动关闭。
一种解决方案是创建一个静态变量，该变量将负责数组的索引。 我可以初始化此变量index = 1000，并创建一个包含2,000个元素的数组。 因此，按下ButtonDown不会收到错误消息，因为索引将为999、998、997 ...
还有其他更有效的解决方案吗？
这是我的代码：
MainActivity：
public class MainActivity extends AppCompatActivity {
TextView textView, textView2, textView3;
ImageButton imageButtonDown, imageButtonUp;
Button button;
private static final int REQUEST_CODE = 1;
Date_Information Up_and_Down = new Date_Information("Day", 0);
Date_Information array[] = new Date_Information[500];
String day;
int deegres;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = findViewById(R.id.textView);
textView2 = findViewById(R.id.textView2);
textView3 = findViewById(R.id.textView3);
imageButtonDown = findViewById(R.id.imageButton1);
imageButtonUp = findViewById(R.id.imageButton2);
button = findViewById(R.id.button2);
array[0] = Up_and_Down;
Up_and_Down.setDate();
textView.setText(Up_and_Down.setDate());
imageButtonDown.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
textView.setText(Up_and_Down.imageButtonDown());
if(array[Date_Information.index] == null) {
textView2.setText("Day:");
textView3.setText("Deegres Celsius:");
}
else {
textView2.setText(array[Date_Information.index].getDay());
textView3.setText(array[Date_Information.index].getDegrees_Celsius());
}
}
});
imageButtonUp.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
textView.setText(Up_and_Down.imageButtonUp());
if(array[Date_Information.index] == null) {
textView2.setText("Day:");
textView3.setText("Deegres Celsius:");
}
else {
textView2.setText(array[Date_Information.index].getDay());
textView3.setText(array[Date_Information.index].getDegrees_Celsius());
}
}
});
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent i = new Intent(MainActivity.this, SecondActivity.class);
startActivityForResult(i, REQUEST_CODE);
}
});
}
protected void onActivityResult(int requestCode, int resultCode, Intent i) {
if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
day = i.getStringExtra("day");
deegres = i.getIntExtra("deegres", 0);
Date_Information test = new Date_Information(day, deegres);
array[Date_Information.index] = test;
textView2.setText(array[Date_Information.index].getDay());
textView3.setText(array[Date_Information.index].getDegrees_Celsius());
}
}
}
SecondActivity：
public class SecondActivity extends AppCompatActivity {
EditText editText1, editText2;
Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
editText1 = findViewById(R.id.editText);
editText2 = findViewById(R.id.editText2);
button = findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
sendInformation();
}
});
}
public void sendInformation() {
String day = editText1.getText().toString();
int deegres = Integer.parseInt(editText2.getText().toString());
Intent i = new Intent();
i.putExtra("day", day);
i.putExtra("deegres", deegres);
setResult(RESULT_OK, i);
finish();
}
}
和Date_Information类：
public class Date_Information {
Calendar calendar; //The reference variable that will store the Calendar instance
SimpleDateFormat dateFormat ; //Reference variable that will refer to the object that is responsible for the date format
String formattedDate; //Formatted date
private String day; //Day
private int degrees_Celsius; //Deegres C
static int index = 0;
//The parametrised constructor, which sets the date format, assigns the sent day and the component step of the object
Date_Information(String day, int degrees_Celsius) {
dateFormat = new SimpleDateFormat("dd - MMM - yyyy");
this.day = day;
this.degrees_Celsius = degrees_Celsius;
}
Date_Information() {
dateFormat = new SimpleDateFormat("dd - MMM - yyyy");
}
//The method returns the formatted date
String setDate() {
calendar = Calendar.getInstance(); //Get the instance and assigning it to the reference variable calendar
formattedDate = dateFormat.format(calendar.getTime()); //Formatting the downloaded date and assigning to the variable formattedDate
return formattedDate;
}
//A method that increases the date by 1 day
String imageButtonUp() {
index++;
calendar = Calendar.getInstance();
calendar.add(Calendar.DATE, index);
formattedDate = dateFormat.format(calendar.getTime());
return formattedDate;
}
//
//Method that reduces the date by 1 day
String imageButtonDown() {
index --;
calendar = Calendar.getInstance();
calendar.add(Calendar.DATE, index);
formattedDate = dateFormat.format(calendar.getTime());
return formattedDate;
}
String getDay() {
return day;
}
String getDegrees_Celsius() {
return String.valueOf(degrees_Celsius);
}
}