在 Android (Java) 中全局传递 Class 变量

Question

因此，在我的应用程序的 Java 代码中，我有一个名为Pet的 class 。 这个变量是在我的应用程序中的一个活动中创建的。

到目前为止，我已经能够成功地创建这个 class 的实例，并在同一个活动中从中获取变量。

现在我想将新创建的 Class 变量 ( pet1 ) 传递给我的应用程序的 rest 并使用getPetName() function 之类的按钮在我的其他活动中显示的字符串和其他元素。

这是宠物 class

package com.example.myapplication;
import java.time.format.DateTimeFormatter;

public class Pet {

    // Variable Declarations
    private String name;
    private String species;
    private int birthday;
    private String notes = "Notes: ";
    // Replace with a clock
    // Find a way to calculate age based on time-birthday
    private int currentTime;
    //Create an array of medications

    // Creation Function
    public Pet(String petName, String petSpecies, String petBirthDay, String petNotes, String petMedication, int petDosage, String petDosageUnit){
        setPetName(petName);
        setSpecies(petSpecies);
        setBirthDay(petBirthDay);
        addNotes(petNotes);
        addMeds(petMedication, petDosage, petDosageUnit);
    }

    // Set name Function
    private void setPetName(String petName){
        name = petName;
    }

    // Get name Function
    public String getPetName(){
        return name;
    }

    // Set species Function
    private void setSpecies(String petSpecies) {
        species = petSpecies;
    }

    // Get species Function
    public String getSpecies(){
        return species;
    }

    // Set birthday Function
    private void setBirthDay(String petBirthDay) {
        // Convert Birthday to integer
        //birthday = petBirthDay;
    }

    // Get age Function
    public int getAge(){
        // We calculate the age by taking the BirthDay and subtracting the current time
        return (currentTime - birthday);
    }

    // Add notes Function
    public void addNotes(String newNotes){
        // There are no current notes
        if (notes == "Notes: ") {
            notes = notes + newNotes;
        }
        // Make a new line and append the new notes
        else {
            notes = notes + "\n" + newNotes;
        }
    }

    // Get notes Function
    public String getNotes(){
        return notes;
    }

    // Combine Medication Information and add to Array
    public void addMeds(String medName, int medDosage, String unit){
        String medInfo = medName + " : " + medDosage + unit;
    }
    

}

这是创建 class 实例的活动

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;

public class AddPetScreen extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
    private Button addPetButton;

    private EditText petNameText;
    private EditText petBirthdayText;
    private EditText petNotesText;

    private Spinner petSpeciesSpinner;
    private String speciesChoice;

    private String petNameTextVal;
    private String petBDayTextVal;
    private String petNotesTextVal;

    public Pet pet1;
    //public static final Pet GLOBAL_PET = "com.example.myapplication.GLOBAL_PET";

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

        petNameText = (EditText)findViewById(R.id.addPetNameField);
        petBirthdayText = (EditText)findViewById(R.id.addPetBirthdayField);
        petNotesText = (EditText) findViewById(R.id.addPetNotesField);

        petSpeciesSpinner = findViewById(R.id.addPetSpeciesSpinner);

        ArrayAdapter<CharSequence> speciesAdapter = ArrayAdapter.createFromResource(this, R.array.Species, android.R.layout.simple_spinner_dropdown_item);
        speciesAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        petSpeciesSpinner.setAdapter(speciesAdapter);
        petSpeciesSpinner.setOnItemSelectedListener(this);


        // Button to create Pet in Pet Class and Add
        addPetButton = (Button) findViewById(R.id.addPetAddPetButton);
        addPetButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addPet();
            }
        });
    }

    // Function to create Pet in Pet class and Add
    public void addPet() {
        // Need to parse variables from text boxes and spinner
        petNameTextVal = petNameText.getText().toString();
        petNotesTextVal = petNotesText.getText().toString();
        petBDayTextVal = petBirthdayText.getText().toString();
        // NOTE: Do not pass in medication, since that is the Veterinarians Job

        // Check for empty parameters
        if (petNameText.getText().toString().isEmpty()) {
            Toast.makeText(getApplicationContext(), "Please Enter a Pet Name", Toast.LENGTH_SHORT).show();
        }
        else if (petBirthdayText.getText().toString().isEmpty()){
                Toast.makeText(getApplicationContext(),"Please Enter a Birth Date (YYYY/MM/DD)",Toast.LENGTH_SHORT).show();
        }
        // All necessary values are given
        else {
            if (checkBirthdayValidity() == false){
                Toast.makeText(getApplicationContext(), "Date Incorrect", Toast.LENGTH_SHORT).show();
            }
            else {
                // If there are no notes, set it to the empty string
                if (petNotesText.getText().toString().isEmpty()) {
                    petNotesTextVal = "";
                }
                // Create Pet
                pet1 = new Pet(petNameTextVal, speciesChoice, petBDayTextVal, petNotesTextVal, "", 0, "");
                Toast.makeText(getApplicationContext(), "Success! " + pet1.getPetName() + " was added", Toast.LENGTH_SHORT).show();

            }
        }
    }

    // Check if the birthday is in YYYY/MM/DD format
    public boolean checkBirthdayValidity(){
        petBDayTextVal = petBirthdayText.getText().toString();
        String year;
        year = petBDayTextVal.substring(0, 4);

        // Check that the birthday is a valid input
        if(petBDayTextVal.length() != 10){
            Toast.makeText(getApplicationContext(),"Incorrect Date, Please check your input",Toast.LENGTH_SHORT).show();
            return false;
        }
        else if (petBDayTextVal.substring(0, 4).matches("-?\\d+") == false) {
            Toast.makeText(getApplicationContext(), "Incorrect Year input", Toast.LENGTH_SHORT).show();
            return false;
        }
        else if (Integer.valueOf(petBDayTextVal.substring(0, 4)) <= 1989 || Integer.valueOf(petBDayTextVal.substring(0, 4)) >= 2022){
            Toast.makeText(getApplicationContext(), "Incorrect Year input: Please input a Year between 1990 and 2021", Toast.LENGTH_SHORT).show();
            return false;
        }
        // Year has been checked, now check Month
        else if (petBDayTextVal.substring(4, 5).contains("/") == false){
            Toast.makeText(getApplicationContext(),"Forgot the / after Year",Toast.LENGTH_SHORT).show();
            return false;
        }
        else if (petBDayTextVal.substring(5, 7).matches("-?\\d+") == false){
            Toast.makeText(getApplicationContext(), "Incorrect Month input", Toast.LENGTH_SHORT).show();
            return false;
        }
        else if (Integer.valueOf(petBDayTextVal.substring(5, 7)) <= 0 || Integer.valueOf(petBDayTextVal.substring(5, 7)) >= 13){
            Toast.makeText(getApplicationContext(), "Incorrect Month input: Please input a Month between 01 and 12", Toast.LENGTH_SHORT).show();
            return false;
        }
        // Month has been checked, now check Day
        else if (petBDayTextVal.substring(7, 8).contains("/") == false){
            Toast.makeText(getApplicationContext(), "Forgot the / after Month", Toast.LENGTH_SHORT).show();
            return false;
        }
        else if (petBDayTextVal.substring(8, 10).matches("-?\\d+") == false){
            Toast.makeText(getApplicationContext(), "Incorrect Day input", Toast.LENGTH_SHORT).show();
            return false;
        }
        // Check for 31 Day Months
        else if (Integer.valueOf(petBDayTextVal.substring(5, 7)) == 1 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 3 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 5 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 7 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 8 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 10 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 12){
            if (Integer.valueOf(petBDayTextVal.substring(8, 10)) <= 0 || Integer.valueOf(petBDayTextVal.substring(8, 10)) >= 32) {
                Toast.makeText(getApplicationContext(), "Incorrect Date for Month input: Please input a Date between 01 and 31", Toast.LENGTH_SHORT).show();
                return false;
            }
        }
        // Check for 30 Day Months
        else if (Integer.valueOf(petBDayTextVal.substring(5, 7)) == 4 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 6 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 9 || Integer.valueOf(petBDayTextVal.substring(5, 7)) == 11){
            if (Integer.valueOf(petBDayTextVal.substring(8, 10)) <= 0 || Integer.valueOf(petBDayTextVal.substring(8, 10)) >= 31) {
                Toast.makeText(getApplicationContext(), "Incorrect Date for Month input: Please input a Date between 01 and 30", Toast.LENGTH_SHORT).show();
                return false;
            }
        }
        // Check for February
        else if (Integer.valueOf(petBDayTextVal.substring(5, 7)) == 2 && (Integer.valueOf(petBDayTextVal.substring(8, 10)) >= 0 || Integer.valueOf(petBDayTextVal.substring(8, 10)) >= 29)){
            Toast.makeText(getApplicationContext(), "Incorrect Date for Month input: Please input a Date between 01 and 28\n NOTE: Input 28 if Pet was born on a leap year 29th", Toast.LENGTH_SHORT).show();
            return false;
        }
        // All checks have been passed: Birthday is correct format
        return true;
    }

    // Set Species based on what is selected
    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        speciesChoice = parent.getItemAtPosition(position).toString();
    }

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

    }
}

这是我希望宠物名称显示为按钮文本的屏幕。 请注意，我当前将其设置为表示占位符的字符串。 由于此屏幕也出现在 Class 变量创建之前。

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.content.Intent;
import android.net.Uri;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class SelectPetScreen extends AppCompatActivity {
    // Button Declarations
    private Button addPetButton;
    private Button selectPetButton;
    private Button pet1Button;
    private String selectPetButtonText;


    //Pet pet1 = getResources().getPet();

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

        addPetButton = (Button)findViewById(R.id.selectPetPet1Button);

        // Set the Pet's name from the class here
        // When there is an instance of the Pet class use getPetName() to set the name to the Button text
        addPetButton.setText("Placeholder name");

        // Button to navigate to Add a Pet
        addPetButton = (Button) findViewById(R.id.selectPetAddPetButton);
        addPetButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openAddPetScreen();
            }
        });
    }

    // Function to open Add Pet Screen
    public void openAddPetScreen() {
        Intent intent = new Intent(this, AddPetScreen.class);
        startActivity(intent);
    }
}

我搜索了很多，我能找到的只是与字符串和整数等简单变量有关的东西

Answer 1

让Pet成为您的应用程序class 的成员，这样您就可以在任何地方访问它，而无需在活动之间传递它。

Answer 2

您想要的似乎是Singleton ：一个 class 只有一个实例，可以在整个应用程序中全局使用。

但更合适的解决方案是将所需的数据传递给活动。 这可以通过使用Intent本身来实现：

public void openAddPetScreen() {
    Intent intent = new Intent(this, AddPetScreen.class);
    intent.putExtra(SelectPetScreen.EXTRA_PET_NAME, petName);
    startActivity(intent);
}

然后在SelectPetScreen活动中获取数据：

public static final String EXTRA_PET_NAME = "extra_name";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Intent intent = getIntent();
    if(intent != null) {
        String petName = intent.getExtra(EXTRA_PET_NAME);
        if (petName != null) {
            // do logic with the petName
        }
    }
}

如果您需要传递整个Pet object，那么您可以使其扩展Parcelable 并使用intent.putParcelableExtra传递它