android - Parcelable 对象在接收 Activity 时为 Null

Question

我已经将 Parcelable 实现到一个对象中，我想在成功登录的 Activity 之间传递。唯一的问题是对象(用户)在收到 Intent 时总是有空字段。

我已经在这里搜索了很多问题，但我现在完全被困住了，因为我似乎找不到问题。

我作为 extra 传递给 Intent 的对象具有正确的值，但无论我如何尝试接收它，它始终具有空字段。

这是我的用户类:

public class User implements Parcelable{

private String name;
private String email;
private String password;
private int age;
private int weight;
private int height;
private long id;


public User(String name, String email, String password, int age, int weight, int height, long id) {

this.name = name;
this.email = email;
this.password = password;
this.age = age;
this.weight = weight;
this.height = height;
this.id = id;
}

public User(String name, String email, String password) {
    this.name = name;
    this.email = email;
    this.password = password;
}

/**
 * empty constructor
 */
public User(){
}

@Override
public String toString() {
    return "User{" +
            "name='" + name + '\'' +
            ", email='" + email + '\'' +
            ", password='" + password + '\'' +
            ", age=" + age +
            ", weight=" + weight +
            ", height=" + height +
            ", id=" + id +
            '}';
}

public long getId() {
    return id;
}

public void setId(long id) {
    this.id = id;
}

public void setName(String name) {
    this.name = name;
}

public String getName() {

    return name;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

public String getPassword() {
    return password;
}

public void setPassword(String password) {
    this.password = password;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

public int getWeight() {
    return weight;
}

public void setWeight(int weight) {
    this.weight = weight;
}

public int getHeight() {
    return height;
}

public void setHeight(int height) {
    this.height = height;
}

//Parcelable methods below.


// 99.9% of the time you can just ignore this
public int describeContents() {
    return 0;
}

// write your object's data to the passed-in Parcel
public void writeToParcel(Parcel out, int flags) {
    out.writeString(name);
    out.writeString(email);
    out.writeInt(age);
    out.writeInt(weight);
    out.writeInt(height);
    out.writeLong(id);
}

// this is used to regenerate your object. All Parcelables must have a CREATOR that implements these two methods
public static final Parcelable.Creator< User> CREATOR = new Parcelable.Creator<User>() {
    public User createFromParcel(Parcel in) {
        return new User(in);
    }
    public User[] newArray(int size) {
        return new User[size];
    }
};

// example constructor that takes a Parcel and gives you an object populated with it's values
private User(Parcel in) {
    User pUser = new User();
    pUser.setName(in.readString());
    pUser.setEmail(in.readString());
    pUser.setAge(in.readInt());
    pUser.setWeight(in.readInt());
    pUser.setHeight(in.readInt());
    pUser.setId(in.readLong());
    }
}

这是我的主要 Activity ，它创建发送 Parcelable extra 的 Intent :

public class MainActivity extends AppCompatActivity {

private DatabaseHelper db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
   // ifActEmpty(db);


}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu items for use in the action bar
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu_main, menu);
    return super.onCreateOptionsMenu(menu);
}

public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

/**
 * Method called when the register link button is clicked. Calls intent to start the
 * registerActivity.
 * @param v
 */
public void navigateToRegister(View v){
    Intent intent = new Intent(getApplicationContext(), RegisterActivity.class);
    intent.addFlags(intent.FLAG_ACTIVITY_CLEAR_TOP);
    startActivity(intent);
    finish();
}

/**
 * method called when the login button is clicked. Takes the input from username and password
 * edittext fields and queries the database to see if valid user. Returns an intent to go to
 * homeActivity.
 * @param view
 */
public void login(View view){
    db = new DatabaseHelper(this);
    //when this button is clicked we need to access the DB to see if the users
    // credentials typed into the two edittext fields match those in the DB.

    final EditText emailEditText = (EditText) findViewById(R.id.loginEmail);
    final EditText passwordEditText = (EditText) findViewById(R.id.loginPassword);

    //get the strings from edittext fields.
    String email = emailEditText.getText().toString();
    String password = passwordEditText.getText().toString();

    //debugging
    Log.v("EditText", emailEditText.getText().toString());
    Log.v("EditText", passwordEditText.getText().toString());

    //check for user input
    if (isEmpty(emailEditText) || isEmpty(passwordEditText)) {
        Toast.makeText(MainActivity.this.getBaseContext(),
                "Please complete all fields.", Toast.LENGTH_SHORT).show();
        return;
    } else {
        //do some magic to see if the password and username match...
        //if they match then send an intent to the home activity

        User userResult = db.getUser(email, password);
        //Log.v("UserRes getUser(email):", userResult.getEmail());
        // Log.v("UserRes getUser(px):", userResult.getPassword());
        if (userResult.getEmail() == null) {
            Toast.makeText(MainActivity.this.getBaseContext(),
                    "Username or password invalid.", Toast.LENGTH_SHORT).show();
            return;
        } else {
            Toast.makeText(MainActivity.this.getBaseContext(),
                    "Success.", Toast.LENGTH_SHORT).show();
            Log.d("user MA: ", userResult.toString());
            Intent intent;
            intent = new Intent(MainActivity.this, HomeActivity.class);
            intent.putExtra("User_Object", userResult);
            MainActivity.this.startActivity(intent);
        }
    }
    db.closeDB();
}
}

最后是我要接收用户对象的 HomeActivity 类:

公共(public)类 HomeActivity 扩展了 AppCompatActivity {

private User thisUser;//want this to be private!!

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

    User user;
    Bundle bundle = getIntent().getExtras();
    Intent i = getIntent();

    user = (User) i.getParcelableExtra("User_Object");
    User newUser = bundle.getParcelable("User_Object");

    Log.d("user HA PE: ", newUser.toString());
    Log.d("user HA B: ", user.toString());
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_home, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * method called to instantiate a new intent to go to viewScoreActivity screen.
 * @param view
 */
public void viewScoresLink(View view){
    Intent intent;
    intent = new Intent(HomeActivity.this, ViewScoreActivity.class);
    intent.putExtra("User_Object", thisUser);
    HomeActivity.this.startActivity(intent);
}

/**
 * method called to instantiate a new intent to go to the submitScoreActiviyt screen.
 * @param view
 */
public void addNewScoreLink(View view){
    Intent intent;
    intent = new Intent(HomeActivity.this, AddScoreActivity.class);
    intent.putExtra("User_Object", thisUser);
    HomeActivity.this.startActivity(intent);
}

public void logout(View view){
    Intent intent;
    intent = new Intent(HomeActivity.this, MainActivity.class);
    HomeActivity.this.startActivity(intent);
}

我在运行时没有得到任何异常。对象字段都是空的

Answer 1

这是因为您为 User 重载了私有(private)构造函数。不要创建该类的私有(private)实例。将其更改为:

private User(Parcel in) {
    setName(in.readString());
    setEmail(in.readString());
    setAge(in.readInt());
    setWeight(in.readInt());
    setHeight(in.readInt());
    setId(in.readLong());
}