android - 保存自定义对象的 ArrayList 并向 ArrayList 添加新对象

Question

我在将自定义对象的 ArrayList 实例保存在 Activity 中，然后在另一个 Activity 中执行某些操作后检索它时遇到问题。在第一个 Activity (具有 ArrayList)内，有一个启动第二个 Activity 的按钮。在第二个 Activity 中，要求用户创建一个新对象，该对象随后将添加到第一个 Activity 的 ArrayList 中，以便当第二个 Activity 完成时，第一个 Activity 再次显示所有对象的 ListView(包括最后一个一个创建)。我面临的问题是，只有最后创建的对象显示在 ListView 中。

这是第一个 Activity 的代码:

public class CargasMin extends AppCompatActivity implements View.OnClickListener {

RelativeLayout rl_CargasMin;

ImageButton bt_AdDep;
Button bt_CalcCargas;

ListView listView_Dep;

ArrayList<Dependencia> listaDeDependencias = new ArrayList<Dependencia>();

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

    rl_CargasMin = (RelativeLayout) findViewById(R.id.cargasMinLayout);

    bt_AdDep = (ImageButton) findViewById(R.id.bt_AdDep_CargasMin);
    bt_CalcCargas = (Button) findViewById(R.id.bt_CalcCargas_CargasMin);
    bt_AdDep.setOnClickListener(this);
    bt_CalcCargas.setOnClickListener(this);

    // This seems not to be working!
    if(savedInstanceState == null) { }
    else {
        listaDeDependencias = savedInstanceState.getParcelableArrayList("key");
    }

    // Get last object created
    Intent intent_de_AdDep = getIntent();
    Dependencia dependenciaAAdicionar = (Dependencia) intent_de_AdDep.getParcelableExtra("novaDependencia");
    if(dependenciaAAdicionar == null) { }
    else {
        listaDeDependencias.add(dependenciaAAdicionar);
    }

    //Cria Adapter pra mostrar dependencias na ListView
    DependenciaAdapter adapterDeDependencias = new DependenciaAdapter(this, R.layout.adapter_dependencia, listaDeDependencias);

    //Seta Adapter
    listView_Dep = (ListView) findViewById(R.id.listView_Dep_CargasMin);
    listView_Dep.setAdapter(adapterDeDependencias);
}


@Override
public void onClick(View v) {
    switch(v.getId()) {
        case R.id.bt_AdDep_CargasMin:
            Intent intent_AdDep = new Intent(CargasMin.this, AdDep.class);
            startActivity(intent_AdDep);
            break;
        case R.id.bt_CalcCargas_CargasMin:
            //
            break;
    }
}


@Override
protected void onSaveInstanceState(Bundle outState) {
    // Aqui se salva a listaDeDependencias quando a Atividade eh momentaneamente fechada.
    outState.putParcelableArrayList("key", listaDeDependencias);
    super.onSaveInstanceState(outState);
    }
}

这是我的自定义类 Dependencia 的代码:

public class Dependencia implements Parcelable {
String nome;
int tipo;

float largura = 0;
float comprimento = 0;
float area = 0;
float perimetro = 0;

// Constructor da classe Dependencia.
public Dependencia(String nomeDep, int tipoDep) {
    nome = nomeDep;
    tipo = tipoDep;
}

private Dependencia(Parcel in) {
    nome = in.readString();
    tipo = in.readInt();
    largura = in.readFloat();
    comprimento = in.readFloat();
    area = in.readFloat();
    perimetro = in.readFloat();
}

public int describeContents() {
    return 0;
}

public void writeToParcel(Parcel out, int flags) {
    out.writeString(nome);
    out.writeInt(tipo);
    out.writeFloat(largura);
    out.writeFloat(comprimento);
    out.writeFloat(area);
    out.writeFloat(perimetro);
}

public static final Parcelable.Creator<Dependencia> CREATOR = new Parcelable.Creator<Dependencia>() {
    public Dependencia createFromParcel(Parcel in) {
        return new Dependencia(in);
    }

    public Dependencia[] newArray(int size) {
        return new Dependencia[size];
    }
};
}

这是第二个 Activity 的代码:

public class AdDep extends AppCompatActivity implements View.OnClickListener {

RelativeLayout rl_AdDep;

EditText et_Nome;
EditText et_Largura;
EditText et_Comprimento;
EditText et_Area;
EditText et_Perimetro;

Spinner spinner_Tipo;
String vetorTipo[];
int tipoEscolhido;

Button bt_AdDep1;
Button bt_AdDep2;

Dependencia novaDependencia;

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

    rl_AdDep = (RelativeLayout)findViewById(R.id.adDepLayout);

    et_Nome = (EditText) findViewById(R.id.et_Nome_AdDep);
    et_Largura = (EditText) findViewById(R.id.et_Largura_AdDep);
    et_Comprimento = (EditText) findViewById(R.id.et_Comprimento_AdDep);
    et_Area = (EditText) findViewById(R.id.et_Area_AdDep);
    et_Perimetro = (EditText) findViewById(R.id.et_Perimetro_AdDep);

    spinner_Tipo = (Spinner) findViewById(R.id.spinner_Tipo_AdDep);

    bt_AdDep1 = (Button) findViewById(R.id.bt_AdDep1);
    bt_AdDep2 = (Button) findViewById(R.id.bt_AdDep2);


    // Adicionando opcoes no spinner
    vetorTipo = new String[5];
    vetorTipo[0] = "Banheiro";
    vetorTipo[1] = "Varanda";
    vetorTipo[2] = "Cozinha/Copa/Serviço/etc.";
    vetorTipo[3] = "Sala/Dormitório";
    vetorTipo[4] = "Outro";

    // Criando ArrayAdapter de strings pro spinner
    ArrayAdapter<String> adapterTipo = new ArrayAdapter<String>(AdDep.this, android.R.layout.simple_spinner_item, vetorTipo);

    // Setando o Adapter
    spinner_Tipo.setAdapter(adapterTipo);

    // Valor default do spinner (hint)
    spinner_Tipo.setSelection(0);


    bt_AdDep1.setOnClickListener(this);
    bt_AdDep2.setOnClickListener(this);
}


@Override
public void onClick(View v) {
    if(String.valueOf(spinner_Tipo.getSelectedItem()).equals("Banheiro"))
        tipoEscolhido = 1;
    else if(String.valueOf(spinner_Tipo.getSelectedItem()).equals("Varanda"))
        tipoEscolhido = 2;
    else if(String.valueOf(spinner_Tipo.getSelectedItem()).equals("Cozinha/Copa/Serviço/etc."))
        tipoEscolhido = 3;
    else if(String.valueOf(spinner_Tipo.getSelectedItem()).equals("Sala/Dormitório"))
        tipoEscolhido = 4;
    else if(String.valueOf(spinner_Tipo.getSelectedItem()).equals("Outro"))
        tipoEscolhido = 5;

    novaDependencia = new Dependencia(et_Nome.getText().toString(), tipoEscolhido);

    switch(v.getId()) {
        case R.id.bt_AdDep1:
            novaDependencia.largura = Float.valueOf(et_Largura.getText().toString());
            novaDependencia.comprimento = Float.valueOf(et_Comprimento.getText().toString());
            break;
        case R.id.bt_AdDep2:
            novaDependencia.area = Float.valueOf(et_Area.getText().toString());
            novaDependencia.perimetro = Float.valueOf(et_Perimetro.getText().toString());
            break;
    }

    AlertDialog.Builder builder2 = new AlertDialog.Builder(v.getContext());
    builder2.setMessage("Deseja adicionar T.U.E. nesta dependência?").setPositiveButton("Sim", dialogClickListener).setNegativeButton("Não", dialogClickListener).show();
}

// Objeto tipo dialog criado para perguntar se usario deseja inserir TUEs
DialogInterface.OnClickListener dialogClickListener = new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {
        switch (which){
            case DialogInterface.BUTTON_POSITIVE:
                //Yes button clicked
                break;
            case DialogInterface.BUTTON_NEGATIVE:
                Intent intent_NovaDep_CargasMin = new Intent(AdDep.this, CargasMin.class);
                intent_NovaDep_CargasMin.putExtra("novaDependencia", novaDependencia);
                startActivity(intent_NovaDep_CargasMin);
                break;
        }
    }
};

}

如果有人知道如何解决这个问题，请分享。谢谢。

Answer 1

问题是您正在从 AdDep Activity 启动 CargasMin Activity 的新实例。您的 AdDep Activity 应该刚刚完成并将结果返回到返回堆栈上的 CargasMin Activity 的现有实例，以便您也可以查看所有之前的列表数据。

要从 AdDep 中检索新列表项作为结果，请使用 startActivityForResult()

case R.id.bt_AdDep_CargasMin:
    Intent intent_AdDep = new Intent(CargasMin.this, AdDep.class);
    startActivityForResult(intent_AdDep, ADD_DEP_REQUEST);
    break;

ADD_DEP_REQUEST 只是一个请求代码常量

public static final int ADD_DEP_REQUEST = 1;

现在，当 AdDep 收集完数据后，它会返回新的数据项作为结果。

case DialogInterface.BUTTON_NEGATIVE:
    Intent result = new Intent();
    result.putExtra("novaDependencia", novaDependencia);
    setResult(Activity.RESULT_OK, result);
    finish();
    break;

您的主要 CargasMin Activity 随后将接收新数据项作为

 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
     if (requestCode == ADD_DEP_REQUEST) {
         if (resultCode == RESULT_OK) {
             // Get last object created
             Dependencia dependenciaAAdicionar =
                         (Dependencia) data.getParcelableExtra("novaDependencia");
             if(dependenciaAAdicionar != null){
                 listaDeDependencias.add(dependenciaAAdicionar);
                 // Refresh Adapter pra mostrar dependenciaAAdicionar na ListView
                 adapterDeDependencias.notifyDataSetChanged();
             }
         }
     }
 }

请注意，listaDeDependencias 和 adapterDeDependencias 已更改为 Activity 的实例成员。

如果您将数据持久化到某个存储(例如在文件或数据库中)，您当前的方法会奏效，但仍然不建议创建 CargasMin 的新实例，因为返回堆栈就足够了。