Question

我尝试在AndroidStudio中创建一个值为＆＃34; nome＆＃34;的ListView。我为此创建了一个列表和一个适配器，但我的应用程序无法识别变量＆＃34; services＆＃34;。

这是我的活动代码

public class MainActivity extends AppCompatActivity {
    private String service;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView listView = (ListView) findViewById(R.id.list_item1);


        ArrayAdapter<Services> servicesAdapter = new ArrayAdapter<Services>(this, android.R.layout.simple_list_item_1, services); <-- in this line
        listView.setAdapter(servicesAdapter);

    }


    private List<Services> gerarServices(){
        List<Services> services  = new ArrayList<Services>();
        services.add(criarServices("Home"));
        services.add(criarServices("Delivery"));

        return services;
    }

    private Services criarServices(String nome){
        Services service = new Services(nome);
        return service;
    }
}

有什么建议吗？提前谢谢！

Answer 1

services变量不在onCreate方法的范围内。正如@ Code-Apprentice所提到的，您可能想要了解有关局部变量范围的更多信息。

因此，您可能想要做的是在gerarServices()方法中调用onCreate方法并将其分配给本地变量，然后将其传递给ArrayAdapter。像这样：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ListView listView = (ListView) findViewById(R.id.list_item1);

    List<Services> services = gerarServices();


    ArrayAdapter<Services> servicesAdapter = new ArrayAdapter<Services>(this, android.R.layout.simple_list_item_1, services);
    listView.setAdapter(servicesAdapter);

}

或

@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ListView listView = (ListView) findViewById(R.id.list_item1); ArrayAdapter<Services> servicesAdapter = new ArrayAdapter<Services>(this, android.R.layout.simple_list_item_1, gerarServices()); listView.setAdapter(servicesAdapter); }

希望它有所帮助！

Answer 2

在您的代码中，我没有看到任何声明和初始化services的方法但gerarServices()会返回Services列表。所以我想你必须在使用任何变量或类实例之前做上述操作像这样，

ListView listView = (ListView) findViewById(R.id.list_item1);

// Add this line of code
List<Services> services = gerarServices();

ArrayAdapter<Services> servicesAdapter = new ArrayAdapter<Services>(this, android.R.layout.simple_list_item_1, services);

希望得到这个帮助。

Java无法识别ListView变量

2 个答案: