java - 如何让 Android 旋转器处于 Activity 状态？

Question

我是 Android 编程新手，下面的代码将使最终用户选择他想要查看的部分并显示 ListView 。我无法使微调器处于 Activity 状态，即使我选择不同的部分，它也只显示一个 ListView 。

public class TeacherClasses extends AppCompatActivity implements AdapterView.OnItemClickListener,View.OnClickListener{
public String[] Section1 = {"Bonilla, Abbie", "Hernando, Roland Joseph", "Ko, Kritofer", "Manaig, Kathleen",
        "Olalia, Jerome","Rosario, Kyle", "Sevilla, Karen", "Tancioco, Eron", "Villena, Mark" };
public String[] Section2 = {"Chavez, Stephanie", "Espana, Bren Alfred", "Faro, Ede", "Gonzales, Venice",
        "Magora, Joshua James","Roman, Jairah", "Ramirez, Stephanie", "Tiboli, Jamalul", "Torrazo, Nicole" };
public String[] Section3 = {"Arbonida, Caye Anne", "De Guzman, Patricia", "Escandor, Jennifer", "Marzan, Rann",
        "Menorca, Paula","Payofelin, Marlo", "Pimentel, Iris Coleen", "Queen, Elizabeth", "Unggoy, Monkey" };
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_teacher_classes);
    Button btn_Sections = (Button) findViewById(R.id.btn_Sections);
    btn_Sections.setOnClickListener(this);
    CreateList();
}
private void CreateList() {

    Spinner spn_Sections = (Spinner) findViewById(R.id.spn_Sections);
    List<String> Sections = new ArrayList<String>();
    Sections.add("Section 1");
    Sections.add("Section 2");
    Sections.add("Section 3");

    ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item,Sections);
    dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spn_Sections.setAdapter(dataAdapter);


    ListAdapter ClassAdapter = null;
    String s = spn_Sections.getSelectedItem().toString();
    if (s.equals("Section 1")) {
        ClassAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, Section1);
        Toast.makeText(this, "Section 1", Toast.LENGTH_SHORT).show();
    } else if (s.equals("Section 2")) {
        ClassAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, Section2);
        Toast.makeText(this, "Section 2", Toast.LENGTH_SHORT).show();
    } else if (s.equals("Section 3")) {
        ClassAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, Section3);
        Toast.makeText(this, "Section 3", Toast.LENGTH_SHORT).show();
    }
    ListView MyClasses = (ListView)findViewById(R.id.list_ClassList);
    MyClasses.setAdapter(ClassAdapter);
    MyClasses.setOnItemClickListener(this);


}

Answer 1

试试这个方法:

private void CreateList() {

    Spinner spn_Sections = (Spinner) findViewById(R.id.spn_Sections);
    List<String> Sections = new ArrayList<String>();
    Sections.add("Section 1");
    Sections.add("Section 2");
    Sections.add("Section 3");

    ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, Sections);
    dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spn_Sections.setAdapter(dataAdapter);


    spn_Sections.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

            switch (position) {
                case 0:
                    ClassAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, Section1);
                    Toast.makeText(getApplicationContext(), "Section 1", Toast.LENGTH_SHORT).show();
                    break;
                case 1:
                    ClassAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, Section2);
                    Toast.makeText(getApplicationContext(), "Section 2", Toast.LENGTH_SHORT).show();
                    break;
                case 2:
                    ClassAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, Section3);
                    Toast.makeText(getApplicationContext(), "Section 3", Toast.LENGTH_SHORT).show();
                    break;
            }
        }

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

            // sometimes you need nothing here
        }
    });

    ListView MyClasses = (ListView) findViewById(R.id.list_ClassList);
    MyClasses.setAdapter(ClassAdapter);
    MyClasses.setOnItemClickListener(this);

}

您必须为spinner设置setOnItemSelectedListener监听器

同时全局声明；

ListAdapter ClassAdapter = null;