开始新活动后，ListView 会减少

Question

我是使用 CustomAdapters 制作 ListViews 的新手（这是我的第一次尝试），但我不确定我做得如何/效率如何。所以我要做的是获取在 ListView 中以红色突出显示的名称。我使用 getSelectedName 方法执行此操作。但是，在 BuildInput 类中，当我意图返回 MainActivity 并意图返回 BuildInput 类时，ListView 完全消失了。由于 ListView 消失了，突出显示的红色名称也消失了，getSelectedName 方法也不起作用。

当我打算使用 MainActivity 时，如何防止 ListView 减少？

public class Names {
    public String name;
    public Names(){
        super();
    }
    public Names(String name){
        super();
        this.name = name;

-

public class CustomAdapter extends ArrayAdapter<Names>{

private ArrayList<Names> items;
private TextView tvHolder;
private String selectedName = "";

public CustomAdapter (Context context, ArrayList<Names> items){
    super(context, 0, items);
    this.items = items;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    Names names = getItem(position);
    if(convertView == null)
    {
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.item_namechoices, parent, false);

    }
    Names nm = items.get(position);
    if (nm != null){
        final TextView tv = (TextView)convertView.findViewById(R.id.nameItem);
        tv.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (tvHolder != null) {
                    tvHolder.setBackgroundColor(Color.WHITE);
                    v.setBackgroundColor(Color.RED);
                    tvHolder = tv;
                    selectedName = tv.getText().toString();
                } else {
                    v.setBackgroundColor(Color.RED);
                    tvHolder = tv;
                    selectedName = tv.getText().toString();
                }
            }
        });
    }
    TextView tv = (TextView)convertView.findViewById(R.id.nameItem);
    tv.setText(names.name);
    return convertView;
}

public String getSelectedName(){
    return selectedName;
}
}

-

public class BoardInput extends Activity {

private EditText mUserInput;
private Button mConfirm;
private Button mReady;
private ArrayList<Names> arrayOfNames = new ArrayList<Names>();
private CustomAdapter adapter;
private ListView listview;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_boardinput);

    adapter = new CustomAdapter(BoardInput.this, arrayOfNames);
    listview = (ListView) findViewById(R.id.listview);
    listview.setAdapter(adapter);

    mUserInput = (EditText) findViewById(R.id.nameInput);
    mConfirm = (Button) findViewById(R.id.confirm);
    mConfirm.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (mUserInput.getText().toString().equals("")) {
                Toast.makeText(getApplicationContext(), "Please enter a name.", Toast.LENGTH_SHORT);
            } else {
                arrayOfNames.add(new Names(mUserInput.getText().toString()));
                mUserInput.setText("");
                adapter = new CustomAdapter(BoardInput.this, arrayOfNames);
                listview = (ListView) findViewById(R.id.listview);
                listview.setAdapter(adapter);
            }

        }
    });
    mReady = (Button) findViewById(R.id.ready);
    mReady.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {
            if (adapter.getSelectedName().isEmpty()){
                Log.d("NULL","NULL");
            }
            else{
                Log.d("BoardInput", adapter.getSelectedName());
                Intent i = new Intent(BoardInput.this, MainActivity.class);
                startActivity(i);
            }
        }
    });

}

这是 BoardInput 类创建的：

您在编辑文本中输入名称并单击确认会将名称添加到列表视图并清除编辑文本。当您单击列表视图中的名称时，它将突出显示红色，这就是我需要在 MainActivity 类中使​​用的名称。

Answer 1

我对您的代码进行了一些更改：

public class BoardInput extends Activity {

private EditText mUserInput;
private Button mConfirm;
private Button mReady;
private List<String> names = new ArrayList<>();
private ArrayList<Names> arrayOfNames = new ArrayList<Names>();
private CustomAdapter adapter;
private ListView listview;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_boardinput);

    adapter = new CustomAdapter(BoardInput.this, arrayOfNames);
    listview = (ListView) findViewById(R.id.listview);
    listview.setAdapter(adapter);

    mUserInput = (EditText) findViewById(R.id.nameInput);
    mConfirm = (Button) findViewById(R.id.confirm);
    mConfirm.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (mUserInput.getText().toString().equals("")) {
                Toast.makeText(getApplicationContext(), "Please enter a name.", Toast.LENGTH_SHORT);
            } else {
                arrayOfNames.add(new Names(mUserInput.getText().toString()));
                mUserInput.setText("");
    **Edited**:
                adapter.notifyDataSetChanged();
    listview.invalidateView();
            }

        }
    });
    mReady = (Button) findViewById(R.id.ready);
    mReady.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {
            if (adapter.getSelectedName().isEmpty()){
                Log.d("NULL","NULL");
            }
            else{
                Log.d("BoardInput", adapter.getSelectedName());
                Intent i = new Intent(BoardInput.this, MainActivity.class);
                startActivity(i);
            }
        }
    });

}

Answer 2

当您打算进入 MainActivity 而没有完成 BoardInputActivity 时，当 MainActivity 关闭时，ListView 仍然存在。但是，当您打算使用 BoardInputActivity 时，所有内容都将被重建，包括适配器。