我开始一项新活动后，ListView减少了

Question

我是使用CustomAdapter创建ListViews的新手（这是我的第一次尝试），我不确定我做得多好/高效。所以我想要做的就是在ListView中获得突出显示为红色的名称。我使用getSelectedName方法执行此操作。但是，在BuildInput类中，当我想要MainActivity并且意图回到BuildInput类时，ListView完全消失了。由于ListView已经消失，突出显示的红色名称和getSelectedName方法也不起作用。

当我打算使用MainActivity时，如何防止ListView进行减少？

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类创建的内容：

您在edittext中键入名称，然后单击确认将名称添加到列表视图并清除edittext。当您单击列表视图中的名称时，它将突出显示红色，并且该名称是我需要在MainActivity类中使用的名称。

Answer 1

我在您的代码中进行了一些更改：

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

当你想要MainActivity并且没有完成BoardInputActivity时，当MainActivity关闭时，ListView仍然存在。但是当你想要BoardInputActivity时，一切都将被重建，包括适配器。