如何使用viewHolder模式让UI元素在listView中保持滚动？

Question

我正在研究使用 viewHolder 模式来使我的 UI 元素在列表视图滚动时不会重置为默认值。调查之后我不知道如何处理这个问题。我什至不确定我现有的代码是否允许我使用 viewHolder 模式。我是初学者，所以请详细说明，不要跳过细节。谢谢你

MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.app.Activity;
import android.view.KeyEvent;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ViewSwitcher;

import java.util.ArrayList;

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final ArrayList<String> Chores = new ArrayList<>();
        Chores.add("");

        final ListAdapter MyAdapter = new CustomAdapter(this, Chores);
        ListView listViewObject = (ListView)findViewById(R.id.customListView_ID);
        listViewObject.setAdapter(MyAdapter);

        listViewObject.setOnItemClickListener(
            new AdapterView.OnItemClickListener(){
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id){
                    String ChoreString = String.valueOf(parent.getItemAtPosition(position));
                }
            }

        );
        final Button button = (Button) findViewById(R.id.button_ID);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Chores.add("");
                ((ArrayAdapter)MyAdapter).notifyDataSetChanged();
            }
        });
    }
}

自定义适配器.java

import android.content.Context;
import android.content.DialogInterface;
import android.support.annotation.NonNull;
import android.support.v7.app.AlertDialog;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.ArrayList;

import static com.example.emilythacker.chorelist.R.id.textView_ID;

class CustomAdapter extends ArrayAdapter{

    public CustomAdapter(Context context, ArrayList choreText) {
        super(context, R.layout.custon_listview_row, choreText);
    }

    @NonNull
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater myInflater = LayoutInflater.from(getContext());
        View customView = myInflater.inflate(R.layout.custon_listview_row, parent, false);

        ImageButton imageButton = (ImageButton) customView.findViewById(R.id.imageButton_ID);
        final TextView textView = (TextView) customView.findViewById(textView_ID);

        textView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //what happens when textView is clicked
                AlertDialog alertDialog = new AlertDialog.Builder(getContext()).create();
                final EditText input = new EditText(getContext());
                input.setHint("hint");
                alertDialog.setView(input);
                alertDialog.setTitle("Set Chore");
                alertDialog.setMessage("Alert message to be shown");
                alertDialog.setButton(AlertDialog.BUTTON_NEUTRAL, "OK", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {

                                //this will set text to "hello" only if user does not enter anything into input
                                //textView.setText("hello");

                                //this also will only work if there is no input entered into input...which will change textView into empty space
                                textView.setText(input.getText().toString());

                                //works the same with or without dialog.dismiss();
                                dialog.dismiss();
                            }
                        });
                alertDialog.show();
            }
        });
        imageButton.setImageResource(R.drawable.clock);
        return customView;
    }
}

Answer 1

我发现这个教程在学习使用 ViewHolder 模式时非常有用。它在解释如何使用它时非常清楚，但如果您感到困惑，请随时询问。

Answer 2

当您对任何列表项执行某些更改时，我们应该调用notifyDataSetChanged()，以便列表视图得到更新。

回答你的问题： 更新文本后，在textview.onClickListener()方法中调用notifyDataSetChanged()。

最好切换到 RecyclerView，在这种情况下，当我们添加新项目时，我们可以只调用 notificationItemAdded(position) ，它只会刷新该位置的视图，而不刷新整个视图。 当我们更新任何项目时，我们可以调用notifyItemChanged(position)。