java - 如何在 ListView 中通知数据集正确更改

Question

我正在开发聊天应用程序，用户可以在其中发送短信和图像当数据集中只有文本消息时，我使用 ListView 来实现此目的， ListView 以正确的方式显示正确的数据，当用户发送图像时，图像正确添加到列表中，而当我调用通知数据集更改时，数据集位置发生变化，例如图像添加在 0 显示在 3 或第四名

package com.exception.chatapp;

import java.util.ArrayList;
import java.util.HashMap;
import android.content.Context;
import android.net.Uri;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.TextView;

public class ChatAdapter extends BaseAdapter {

Context context;
ArrayList<HashMap<String, String>> data;
LayoutInflater inflator;
String imageurl = "http://www.example.com/webservices/";

public ChatAdapter(Context context, ArrayList<HashMap<String, String>> data) {
    this.context = context;
    this.data = data;
    inflator = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    // return data.size();
    return data.size();
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return position;
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return position;
}

@Override
public View getView(int position, View convertview, ViewGroup parentview) {
    // TODO Auto-generated method stub

    ViewHolder holder;
    if (convertview == null) {
        convertview = inflator.inflate(R.layout.chat_item, parentview,false);
        holder = new ViewHolder();
        holder.message = (TextView) convertview
                .findViewById(R.id.txtusermessage);
        holder.userimage = (ImageView) convertview
                .findViewById(R.id.userimage);
        convertview.setTag(holder);
    } else {
        holder = (ViewHolder) convertview.getTag();
    }
    holder.userimage.setVisibility(View.GONE);
    HashMap<String, String> map = data.get(position);
    if (!map.get("user_name").equals("me")) {
        if (map.get("type").equals("text")) {
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT);
            params.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
            holder.message.setLayoutParams(params);
            holder.message.requestLayout();
            holder.message.setText(map.get("message"));
            holder.message.setBackgroundResource(R.drawable.farhan_blue);
        } else if (map.get("type").equals("image")) {
            holder.userimage.setVisibility(View.VISIBLE);
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    200,
                    200);
            params.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
            holder.userimage.setLayoutParams(params);
            holder.userimage.requestLayout();
            holder.userimage.setBackgroundResource(R.drawable.farhan_blue);
            holder.message.setVisibility(View.GONE);
            ImageLoader loader = new ImageLoader(context);
            Log.d("image_url", imageurl + map.get("image_url"));
            loader.DisplayImage(imageurl + map.get("image_url"),
                    holder.userimage);
        } else if (map.get("type").equals("gps")) {
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT);
            params.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
            holder.message.setLayoutParams(params);
            holder.message.requestLayout();
            holder.message.setText(map.get("lat") + "," + map.get("lng"));
            holder.message.setBackgroundResource(R.drawable.farhan_blue);
        }

        else if (map.get("type").equals("contact")) {
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT);
            params.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
            holder.message.setLayoutParams(params);
            holder.message.requestLayout();
            holder.message.setText(map.get("name") + "\n"
                    + map.get("number"));
            holder.message.setBackgroundResource(R.drawable.farhan_blue);
        }
    } else {
        if (map.get("type").equals("text")) {
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT);
            params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
            holder.message.setLayoutParams(params);
            holder.message.requestLayout();
            holder.message.setText(map.get("message"));
            holder.message.setBackgroundResource(R.drawable.farhan_white);
        } else if (map.get("type").equals("image")) {
            holder.message.setVisibility(View.GONE);
            holder.userimage.setVisibility(View.VISIBLE);
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    200,
                    200);
            params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
            holder.userimage.setLayoutParams(params);
            holder.userimage.requestLayout();
            holder.userimage.setBackgroundResource(R.drawable.farhan_white);


            if (map.get("from") != null) {
                Log.d("image_url",map.get("image_url"));
                holder.userimage
                        .setImageURI(Uri.parse(map.get("image_url")));
            } else {
                ImageLoader loader = new ImageLoader(context);
                Log.d("image_url", imageurl + map.get("image_url"));
                loader.DisplayImage(imageurl + map.get("image_url"),
                        holder.userimage);
            }

        }

        else if (map.get("type").equals("gps")) {
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT);
            params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
            holder.message.setLayoutParams(params);
            holder.message.requestLayout();
            holder.message.setText(map.get("lat") + "," + map.get("lng"));
            holder.message.setBackgroundResource(R.drawable.farhan_white);
        } else if (map.get("type").equals("contact")) {
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT);
            params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
            holder.message.setLayoutParams(params);
            holder.message.requestLayout();
            holder.message.setText(map.get("name") + "\n"
                    + map.get("number"));
            holder.message.setBackgroundResource(R.drawable.farhan_white);
        }

    }

    return convertview;
}

static class ViewHolder {
    TextView message;
    ImageView userimage;
}

}

这是我的 ListView ，我将宽度和高度设置为 match_parent，同时位于布局 xml 中两个布局的上方和下方

<ListView
    android:id="@+id/list"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_above="@+id/chatlayout"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/linearLayout1"
    android:divider="@null"
    android:dividerHeight="0dp"
    android:stackFromBottom="true" >
</ListView>

根据 Activity 结果，我将图像添加到 ListView

if (resultCode == RESULT_OK && requestCode == 1 && data1!=null) {   
        try {

            Uri selectedImage = data1.getData();
            filepath = getRealPathFromURI(selectedImage);
            Log.d("path", filepath);
            ChatItem item = new ChatItem();
            item.setUsername("me");
            item.setMessage("");
            item.setType("image");
            item.setImage_uri(filepath);
            item.setFrom("local");
            data.add(item);
            adapter.notifyDataSetChanged();
            list.smoothScrollToPosition(data.size() - 1);
            message.setText("");
            new UploadFile().execute(filepath, id, rid, "image");

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

Answer 1

根据您的描述和提供的代码，我认为问题是由您使用条件切换 View 布局的方式以及 ListView 中存在的一些内部优化的方式发生冲突引起的。

ListView 经过优化，可以回收以前膨胀的 View 。这样做的目的是避免为每个项目增加新的布局。这种回收，与您用来选择项目类型的逻辑相结合 - 显示和隐藏每个项目的不同子元素 - 可能是此问题的原因，因为当您添加图片时，可能不会创建新 View ，您只是更新旧的。

我会做什么，我会改变切换项目 View 的方式，以便每种类型的 View 都有不同的模型对象 - 例如消息对象、图像对象等。然后我将按以下方式设置适配器

View v = convertView;
Object o = data.get(position);
LayoutInflaer inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

if(o != null){
    if(o instanceof ImageMessage){
        if(v == null){
            v = inflater.inflate(R.layout.image_message);
        }
        createImageMessagView(v, (ImageMessage) o);
    } else if (o instanceOf textMessage){
        // handle different object type
    }

其中createImageMes​​sageView是您可以通过id找到相关布局 subview 并设置其内容的地方。

此方法允许您为每个项目类使用不同的布局。这样，您就不会创建一个 View ，将其存储在 View 持有者中，然后稍后尝试修改其内容。相反，您正在扩充自定义布局(如果尚不存在)，该布局旨在显示该项目类型的内容。