Android viewholder class 范围广

Question

我有一个使用 viewholder 模式的列表适配器，我的问题是我需要在同一 class 中包含的 AsyncTask 的 onpostexecute() 中从 viewholder 更新 TextView，但这总是 returns TextView 上的空指针，如何从 viewholder 给我的 textviews 提供足够的范围，以便我可以在 AsyncTask 中更改它们？我将在下面包含一个代码示例，在此先感谢

public class ListAdapter extends BaseAdapter {


TextView tvA1, tvA2;

Integer submitId;
String submitQuestion;

public ListAdapter() {

  ....

}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    friendsViewHolder holder = null;


    if (convertView == null) {

        holder = new friendsViewHolder();

        convertView = inflater.inflate(R.layout.list_item_status, null);


        holder.tvA1 = (TextView) convertView
                .findViewById(R.id.tvA1);
        holder.tvA2 = (TextView) convertView
                .findViewById(R.id.tvA2);
        holder.btQ1 = (LinearLayout) convertView
                .findViewById(R.id.btConfirm);
        holder.btQ2 = (LinearLayout) convertView
                .findViewById(R.id.btDeny);



        convertView.setTag(holder);
    } else {
        holder = (friendsViewHolder) convertView.getTag();
    }


    tvA1 = holder.tvA1;
    tvA2 = holder.tvA2;

    holder.btQ1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            submitId = id;
            submitQuestion = q1;

            new UpdateAnswer().execute();


        }
    });

    holder.btQ2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            submitId = id;
            submitQuestion = q2;

            new UpdateAnswer().execute();

        }
    });

    return convertView;


}

static class friendsViewHolder {

    TextView tvA1, tvA2;
    LinearLayout btQ1, btQ2;

}

private class UpdateAnswer extends AsyncTask<Void, Void, ArrayList<Object>> {


    @Override
    protected ArrayList<Object> doInBackground(Void... params) {

        return apiHelper.submitAnswer(submitId, submitQuestion);

    }

    @Override
    protected void onPostExecute(ArrayList<Object> answers) {
        super.onPostExecute(answers);

        if (answers != null) {

            Integer a1 = (Integer) answers.get(1);
            Integer a2 = (Integer) answers.get(2);

            //Error here
            tvA1.setText(a1);
            tvA1.setVisibility(View.VISIBLE);

            //error here
            tvA2.setText(a2);
            tvA2.setVisibility(View.VISIBLE);


        }

    }
}
}

Answer 1

Java 是按值传递，但您可以在值中发送对象的引用。我已经使用了上面的内容，并将 holder 的引用发送给了 AsyncTask。

public class ListAdapter extends BaseAdapter {


TextView tvA1, tvA2;

Integer submitId;
String submitQuestion;

public ListAdapter() {

  ....

}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    friendsViewHolder holder = null;


    if (convertView == null) {

        holder = new friendsViewHolder();

        convertView = inflater.inflate(R.layout.list_item_status, null);


        holder.tvA1 = (TextView) convertView
                .findViewById(R.id.tvA1);
        holder.tvA2 = (TextView) convertView
                .findViewById(R.id.tvA2);
        holder.btQ1 = (LinearLayout) convertView
                .findViewById(R.id.btConfirm);
        holder.btQ2 = (LinearLayout) convertView
                .findViewById(R.id.btDeny);



        convertView.setTag(holder);
    } else {
        holder = (friendsViewHolder) convertView.getTag();
    }


    holder.btQ1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            submitId = id;
            submitQuestion = q1;

            new UpdateAnswer(holder).execute();


        }
    });

    holder.btQ2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            submitId = id;
            submitQuestion = q2;

            new UpdateAnswer().execute();

        }
    });

    return convertView;


}

static class friendsViewHolder {

    TextView tvA1, tvA2;
    LinearLayout btQ1, btQ2;

}

private class UpdateAnswer extends AsyncTask<Void, Void, ArrayList<Object>> {
     friendsViewHolder holder;

    UpdateAnswer(friendsViewHolder holder)
    {
        this.holder = holder;
    }

    @Override
    protected ArrayList<Object> doInBackground(Void... params) {

        return apiHelper.submitAnswer(submitId, submitQuestion);

    }

    @Override
    protected void onPostExecute(ArrayList<Object> answers) {
        super.onPostExecute(answers);

        if (answers != null) {

            Integer a1 = (Integer) answers.get(1);
            Integer a2 = (Integer) answers.get(2);

            //Error here
            holder.tva1.setText(a1);
            holder.tva1.setVisibility(View.VISIBLE);

            //error here
            holder.tva2.setText(a2);
            holder.tva2.setVisibility(View.VISIBLE);


        }

    }
}
}

Answer 2

让我们在这里和那里改变一些东西:)

让我们交朋友ViewHolder public，我还需要在java中添加它以某种方式自定义命名类，名称以驼峰字母开头，只需将FirstLetterOfEeachWordIsBig :)

让我们将构造函数添加到更新任务:)

private class UpdateAnswer extends AsyncTask<Void, Void, ArrayList<Object>> {
    int submitId;
    String submitQuestion;
    friendsViewHolder holder;

    public UpdateAnswer (int submitId, String submitQuestion, friendsViewHolder holder) {
        this.submitId = submitId;
        this.submitQuestion = submitQuestion;
        this.holder = holder;
    }

点击让我们更改为

  final frendsViewHolder finalHolder = holder;
  holder.btQ1.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        new UpdateAnswer(id, q1, finalHolder).execute();
    }
});

我们不再需要全局 TvA1、tvA2、submitId、submitQuestion；

最后我们需要编辑 onPostExecute，但是我认为这很难，因为您已经转发了 holder 值 :)

        holder.tvA1.setText(a1);
        holder.tvA1.setVisibility(View.VISIBLE);

        holder.tvA2.setText(a2);
        holder.tvA2.setVisibility(View.VISIBLE);

在 java 中，您可以创建构造函数以允许将其他数据传递给对象，我们使用它来为我们的任务设置 id、问题和持有人，并且为了将该信息传递给其他对象，我们不应该这样做使用全局值（每个进程都可以更改它们），考虑您的呼叫 "apiHelper.submitAnswer(submitId, submitQuestion)" 需要很长时间才能继续（例如半秒）的情况，然后用户在半秒内首先点击答案并回答c 关于第 3 个问题，通过全局传递值，您无法确定接受哪个答案:)

干杯:)

Android viewholder class 范围广

Android viewholder class wide scope

java

android

android-viewholder