Question

我希望适配器更改微调器上的textview并更改主活动的背景imageview。如果我可以制作一个适配器来接收具有这两种品质的物体（宠物），但我不确定如何。 pet对象有一个字符串用于pet的名称和url用于downloadImage asyncTask我现在的问题是我得到一个空指针异常。构造函数也让我感到困惑。我只是不认为适配器正在做它应该做的事情。这就是我现在这样做的方式：

public class CustomAdapter extends ArrayAdapter<String> {

//for layouts
LayoutInflater myInflater;
private ArrayList<String> list;
private ArrayList<String> names;

//
public static class ViewHolder {
    ImageView img1;
    TextView tv1;
    String url;
    Bitmap bitmap;
}

//generate data we use

// private final MainActivity mainActivity;
String tempUrl;

public CustomAdapter(Context context, int textViewResourceId, ArrayList<String> names, ArrayList<String> pets) {
    super(context, textViewResourceId, pets);

    myInflater = ((Activity) context).getLayoutInflater();


    this.names = names;
    list = pets;
    tempUrl = "http://tetonsoftware.com/pets/";

}

@Override
public int getCount() {
    return list.size();
}


@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder = null;
    if (convertView == null) {
        convertView = myInflater.inflate(R.layout.spinner_item, null);

        holder = new ViewHolder();
        holder.img1 = (ImageView) convertView.findViewById(R.id.imageView);
        holder.tv1 = (TextView) convertView.findViewById(R.id.textview);
        convertView.setTag(holder);
    } else
        holder = (ViewHolder) convertView.getTag();

    //set the text
    holder.tv1.setText(names.get(position));
    holder.url = tempUrl.concat(list.get(position));

    //start a thread to download image

    new DownloadImageTask(holder).execute(holder.url);
    //new ImageDownloader().execute(holder);

    return convertView;
}

}

public class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {

private static final String TAG = "DownloadImageTask";

private static final int DEFAULTBUFFERSIZE = 50;
private static final int NODATA = -1;
private final CustomAdapter.ViewHolder myVH;

private String url;
private ImageView imageView;
private Drawable placeholder;


public DownloadImageTask(CustomAdapter.ViewHolder myVH) {
    this.myVH = myVH;
    this.url = myVH.url;
}




@Override
protected Bitmap doInBackground(String... params) {

    // site we want to connect to
    String url = params[0];

    // note streams are left willy-nilly here because it declutters the
    // example
    try {
        URL url1 = new URL(url);

        // this does no network IO
        HttpURLConnection connection = (HttpURLConnection) url1.openConnection();

        // can further configure connection before getting data
        // cannot do this after connected
        // connection.setRequestMethod("GET");
        connection.setReadTimeout(500);
        connection.setConnectTimeout(500);

        // this opens a connection, then sends GET & headers
        connection.connect();

        // lets see what we got make sure its one of
        // the 200 codes (there can be 100 of them
        // http_status / 100 != 2 does integer div any 200 code will = 2
        int statusCode = connection.getResponseCode();
        if (statusCode / 100 != 2) {
            return null;
        }

        // get our streams, a more concise implementation is
        // BufferedInputStream bis = new
        // BufferedInputStream(connection.getInputStream());
        InputStream is = connection.getInputStream();
        BufferedInputStream bis = new BufferedInputStream(is);

        // the following buffer will grow as needed
        ByteArrayOutputStream baf = new ByteArrayOutputStream(DEFAULTBUFFERSIZE);
        //ByteArrayBuffer baf = new ByteArrayBuffer(DEFAULTBUFFERSIZE);
        int current = 0;

        // wrap in finally so that stream bis is sure to close
        try {
            while ((current = bis.read()) != NODATA) {
                baf.write((byte) current);
            }

            // convert to a bitmap
            byte[] imageData = baf.toByteArray();
            return BitmapFactory.decodeByteArray(imageData, 0, imageData.length);
        } finally {
            // close resource no matter what exception occurs
            bis.close();
        }
    } catch (IOException exc) {
        return null;
    }
}

@Override
protected void onPostExecute(Bitmap result) {

    Log.d(TAG, "Result for " + url);
    if (result != null) {

        if (url == this.myVH.url) {
            Log.d(TAG, "SUCCESS for " + url);
            this.myVH.img1.setImageBitmap(result);
        }
        else
            Log.d(TAG, "FAIL url != this.myVH.url for " + url);
    } else
        Log.d(TAG, "NULL for " + url);

}

}

这是错误消息：

04-02 19：55：37.252 10941-10941 / com.example.arya.project3 E / AndroidRuntime：FATAL EXCEPTION：main 处理：com.example.arya.project3，PID：10941 java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void android.widget.ImageView.setImageBitmap（android.graphics.Bitmap）' at com.example.arya.project3.DownloadImageTask.onPostExecute（DownloadImageTask.java:106）在com.example.arya.project3.DownloadImageTask.onPostExecute（DownloadImageTask.java:17）在android.os.AsyncTask.finish（AsyncTask.java:636）在android.os.AsyncTask.access $ 500（AsyncTask.java:177）在android.os.AsyncTask $ InternalHandler.handleMessage（AsyncTask.java:653）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:135）在android.app.ActivityThread.main（ActivityThread.java:5468） at java.lang.reflect.Method.invoke（Native Method）在java.lang.reflect.Method.invoke（Method.java:372）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:976）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:771） 04-02 19：55：37.253 10941-10941 / com.example.arya.project3 I / AndroidRuntime：向activityManagerService报告FATAL 04-02 19：55：37.364 10941-10941 / com.example.arya.project3 I / AndroidRuntime：完成向activityManagerService报告FATAL 04-02 19：55：37.364 10941-10941 / com.example.arya.project3 I / Process：发送信号。 PID：10941 SIG：9

如何为微调器

0 个答案: