我已经使用ListView控件实现了一个下载应用程序但是当我运行应用程序时，我收到NullPointerException错误。
我的代码如下::
public class TestDownload extends Activity {
private ListView lstView;
private ImageAdapter imageAdapter;
// private Handler handler = new Handler();
ArrayList<Url_Dto> list = new ArrayList<Url_Dto>();
File download;
public static final int DIALOG_DOWNLOAD_THUMBNAIL_PROGRESS = 0;
String strDownloaDuRL;
ArrayList<HashMap<String, Object>> MyArrList = new ArrayList<HashMap<String, Object>>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test_download);
new LoadContentFromServer().execute();
}
public void ShowThumbnailData() {
// ListView and imageAdapter
lstView = (ListView) findViewById(R.id.listView1);
lstView.setClipToPadding(false);
list = DBAdpter.getUrl_Detail();
imageAdapter = new ImageAdapter(getApplicationContext());
lstView.setAdapter(imageAdapter);
}
public void startDownload(final int position) {
Runnable runnable = new Runnable() {
int Status = 0;
public void run() {
String urlDownload = MyArrList.get(position)
.get("VideoPathThum").toString();
Log.v("log_tag", "urlDownload ::: " + urlDownload);
int count = 0;
try {
URL url = new URL(urlDownload);
URLConnection conexion = url.openConnection();
conexion.connect();
int lenghtOfFile = conexion.getContentLength();
Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);
InputStream input = new BufferedInputStream(
url.openStream());
// Get File Name from URL
String fileName = urlDownload.substring(
urlDownload.lastIndexOf('/') + 1,
urlDownload.length());
download = new File(
Environment.getExternalStorageDirectory()
+ "/download/");
if (!download.exists()) {
download.mkdir();
}
strDownloaDuRL = download + "/" + fileName;
OutputStream output = new FileOutputStream(strDownloaDuRL);
byte data[] = new byte[1024];
long total = 0;
while ((count = input.read(data)) != -1) {
total += count;
Status = (int) ((total * 100) / lenghtOfFile);
output.write(data, 0, count);
// Update ProgressBar
/*
* handler.post(new Runnable() { public void run() {
* updateStatus(position, Status); } });
*/
TestDownload.this.runOnUiThread(new Runnable() {
public void run() {
updateStatus(position, Status);
}
});
}
output.flush();
output.close();
input.close();
} catch (Exception e) {
}
}
};
new Thread(runnable).start();
}
private void updateStatus(int index, int Status) {
View v = lstView.getChildAt(index - lstView.getFirstVisiblePosition());
// Update ProgressBar
ProgressBar progress = (ProgressBar) v.findViewById(R.id.progressBar);
progress.setProgress(Status);
// Update Text to ColStatus
TextView txtStatus = (TextView) v.findViewById(R.id.ColStatus);
txtStatus.setPadding(10, 0, 0, 0);
txtStatus.setText("Load : " + String.valueOf(Status) + "%");
// Enabled Button View
if (Status >= 100) {
Button btnView = (Button) v.findViewById(R.id.btnView);
btnView.setTextColor(Color.RED);
btnView.setEnabled(true);
}
}
class LoadContentFromServer extends AsyncTask<Object, Integer, Object> {
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected Object doInBackground(Object... params) {
HashMap<String, Object> map;
String url = "http://imprintingdesign.com/hiren_testing/TestHopeNew/testHope/data/url.json";
String result = "";
InputStream is = null;
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
// http post
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(url);
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
}
try {
BufferedReader reader = new BufferedReader(
new InputStreamReader(is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
try {
JSONObject json_obj = new JSONObject(result);
JSONArray j_Arr_fn = json_obj.getJSONArray("children");
for (int i = 0; i < j_Arr_fn.length(); i++) {
JSONObject json_objs = j_Arr_fn.getJSONObject(i);
Url_Dto proDto = new Url_Dto();
proDto.url_video = json_objs.getString("videoUrl");
map = new HashMap<String, Object>();
map.put("VideoPathThum", proDto.url_video);
MyArrList.add(map);
}
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
}
return null;
}
@Override
protected void onPostExecute(Object result) {
ShowThumbnailData();
}
}
class ImageAdapter extends BaseAdapter {
private Context mContext;
public ImageAdapter(Context context) {
mContext = context;
}
public int getCount() {
return MyArrList.size();
}
public Object getItem(int position) {
return MyArrList.get(position);
}
public long getItemId(int position) {
return position;
}
public View getView(final int position, View convertView,
ViewGroup parent) {
// TODO Auto-generated method stub
View view = null;
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) mContext
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view = inflater.inflate(R.layout.activity_column, null);
final ViewHolder viewHolder = new ViewHolder();
viewHolder.imageView = (ImageView) view
.findViewById(R.id.ColImgPath);
viewHolder.txtStatus = (TextView) view
.findViewById(R.id.ColStatus);
viewHolder.txtHidden = (TextView) view.findViewById(R.id.Txtv);
viewHolder.btnDownload = (Button) view
.findViewById(R.id.btnDownload);
viewHolder.btnView = (Button) view.findViewById(R.id.btnView);
viewHolder.progress = (ProgressBar) view
.findViewById(R.id.progressBar);
// ColImage
viewHolder.imageView.getLayoutParams().height = 110;
viewHolder.imageView.getLayoutParams().width = 110;
viewHolder.imageView.setPadding(10, 10, 10, 10);
viewHolder.imageView
.setScaleType(ImageView.ScaleType.CENTER_CROP);
try {
viewHolder.imageView
.setImageResource(list.get(position).images[position]);
} catch (Exception e) {
// When Error
viewHolder.imageView
.setImageResource(android.R.drawable.ic_menu_report_image);
}
viewHolder.txtStatus.setPadding(10, 0, 0, 0);
viewHolder.txtStatus.setText("...");
viewHolder.txtHidden.setVisibility(View.GONE);
viewHolder.txtHidden.setText(String.valueOf(position));
viewHolder.btnDownload.setTextColor(Color.RED);
viewHolder.btnDownload
.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Download
viewHolder.btnDownload.setEnabled(false);
viewHolder.btnDownload.setTextColor(Color.GRAY);
startDownload(position);
}
});
viewHolder.btnView.setEnabled(false);
viewHolder.btnView.setTextColor(Color.GRAY);
viewHolder.btnView
.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
ViewVideoDelete(position);
viewHolder.btnDownload.setEnabled(true);
updateStatus(position, 0);
}
});
viewHolder.progress.setPadding(10, 0, 0, 0);
viewHolder.imageView.setTag(MyArrList.get(position));
viewHolder.txtStatus.setTag(MyArrList.get(position));
viewHolder.txtHidden.setTag(MyArrList.get(position));
viewHolder.btnDownload.setTag(MyArrList.get(position));
viewHolder.btnView.setTag(MyArrList.get(position));
viewHolder.progress.setTag(MyArrList.get(position));
view.setTag(viewHolder);
} else {
view = convertView;
((ViewHolder) view.getTag()).imageView.setTag(MyArrList
.get(position));
((ViewHolder) view.getTag()).txtStatus.setTag(MyArrList
.get(position));
((ViewHolder) view.getTag()).txtHidden.setTag(MyArrList
.get(position));
((ViewHolder) view.getTag()).btnDownload.setTag(MyArrList
.get(position));
((ViewHolder) view.getTag()).btnView.setTag(MyArrList
.get(position));
((ViewHolder) view.getTag()).progress.setTag(MyArrList
.get(position));
}
ViewHolder holder = (ViewHolder) view.getTag();
holder.imageView.getLayoutParams().height = 110;
holder.imageView.getLayoutParams().width = 110;
holder.imageView.setPadding(10, 10, 10, 10);
holder.imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
try {
holder.imageView
.setImageResource(list.get(position).images[position]);
} catch (Exception e) {
// When Error
holder.imageView
.setImageResource(android.R.drawable.ic_menu_report_image);
}
holder.txtStatus.setPadding(10, 0, 0, 0);
holder.txtStatus.setText("...");
holder.txtHidden.setVisibility(View.GONE);
holder.txtHidden.setText(String.valueOf(position));
holder.btnDownload.setTextColor(Color.RED);
holder.btnView.setEnabled(false);
holder.btnView.setTextColor(Color.GRAY);
holder.progress.setPadding(10, 0, 0, 0);
return convertView;
}
}
static class ViewHolder {
protected ImageView imageView;
protected TextView txtStatus;
protected TextView txtHidden;
protected Button btnDownload;
protected Button btnView;
protected ProgressBar progress;
}
public void ViewVideoDelete(int position) {
String urlDownload = MyArrList.get(position).get("VideoPathThum")
.toString();
String fileName = urlDownload.substring(
urlDownload.lastIndexOf('/') + 1, urlDownload.length());
download = new File(Environment.getExternalStorageDirectory()
+ "/download/");
String strPath = download + "/" + fileName;
Log.v("log_tag", "fileNameDElete :: " + strPath);
File delete = new File(strPath);
delete.delete();
}
}
我使用Main Xml Code ::
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/tableLayout1"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<LinearLayout
android:id="@+id/main_lay"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:background="#437654" >
<Button
android:id="@+id/all_btn"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="BACk" />
<TextView
android:id="@+id/accepted_all"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="DownLoad Video" />
<Button
android:id="@+id/not_shown"
android:layout_width="100dip"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="All DOwnload" />
</LinearLayout>
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0.1"
android:orientation="horizontal" >
<ListView
android:id="@+id/listView1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:focusable="false" >
</ListView>
</LinearLayout>
</LinearLayout>
我使用了Custome Xml List View Row ::
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:descendantFocusability="blocksDescendants"
android:orientation="horizontal" >
<ImageView
android:id="@+id/ColImgPath"
android:layout_width="50dp"
android:layout_height="50dp" />
<TextView
android:id="@+id/Txtv"
android:layout_width="50dp"
android:layout_height="50dp"
android:visibility="gone"
/>
<TableLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TableRow
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dip" >
<TextView
android:id="@+id/ColStatus"
android:text="Status"
android:textAppearance="?android:attr/textAppearanceSmall" />
<ProgressBar
android:id="@+id/progressBar"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="100dp"
android:layout_height="wrap_content" />
</TableRow>
<TableRow
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dip" >
<Button
android:id="@+id/btnDownload"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Download" />
<Button
android:id="@+id/btnView"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Delete" />
</TableRow>
</TableLayout>
</LinearLayout>
当我运行App NOt Start但在下面获取错误时：
03-08 10:51:59.757: E/AndroidRuntime(549): FATAL EXCEPTION: main
03-08 10:51:59.757: E/AndroidRuntime(549): java.lang.NullPointerException
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.AbsListView.obtainView(AbsListView.java:1432)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.ListView.measureHeightOfChildren(ListView.java:1216)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.ListView.onMeasure(ListView.java:1127)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.View.measure(View.java:8313)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:701)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.onMeasure(LinearLayout.java:311)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.View.measure(View.java:8313)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:701)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.onMeasure(LinearLayout.java:311)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.View.measure(View.java:8313)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.View.measure(View.java:8313)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.measureVertical(LinearLayout.java:531)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.View.measure(View.java:8313)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.View.measure(View.java:8313)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.ViewRoot.performTraversals(ViewRoot.java:839)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.view.ViewRoot.handleMessage(ViewRoot.java:1859)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.os.Handler.dispatchMessage(Handler.java:99)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.os.Looper.loop(Looper.java:130)
03-08 10:51:59.757: E/AndroidRuntime(549): at android.app.ActivityThread.main(ActivityThread.java:3683)
03-08 10:51:59.757: E/AndroidRuntime(549): at java.lang.reflect.Method.invokeNative(Native Method)
03-08 10:51:59.757: E/AndroidRuntime(549): at java.lang.reflect.Method.invoke(Method.java:507)
03-08 10:51:59.757: E/AndroidRuntime(549): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-08 10:51:59.757: E/AndroidRuntime(549): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-08 10:51:59.757: E/AndroidRuntime(549): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
当ListAdapter.getView方法返回null时会发生这种情况。在这种情况下，我看到您的ImageAdapter课程正在返回convertView，可能是null。我认为这意味着要返回view而不是convertView。
答案 1 :(得分：0)
尝试以下方式，
public View getView(final int position, View convertView,
ViewGroup parent) {
// TODO Auto-generated method stub
View view = null;
if (convertView == null) {
......
view.setTag(viewHolder);
} else {
view = convertView;
...
}
ViewHolder holder = (ViewHolder) view.getTag();
.....
return convertView; // if convertView == null , where convertView is instanced??
}
}