Java 单击所选按钮后，applicaton已停止显示logcat错误
在我的应用程序中，我将动态提供复选框，并在我提供的“获取选定项”按钮上方提供复选框，如果您单击该按钮，它将获取我们在列表视图中提供的已检查数据。但现在，单击“按钮选择”后，应用程序已停止 Mainactivity.javaJava 单击所选按钮后，applicaton已停止显示logcat错误,java,android,Java,Android,在我的应用程序中，我将动态提供复选框，并在我提供的“获取选定项”按钮上方提供复选框，如果您单击该按钮，它将获取我们在列表视图中提供的已检查数据。但现在，单击“按钮选择”后，应用程序已停止 Mainactivity.java public class MainActivity extends Activity implements FetchDataListener,OnClickListener { private static final int ACTIVITY_CREATE=0;
public class MainActivity extends Activity implements FetchDataListener,OnClickListener
{
private static final int ACTIVITY_CREATE=0;
private ProgressDialog dialog;
ListView lv;
private List<Application> items;
private Button btnGetSelected;
//private ProjectsDbAdapter mDbHelper;
//private SimpleCursorAdapter dataAdapter;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list_item);
//mDbHelper = new ProjectsDbAdapter(this);
//mDbHelper.open();
//fillData();
//registerForContextMenu(getListView());
lv =(ListView)findViewById(R.id.list);
btnGetSelected = (Button) findViewById(R.id.btnget);
btnGetSelected.setOnClickListener(this);
initView();
}
private void initView()
{
// show progress dialog
dialog = ProgressDialog.show(this, "", "Loading...");
String url = "http://dry-brushlands-3645.herokuapp.com/posts.json";
FetchDataTask task = new FetchDataTask(this);
task.execute(url);
//mDbHelper.open();
//Cursor projectsCursor = mDbHelper.fetchAllProjects();
//startManagingCursor(projectsCursor);
// Create an array to specify the fields we want to display in the list (only TITLE)
//String[] from = new String[]{ProjectsDbAdapter.KEY_TITLE};
// and an array of the fields we want to bind those fields to (in this case just text1)
//int[] to = new int[]{R.id.text1};
/* Now create a simple cursor adapter and set it to display
SimpleCursorAdapter projects =
new SimpleCursorAdapter(this, R.layout.activity_row, projectsCursor, from, to);
setListAdapter(projects);
*/
// create the adapter using the cursor pointing to the desired data
//as well as the layout information
/*dataAdapter = new SimpleCursorAdapter(
this, R.layout.activity_row,
projectsCursor,
from,
to,
0);
setListAdapter(dataAdapter);
*/
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
//getMenuInflater().inflate(R.menu.activity_main, menu);
super.onCreateOptionsMenu(menu);
MenuInflater mi = getMenuInflater();
mi.inflate(R.menu.activity_main, menu);
return true;
}
@Override
public boolean onMenuItemSelected(int featureId, MenuItem item) {
createProject();
return super.onMenuItemSelected(featureId, item);
}
private void createProject() {
Intent i = new Intent(this, ProjectEditActivity.class);
startActivityForResult(i, ACTIVITY_CREATE);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
super.onActivityResult(requestCode, resultCode, intent);
initView();
}
@Override
public void onFetchComplete(List<Application> data)
{
// dismiss the progress dialog
if ( dialog != null )
dialog.dismiss();
// create new adapter
ApplicationAdapter adapter = new ApplicationAdapter(this, data);
// set the adapter to list
lv.setAdapter(adapter);
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
CheckBox chk = (CheckBox) view.findViewById(R.id.checkbox);
Application bean = items.get(position);
if (bean.isSelected()) {
bean.setSelected(false);
chk.setChecked(false);
} else {
bean.setSelected(true);
chk.setChecked(true);
}
}
});
}
// Toast is here...
private void showToast(String msg) {
Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
}
@Override
public void onFetchFailure(String msg)
{
// dismiss the progress dialog
if ( dialog != null )
dialog.dismiss();
// show failure message
Toast.makeText(this, msg, Toast.LENGTH_LONG).show();
}
@Override
public void onClick(View v) {
StringBuffer sb = new StringBuffer();
// Retrive Data from list
for (Application bean : items) {
if (bean.isSelected()) {
sb.append(bean.getContent());
sb.append(",");
}
}
showAlertView(sb.toString().trim());
}
private void showAlertView(String str) {
AlertDialog alert = new AlertDialog.Builder(this).create();
if (TextUtils.isEmpty(str)) {
alert.setTitle("Not Selected");
alert.setMessage("No One is Seleceted!!!");
} else {
// Remove , end of the name
String strContactList = str.substring(0, str.length() - 1);
alert.setTitle("Selected");
alert.setMessage(strContactList);
}
alert.setButton("Ok", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
alert.show();
}
@Override
public void onBackPressed() {
AlertDialog alert_back = new AlertDialog.Builder(this).create();
alert_back.setTitle("Quit?");
alert_back.setMessage("Are you sure want to Quit?");
alert_back.setButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
alert_back.setButton2("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
MainActivity.this.finish();
}
});
alert_back.show();
}
@Override
public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
// TODO Auto-generated method stub
}
public class Application {
private String content;
private boolean selected;
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public boolean isSelected() {
return selected;
}
public void setSelected(boolean selected) {
this.selected = selected;
}
}
public class FetchDataTask extends AsyncTask<String, Void, String>
{
private final FetchDataListener listener;
private String msg;
public FetchDataTask(FetchDataListener listener)
{
this.listener = listener;
}
@Override
protected String doInBackground(String... params)
{
if ( params == null )
return null;
// get url from params
String url = params[0];
try
{
// create http connection
HttpClient client = new DefaultHttpClient();
HttpGet httpget = new HttpGet(url);
// connect
HttpResponse response = client.execute(httpget);
// get response
HttpEntity entity = response.getEntity();
if ( entity == null )
{
msg = "No response from server";
return null;
}
// get response content and convert it to json string
InputStream is = entity.getContent();
return streamToString(is);
}
catch ( IOException e )
{
msg = "No Network Connection";
}
return null;
}
@Override
protected void onPostExecute(String sJson)
{
if ( sJson == null )
{
if ( listener != null )
listener.onFetchFailure(msg);
return;
}
try
{
// convert json string to json object
JSONObject jsonObject = new JSONObject(sJson);
JSONArray aJson = jsonObject.getJSONArray("post");
// create apps list
List<Application> apps = new ArrayList<Application>();
for ( int i = 0; i < aJson.length(); i++ )
{
JSONObject json = aJson.getJSONObject(i);
Application app = new Application();
app.setContent(json.getString("content"));
// add the app to apps list
apps.add(app);
}
//notify the activity that fetch data has been complete
if ( listener != null )
listener.onFetchComplete(apps);
}
catch ( JSONException e )
{
e.printStackTrace();
msg = "Invalid response";
if ( listener != null )
listener.onFetchFailure(msg);
return;
}
}
/**
* This function will convert response stream into json string
*
* @param is
* respons string
* @return json string
* @throws IOException
*/
public String streamToString(final InputStream is) throws IOException
{
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try
{
while ( (line = reader.readLine()) != null )
{
sb.append(line + "\n");
}
}
catch ( IOException e )
{
throw e;
}
finally
{
try
{
is.close();
}
catch ( IOException e )
{
throw e;
}
}
return sb.toString();
}
}
公共类FetchDataTask扩展了AsyncTask
{
私有最终获取数据侦听器；
私有字符串msg；
公共FetchDataTask（FetchDataListener侦听器）
{
this.listener=listener；
}
@凌驾
受保护的字符串doInBackground（字符串…参数）
{
if（params==null）
返回null；
//从参数获取url
字符串url=params[0]；
尝试
{
//创建http连接
HttpClient=new DefaultHttpClient（）；
HttpGet HttpGet=新的HttpGet（url）；
//连接
HttpResponse response=client.execute（httpget）；
//得到回应
HttpEntity=response.getEntity（）；
if（实体==null）
{
msg=“服务器无响应”；
返回null；
}
//获取响应内容并将其转换为json字符串
InputStream=entity.getContent（）；
返回streamToString（is）；
}
捕获（IOE异常）
{
msg=“无网络连接”；
}
返回null；
}
@凌驾
受保护的void onPostExecute（字符串sJson）
{
if（sJson==null）
{
if（侦听器！=null）
onFetchFailure（msg）；
返回；
}
尝试
{
//将json字符串转换为json对象
JSONObject JSONObject=新的JSONObject（sJson）；
JSONArray aJson=jsonObject.getJSONArray（“post”）；
//创建应用程序列表
列表应用程序=新建ArrayList（）；
对于（int i=0；i06-04 10:07:49.857:E/AndroidRuntime（2454）：java.lang.NullPointerException
06-04 10:07:49.857:E/AndroidRuntime（2454）：在com.example.jsonandroid.MainActivity.onClick（MainActivity.java:174）这个错误很明显，您在onClick上有一个nullPointerException，请检查这一行：
applicationbean:items for (Application bean : items) {
...
}
private ArrayList<Application> items = new ArrayList<Application>();
private ArrayList items=new ArrayList（）；
然后在列表中有一些数据来执行必要的操作 假设
onFetchCompletefor (Application bean : items) {
@Override
public void onFetchComplete(List<Application> data) {
this.items = data;
@覆盖
公共void onFetchComplete（列表数据）{
此项=数据；
但是如果看不到所有代码，就很难判断发生了什么。MainActivity第174行是什么？省去了我们将整个内容复制并粘贴到文本编辑器/idefor（应用程序bean:items）中的麻烦{这是一行显示错误的代码，你能看到我在上面的代码中是这样初始化的吗，比如这个私有列表项；这不是初始化，只是声明。这样做不会为此分配内存。我不能在你的代码中任何地方添加我要求你添加的行。私有列表项=新列表（）；将解决空指针异常。但是，如果希望执行for循环中的代码，则需要将类型为“application”的数据添加到项目（列表）中。如果我添加的代码无法实例化类型列表，则会显示如下错误，in=new“list”在列表中，它显示了我上面提到的所有代码，你可以看到我的所有代码，告诉Dude你必须初始化项，并且当你指向列表的位置时确保你有数据为什么我们使用该代码，该代码的功能是什么，它是用html标记获取的，但是我提到没有html标记，你可以在我的适配器类别中看到该代码打开一个新问题-应用程序已停止
for (Application bean : items) {
@Override
public void onFetchComplete(List<Application> data) {
this.items = data;