Java.lang.Classcast Exception : java. lang.String cannot be cast to error in android 问题

Question

我正在开发 listview 应用程序，在此 Activity 中我使用了一个搜索框，但是当我在搜索框中输入文本时，出现错误 Java.lang.Classcast Exception: java.lang.String cannot be cast to

Activity

public class ConnectActivity extends Activity {

    // unsorted list items
    List<Company> mItems;

    // array list to store section positions
    ArrayList<Integer> mListSectionPos;

    // array list to store listView data
    ArrayList<String> mListItems;

    // custom list view with pinned header
    PinnedHeaderListView mListView;

    // custom adapter
    PinnedHeaderAdapter mAdaptor;

    // search box
    EditText mSearchView;

    // loading view
    ProgressBar mLoadingView;

    // empty view
    TextView mEmptyView;



    @SuppressWarnings("unchecked")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        overridePendingTransition(R.anim.activity_open_translate,
                R.anim.activity_close_scale);

        // UI elements
        setupViews();

        mListSectionPos = new ArrayList<Integer>();
        mListItems = new ArrayList<String>();

        // for handling configuration change
        if (savedInstanceState != null) {
            mListItems = savedInstanceState.getStringArrayList("mListItems");
            mListSectionPos = savedInstanceState
                    .getIntegerArrayList("mListSectionPos");

            if (mListItems != null && mListItems.size() > 0
                    && mListSectionPos != null && mListSectionPos.size() > 0) {
                setListAdaptor();
            }

            String constraint = savedInstanceState.getString("constraint");
            if (constraint != null && constraint.length() > 0) {
                mSearchView.setText(constraint);
                setIndexBarViewVisibility(constraint);
            }
        } else {
            new Poplulate().execute(mItems);
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        // closing transition animations
        overridePendingTransition(R.anim.activity_open_scale,
                R.anim.activity_close_translate);
    }

    private void setupViews() {
        setContentView(R.layout.activity_connect);
        mSearchView = (EditText) findViewById(R.id.search_view);
        mLoadingView = (ProgressBar) findViewById(R.id.loading_view);
        mListView = (PinnedHeaderListView) findViewById(R.id.list_view);
        mListView.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                TextView selectedCompanyName = (TextView) view.findViewById(R.id.row_title);
                Toast.makeText(getApplicationContext(), selectedCompanyName.getText().toString(), Toast.LENGTH_SHORT).show();
                Company selectedCopmanyData = new Select().from(Company.class).where("Company_Name = ?", selectedCompanyName.getText().toString().trim()).executeSingle();
                startActivity(new Intent(ConnectActivity.this, CompanyActivity.class).putExtra("SELECTED_COMPANY", selectedCopmanyData));
            }
        });
        mEmptyView = (TextView) findViewById(R.id.empty_view);

        //mItems = new Select().from(Company.class).where("Bookmark = ?", true).orderBy("Company_Name ASC").execute();
        mItems = new Select().from(Company.class).orderBy("Company_Name ASC").execute();

        if (mItems.size() == 0) {
            Company sampleData1 = new Company();
            sampleData1.companyName = "MahenCO";
            sampleData1.companyId = new Long(new SimpleDateFormat("ddMMyyyyHHmmSS").format(new Date()));
            sampleData1.groupId = new Integer(1);
            sampleData1.groupName = "Finance";
            sampleData1.customerSupportNo = "12345678";
            sampleData1.customerWebSite = "http://www.mahenco.com";
            sampleData1.customerSupportEmail = "customersupport@mahenco.com";
            sampleData1.bookmarked = false;
            sampleData1.save();

            Company sampleData2 = new Company();
            sampleData2.companyName = "ECG Ltd";
            sampleData2.companyId = new Long(new SimpleDateFormat("ddMMyyyyHHmmSS").format(new Date()));
            sampleData2.groupId = new Integer(1);
            sampleData2.groupName = "Insurance";
            sampleData2.customerSupportNo = "18002666";
            sampleData2.customerWebSite = "http://www.ecg.com";
            sampleData2.customerSupportEmail = "customersupport@ecg.com";
            sampleData2.bookmarked = true;
            sampleData2.save();

            mItems = new Select().from(Company.class).orderBy("Company_Name ASC").execute();
        }
    }

    // I encountered an interesting problem with a TextWatcher listening for
    // changes in an EditText.
    // The afterTextChanged method was called, each time, the device orientation
    // changed.
    // An answer on Stackoverflow let me understand what was happening: Android
    // recreates the activity, and
    // the automatic restoration of the state of the input fields, is happening
    // after onCreate had finished,
    // where the TextWatcher was added as a TextChangedListener.The solution to
    // the problem consisted in adding
    // the TextWatcher in onPostCreate, which is called after restoration has
    // taken place
    //
    // http://stackoverflow.com/questions/6028218/android-retain-callback-state-after-configuration-change/6029070#6029070
    // http://stackoverflow.com/questions/5151095/textwatcher-called-even-if-text-is-set-before-adding-the-watcher
    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        mSearchView.addTextChangedListener(filterTextWatcher);
        super.onPostCreate(savedInstanceState);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.connect, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        default:
            return super.onOptionsItemSelected(item);
        }

    }

    @Override
    public void onOptionsMenuClosed(Menu menu) {
        openOptionsMenu();
    }

    private void setListAdaptor() {
        // create instance of PinnedHeaderAdapter and set adapter to list view
        mAdaptor = new PinnedHeaderAdapter(this, mListItems, mListSectionPos);
        mListView.setAdapter(mAdaptor);

        LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);

        // set header view
        View pinnedHeaderView = inflater.inflate(R.layout.section_row_view,
                mListView, false);
        mListView.setPinnedHeaderView(pinnedHeaderView);

        // set index bar view
        IndexBarView indexBarView = (IndexBarView) inflater.inflate(
                R.layout.index_bar_view, mListView, false);
        indexBarView.setData(mListView, mListItems, mListSectionPos);
        mListView.setIndexBarView(indexBarView);

        // set preview text view
        View previewTextView = inflater.inflate(R.layout.preview_view,
                mListView, false);
        mListView.setPreviewView(previewTextView);

        // for configure pinned header view on scroll change
        mListView.setOnScrollListener(mAdaptor);
    }

    private TextWatcher filterTextWatcher = new TextWatcher() {
        public void afterTextChanged(Editable s) {
            String str = s.toString();
            if (mAdaptor != null && str != null)
                mAdaptor.getFilter().filter(str);
        }

        public void beforeTextChanged(CharSequence s, int start, int count,
                int after) {
        }

        public void onTextChanged(CharSequence s, int start, int before,
                int count) {

        }
    };

然后我进入了我的 listFilter。这是过滤器类

public class ListFilter extends Filter {
        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            // NOTE: this function is *always* called from a background thread,
            // and
            // not the UI thread.
            String constraintStr = constraint.toString().toLowerCase(
                    Locale.getDefault());
            FilterResults result = new FilterResults();

            if (constraint != null && constraint.toString().length() > 0) {
                ArrayList<String> filterItems = new ArrayList<String>();

                synchronized (this) {
                    for (int i = 0; i < mItems.size(); i++) {
                        String item = mItems.get(i).companyName;
                        if (item.toLowerCase(Locale.getDefault()).startsWith(
                                constraintStr)) {
                            filterItems.add(item);
                        }
                    }
                    result.count = filterItems.size();
                    result.values = filterItems;
                }
            } else {
                synchronized (this) {
                    result.count = mItems.size();
                    result.values = mItems;
                }
            }
            return result;
        }

        @SuppressWarnings("unchecked")
        @Override
        protected void publishResults(CharSequence constraint,
                FilterResults results) {
            List<Company> filtered = (List<Company>) results.values;
            setIndexBarViewVisibility(constraint.toString());
            // sort array and extract sections in background Thread
            new Poplulate().execute(filtered);
        }

    }

    private void setIndexBarViewVisibility(String constraint) {
        // hide index bar for search results
        if (constraint != null && constraint.length() > 0) {
            mListView.setIndexBarVisibility(false);
        } else {
            mListView.setIndexBarVisibility(true);
        }
    }

    // sort array and extract sections in background Thread here we use
    // AsyncTask
    private class Poplulate extends AsyncTask<List<Company>, Void, Void> {

        private void showLoading(View contentView, View loadingView,
                View emptyView) {
            contentView.setVisibility(View.GONE);
            loadingView.setVisibility(View.VISIBLE);
            emptyView.setVisibility(View.GONE);
        }

        private void showContent(View contentView, View loadingView,
                View emptyView) {
            contentView.setVisibility(View.VISIBLE);
            loadingView.setVisibility(View.GONE);
            emptyView.setVisibility(View.GONE);
        }

        private void showEmptyText(View contentView, View loadingView,
                View emptyView) {
            contentView.setVisibility(View.GONE);
            loadingView.setVisibility(View.GONE);
            emptyView.setVisibility(View.VISIBLE);
        }

        @Override
        protected void onPreExecute() {
            // show loading indicator
            showLoading(mListView, mLoadingView, mEmptyView);
            super.onPreExecute();
        }

        @Override
        protected Void doInBackground(List<Company>... params) {
            mListItems.clear();
            mListSectionPos.clear();
            List<Company> items = params[0];
            if (mItems.size() > 0) {

                // NOT forget to sort array
                // No need for sort as it has already sorted while feathing from database
                //Collections.sort(items.);

                int i = 0;
                String prev_section = "";
                while (i < items.size()) {
                    String current_item = items.get(i).companyName;
                    String current_section = current_item.substring(0, 1)
                            .toUpperCase(Locale.getDefault());

                    if (!prev_section.equals(current_section)) {
                        mListItems.add(current_section);
                        mListItems.add(current_item);
                        // array list of section positions
                        mListSectionPos
                                .add(mListItems.indexOf(current_section));
                        prev_section = current_section;
                    } else {
                        mListItems.add(current_item);
                    }
                    i++;
                }
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            if (!isCancelled()) {
                if (mListItems.size() <= 0) {
                    showEmptyText(mListView, mLoadingView, mEmptyView);
                } else {
                    setListAdaptor();
                    showContent(mListView, mLoadingView, mEmptyView);
                }
            }
            super.onPostExecute(result);
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        if (mListItems != null && mListItems.size() > 0) {
            outState.putStringArrayList("mListItems", mListItems);
        }
        if (mListSectionPos != null && mListSectionPos.size() > 0) {
            outState.putIntegerArrayList("mListSectionPos", mListSectionPos);
        }
        String searchText = mSearchView.getText().toString();
        if (searchText != null && searchText.length() > 0) {
            outState.putString("constraint", searchText);
        }
        super.onSaveInstanceState(outState);
    }

}

提前致谢......

这段代码被Mr. Bhavy mehta采纳在github上

这是我的日志猫

     FATAL EXCEPTION: AsyncTask #2
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:299)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
at java.util.concurrent.FutureTask.run(FutureTask.java:239)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
at java.lang.Thread.run(Thread.java:856)
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to 
at 

我也更新了我的日志猫

Answer 1

这里的问题在于performFiltering。

您已在该方法中将 filterItems 定义为

ArrayList<String> filterItems = new ArrayList<String>()

然后您将过滤项添加到过滤结果中，如下所示:

                result.count = filterItems.size();
                result.values = filterItems;

(其中结果是 FilterResults 类型)。

但是，稍后您将 filterResults 中的值强制转换为 publishResults 中的 List 类型:

List<Company> filtered = (List<Company>) results.values;

这会导致doInBackground中出现运行时异常，当运行时系统发现你传递给它的对象，声称是一个List 实际上是一个List

您的问题的解决方案是将 filterItems 更改为公司列表，而不是字符串，并在公司名称与 performFiltering 内循环中的 constraintStr 匹配时向其添加 mItems[i] 元素。

例如:

    protected FilterResults performFiltering(CharSequence constraint) {
        // NOTE: this function is *always* called from a background thread,
        // and
        // not the UI thread.
        String constraintStr = constraint.toString().toLowerCase();
        FilterResults result = new FilterResults();

        if (constraint != null && constraint.toString().length() > 0) {
            ArrayList<Company> filterItems = new ArrayList<Company>();

            synchronized (this) {
                for (int i = 0; i < mItems.size(); i++) {
                    Company company=mItems.get(i);
                    String companyName= company.companyName;
                    if (companyName.toLowerCase().startsWith(constraintStr)) {
                        filterItems.add(company);
                    }
                }
                result.count = filterItems.size();
                result.values = filterItems;
            }
        } else {
            synchronized (this) {
                result.count = mItems.size();
                result.values = mItems;
            }
        }
        return result;
    }