Question

我在我的Fragment java类中使用sqlite中的自动完整文本侦听器，不幸的是我有一个错误nullpointerexception。这是我的logcat：

05-12 09:15:05.987: E/AndroidRuntime(20901): FATAL EXCEPTION: main
05-12 09:15:05.987: E/AndroidRuntime(20901): Process: iot.bayadcenter.slidingmenu, PID: 20901
05-12 09:15:05.987: E/AndroidRuntime(20901): java.lang.NullPointerException
05-12 09:15:05.987: E/AndroidRuntime(20901):    at iot.bayadcenter.slidingmenu.billers.Payment.getItemsFromDb(Payment.java:271)
05-12 09:15:05.987: E/AndroidRuntime(20901):    at iot.bayadcenter.searchbarsqlite.CustomAutoCompleteTextChangedListener.onTextChanged(CustomAutoCompleteTextChangedListener.java:42)
05-12 09:15:05.987: E/AndroidRuntime(20901):    at android.widget.TextView.sendOnTextChanged(TextView.java:7610)
05-12 09:15:05.987: E/AndroidRuntime(20901):    at android.widget.TextView.handleTextChanged(TextView.java:7672)

这是我的CustomAutoCompleteTextChangedListener.java

public class CustomAutoCompleteTextChangedListener implements TextWatcher{

public static final String TAG = "CustomAutoCompleteTextChangedListener.java";
Context context;

public CustomAutoCompleteTextChangedListener(Context context){
    this.context = context;
}


@Override
public void onTextChanged(CharSequence userInput, int start, int before, int count) {

    // if you want to see in the logcat what the user types
    Log.e(TAG, "User input: " + userInput);

    Payment mainActivity = new Payment();

    // query the database based on the user input
    mainActivity.item = mainActivity.getItemsFromDb(userInput.toString());//HERE IS LINE 42

    // update the adapater
    mainActivity.myAdapter.notifyDataSetChanged();
    mainActivity.myAdapter = new ArrayAdapter<String>(mainActivity.getActivity(), android.R.layout.simple_dropdown_item_1line, mainActivity.item);
    mainActivity.myAutoComplete.setAdapter(mainActivity.myAdapter);

}

}

这是我的片段（Payment.java）

public class Payment extends Fragment {

CustomAutoCompleteView myAutoComplete;

    // adapter for auto-complete
    ArrayAdapter<String> myAdapter;

    // for database operations
    DatabaseHandler databaseH;

    // just to add some initial value
    String[] item = new String[] {"Please search..."};

    Context ctx = getActivity();

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

            myAutoComplete = (CustomAutoCompleteView) rootView.findViewById(R.id.myautocomplete);

            // add the listener so it will tries to suggest while the user types
            myAutoComplete.addTextChangedListener(new CustomAutoCompleteTextChangedListener(getActivity()));

            // set our adapter
            myAdapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_dropdown_item_1line, item);
            myAutoComplete.setAdapter(myAdapter);

这是另一部分：

// this function is used in CustomAutoCompleteTextChangedListener.java
    public String[] getItemsFromDb(String searchTerm){

        // add items on the array dynamically
        List<MyObject> products = databaseH.read(searchTerm);//HERE IS MY LINE 27
        int rowCount = products.size();

        String[] item = new String[rowCount];
        int x = 0;

        for (MyObject record : products) {

            item[x] = record.objectName;
            x++;
        }

        return item;
    }

Answer 1

由于这里有一大堆例外，让我们从第一个可见的开始。第271行产生NullPointerException，这是

List<MyObject> products = databaseH.read(searchTerm);

我想这是因为databaseH为空。检查是否正确打开连接。这一行也让我想知道Payment mainActivity = new Payment();。在自定义类中创建Fragment的新实例，该实例实现TextWatcher ...不要调用Fragment中的任何方法，除非它不在屏幕上。此外，Fragment用于附加到Activity，但不用于处理数据库方法。看一下模式MVC。我认为修复错误没有太大意义，最好重组一切。希望它至少有一点帮助。

片段 - 无法从'CustomAutoCompleteTextChangedListener'中的上下文强制转换

1 个答案: