Question

我的currentDB中有一个变量MainActivity.java。我根据用户选择不同的选项卡将此变量启动到不同的值。相应的代码是：

@override
public void tab_selector(View v) {
    switch (v.getId()) {
        case R.id.veg_tab:
            setContentView(R.layout.vegetable);
            currentListView = (ListView) findViewById(R.id.veg_list);
            currentDB = "veg";
            break;
        case R.id.meat_tab :
            setContentView(R.layout.meat_drawer);
            currentListView = (ListView) findViewById(R.id.meat_list);
            currentDB = "meat";
            break;
        default:
            break;
    }

    currentList = mydb.getAllItems(currentDB);    // Definition below, works perfect
    itemAdder2.updateData(currentList);
    currentListView.setAdapter(itemAdder2);
}

我在DBHelper.java中有一个方法，理想情况下将表名和项id作为输入，并删除指定表中的相应行。

public Integer deleteItem (String dbName, int id)
{
    SQLiteDatabase db = this.getWritableDatabase();
    return db.delete(dbName,
            "id = ? ",
            new String[] { Integer.toString(id) });
}

这是从表中获取所有数据的另一个功能，它可以很好地工作。

public ArrayList<String> getAllItems(String dbName)
{
    ArrayList<String> array_list = new ArrayList<String>();

    //hp = new HashMap();
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor res =  db.rawQuery( "select * from " + dbName, null );
    res.moveToFirst();

    while(res.isAfterLast() == false){
        array_list.add(res.getString(res.getColumnIndex(COLUMN_NAME)));
        res.moveToNext();
    }
    return array_list;
}

我创建了一个自定义的ListViewAdapter，以显示存储在数据库中的数据。我已通过onClick()功能提供了相关按钮以进行编辑和删除。现在，我的问题是确定在ListViewAdapter内引用哪个数据库。我无法将currentDB信息从MainActivity.java传递给ListViewAdapter.java。请帮忙。提前致谢。 ListViewAdapter.java的代码段如下：

public class ListViewAdapter extends BaseAdapter {

Context mContext;
LayoutInflater mInflater;
ArrayList mArray;
DBHelper mydb;
String dbName;

public ListViewAdapter(Context context, LayoutInflater inflater) {
    mContext = context;
    mInflater = inflater;
    mArray = new ArrayList();
    mydb = new DBHelper(mContext);
    dbName = "veg";    // Didn't know what to do, tried to initialize manually, din't work :(
}

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

@Override
public Object getItem(int position) {
    return mArray.get(position);
}

@Override
public long getItemId(int position) {
    // your particular data set uses String IDs
    // but you have to put something in this method
    return position;
}

@Override
public View getView(final int position, View convertView, final ViewGroup parent) {
    ViewHolder holder;

    // check if the view already exists
    // if so, no need to inflate and findViewById again!
    if (convertView == null) {

        // Inflate the custom row layout from your XML.
        convertView = mInflater.inflate(R.layout.list_item, null);

        // create a new "Holder" with subviews
        holder = new ViewHolder();
        holder.itemNameView = (TextView) convertView.findViewById(R.id.item_name);
        holder.itemExpiryView = (TextView) convertView.findViewById(R.id.item_expiry);

        // Taking care of the buttons
        holder.editButton = (Button) convertView.findViewById(R.id.button_edit);
        holder.deleteButton = (Button) convertView.findViewById(R.id.button_delete);

        // hang onto this holder for future recycling
        convertView.setTag(holder);
    } else {

        // skip all the expensive inflation/findViewById
        // and just get the holder you already made
        holder = (ViewHolder) convertView.getTag();
    }

    // Set listener on the buttons
    holder.editButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Toast.makeText(mContext, "Edit Button CLicked", Toast.LENGTH_SHORT).show();
        }
    });

    holder.deleteButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            deleteItem(position);            // Potential problem here??
            Toast.makeText(mContext, "Item deleted", Toast.LENGTH_SHORT).show();
        }
    });

    // More code after this

    // Grab the title and author from the JSON
    String name = "";
    String expiry = "7 days";

    // Write appropriate codes to obtain values for the string variables above
    name = (String) getItem(position);

    // Send these Strings to the TextViews for display
    holder.itemNameView.setText(name);
    holder.itemExpiryView.setText(expiry);

    return convertView;
}

// this is used so you only ever have to do
// inflation and finding by ID once ever per View
private static class ViewHolder {
    public TextView itemNameView;
    public TextView itemExpiryView;
    public Button editButton;
    public Button deleteButton;
}

public void updateData(ArrayList arrayPassed) {
    // update the adapter's data set
    mArray = arrayPassed;
    notifyDataSetChanged();
}

public void deleteItem(int pos){
    mArray.remove(pos);            // Ideally, shouldn't be there
    mydb.deleteItem(dbName, pos);  // Here I need to pass the appropriate dbName
    // mArray = mydb.getAllItems(); // Ideally should be there
    notifyDataSetChanged();
}

}

如果您需要额外的东西，请告诉我。任何改述或主题，标签更改都是受欢迎的。作为一个菜鸟，没有能力如何传达。感谢您的帮助。：）

Answer 1

在适配器中创建一个公共方法来设置Db名称，例如：在ListViewAdapter类中，

public void setDbName(String dbName){
this.dbName = dbName;
}

在tab_selector（View v）方法中，将db Name设置为适配器

例如：

@override
public void tab_selector(View v) {
    switch (v.getId()) {
        case R.id.veg_tab:
            setContentView(R.layout.vegetable);
            currentListView = (ListView) findViewById(R.id.veg_list);
            currentDB = "veg";
            break;
        case R.id.meat_tab :
            setContentView(R.layout.meat_drawer);
            currentListView = (ListView) findViewById(R.id.meat_list);
            currentDB = "meat";
            break;
        default:
            break;
    }

    currentList = mydb.getAllItems(currentDB); 
    itemAdder2.updateData(currentList);
    currentListView.setAdapter(itemAdder2);
    itemAdder2.setDbName(currentDB );
}

Answer 2

这可能是不好的做法但是如何将currentDB变量设置为public和static，以便可以从其他类访问它！

Answer 3

我认为你可以在这里使用SharedPreferences

Answer 4

对我来说，这看起来就像是你试图将一个String变量从一个Activity发送到另一个类。此外，发送的字符串不是敏感信息。现在，这非常简单，可以使用LocalBroadCastManager完成。该用法已得到充分讨论 here .

Android中的变量传递？

4 个答案: