变量传入 Android？

Question

我的 MainActivity.java 中有一个变量 currentDB。根据用户选择不同的选项卡，我将此变量初始化为不同的值。对应的代码是：

@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，理想情况下采用 table 名称和项目 ID 作为输入，并从指定的 table.

中删除相应的行

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

这是从 table 获取所有数据的又一个函数，它工作得很好。

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。我通过 onClick() 功能提供了用于编辑和删除的相关按钮。现在，我的问题是确定在 ListViewAdapter 中引用哪个数据库。我无法将 currentDB 信息从 MainActivity.java 传递到 ListViewAdapter.java。请帮忙。提前致谢。 ListViewAdapter.java 的代码片段如下：

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。欢迎任何改写或主题，标签更改。作为菜鸟，无法准确表达。感谢你的帮助。 :)

Answer 1

这可能是不好的做法，但是如何设置 currentDB 变量 public 和静态，这样您就可以从另一个 class!

访问它

Answer 2

我想你可以在这里使用 SharedPreferences

Answer 3

对我来说，这看起来就像您只是想将一个字符串变量从一个 Activity 发送到另一个 class。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。使用已被很好地讨论 here .

Answer 4

在适配器中创建一个public方法来设置Db名称，例如：在 ListViewAdapter class,

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

然后在 tab_selector(View v) 方法中将数据库名称设置为适配器

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 );
}

变量传入 Android？

Variable Passing in Android?

android

sqliteopenhelper

listview-adapter