android：在 OnPrepareOptionsMenu 中需要帮助

Question

我有一个活动，在列表视图中包含来自 sqlitedatabase 的记录。 我的 OptionMenu 有一个“删除图标” 当列表视图中没有记录（列表视图为空）时，我想隐藏 optionMenu。 并在列表视图中有数据时显示 optionMenu。 我尝试了很多，搜索了那个。但找不到解决办法。

这是我的活动课

package com.munawwar.sultan.cursoradapter;

import android.app.ActionBar.LayoutParams;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import com.munawwar.sultan.R;
import com.munawwar.sultan.adapter.DBAdapter;

public class MeterAdapter extends Activity {
DBAdapter dbh;
SQLiteDatabase db;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.list_view_records);
    dbh = new DBAdapter(this);
    populateListview();
}

public void populateListview() {
    SimpleCursorAdapter mycursor;
    Cursor cursor;
    cursor = dbh.getAllMeter();
    startManagingCursor(cursor);
    String[] fromfields = new String[] { DBAdapter.COLUMN_METER_DATE,
            DBAdapter.COLUMN_METER_START, DBAdapter.COLUMN_METER_END };
    int[] tofields = new int[] { R.id.meterdate, R.id.meterstart,
            R.id.meterend };
    mycursor = new SimpleCursorAdapter(this, R.layout.row_meter, cursor,
            fromfields, tofields, 0);
    ListView mylist = (ListView) findViewById(R.id.list);

    // view if there is no record

    View empty = getLayoutInflater().inflate(R.layout.no_record_found,
            null, false);
    addContentView(empty, new LayoutParams(LayoutParams.MATCH_PARENT,
            LayoutParams.MATCH_PARENT));
    mylist.setEmptyView(empty);

    // mylist.setEmptyView(findViewById(android.R.id.empty));
    mylist.setAdapter(mycursor);
}

// ===============================================================================

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar actions click
    switch (item.getItemId()) {
    case R.id.action_delete:
        try {
            AlertDialog.Builder builder = new AlertDialog.Builder(this)
                    .setMessage(
                            "Are you sure you want to delete all Traveling data?")
                    .setNegativeButton(R.string.yes,
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,
                                        int which) {
                                    // *********
                                    db = dbh.getWritableDatabase();
                                    dbh.DeleteAllMeter();
                                    db.close();
                                    populateListview();

                                    dialog.dismiss();
                                }
                            })
                    .setPositiveButton(R.string.no,
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,
                                        int which) {
                                    dialog.dismiss();
                                }
                            });
            AlertDialog alert = builder.create();
            alert.show();
            return true;
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        // *******************
    default:
        return super.onOptionsItemSelected(item);
    }
}

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    return super.onPrepareOptionsMenu(menu);
}

}

Answer 1

将此语句移到populateListView() 方法之外，并使其成为类的成员变量：

SimpleCursorAdapter mycursor;

在onPrepareOptionsMenu() 中这样做：

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    int count = myCursor.getCount();
    if (count == 0) {
        return false; //Don't show options menu if list is empty
    }
    return true;
}