从 onOptionsItemSelected 访问列表视图

Posted 2023-05-07

【中文标题】从 onOptionsItemSelected 访问列表视图

【英文标题】：Accessing the listview from onOptionsItemSelected

【发布时间】：2015-07-05 10:50:07

【问题描述】：

在购物车活动中，我有一个listview，并在其上放置了一个imagebutton，如class_list_group.xml 所示。当活动开始时，我想隐藏imagebutton。但是一旦按下操作栏中的编辑按钮（活动类中的onOptionsItemSelected），我想显示一个带有imagebutton 的相对布局，如xml文件所示。

这是我的问题，我的问题是我该怎么做？任何帮助将不胜感激。它与我所说的空点异常有关。

Shoppingcartactivity.java 类

    public class ShoppingCartActivity extends Activity 

    private TextView totalTV;
    private TextView discountTV;
    private TextView totalExclTV;
    private TextView totalTaxTV;
    private TextView netPriceTV;
    private ProductAdapter mProductAdapter;
    private ExpandableListView expListView;
    private EditText couponET;
    private ImageButton couponBTN;
    private List<Product> mCartList;
    List<String> listDataHeader;
    HashMap<String, List<String>> listDataChild;
    private String Strdiscount;
    private double discount;
    public JSONObject DiscountObj;
    private double addSubTotal;
    RelativeLayout hiddenEditDelete;

    @Override
    public void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.cart_activity);

        ActionBar actionBar = getActionBar();
        getActionBar().setIcon(
                new ColorDrawable(getResources().getColor(
                        android.R.color.transparent)));
        getWindow().setSoftInputMode(
                WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN);
        // Enabling Back navigation on Action Bar icon
        actionBar.setDisplayHomeAsUpEnabled(true);

        mCartList = ShoppingCartHelper.getCartList();

        expListView = (ExpandableListView) findViewById(R.id.lvExp);
        mProductAdapter = new ProductAdapter(this, mCartList,
                getLayoutInflater(), true);

        // setting list adapter
        expListView.setAdapter(mProductAdapter);

        totalTV = (TextView) findViewById(R.id.total_valueamount);
        discountTV = (TextView) findViewById(R.id.discount_valueamount);
        totalExclTV = (TextView) findViewById(R.id.exl_tax_valueamount);
        totalTaxTV = (TextView) findViewById(R.id.ttl_tax_valueamount);
        netPriceTV = (TextView) findViewById(R.id.net_price_valueamount);
        couponBTN = (ImageButton) findViewById(R.id.btncoupon);
        couponET = (EditText) findViewById(R.id.ET_coupon);
        hiddenEditDelete = (RelativeLayout) findViewById(R.id.rl_cartedit);
        hiddenEditDelete.setVisibility(View.GONE);
        couponET.setEnabled(false);
        couponBTN.setEnabled(false);
        priceCalculation();

        double taxamount = (addSubTotal * 5) / 100;
        double netTotal = addSubTotal + taxamount;

        DecimalFormat df = new DecimalFormat("#.##");

        addSubTotal = Double.valueOf(df.format(addSubTotal));
        taxamount = Double.valueOf(df.format(taxamount));
        netTotal = Double.valueOf(df.format(netTotal));

        totalTV.setText(Double.toString(addSubTotal));
        discountTV.setText("0.0");
        totalExclTV.setText(Double.toString(addSubTotal));
        totalTaxTV.setText(Double.toString(taxamount));
        netPriceTV.setText(Double.toString(netTotal));



//      couponBTN.setOnClickListener(new View.OnClickListener() 
//          public void onClick(View v) 
//
//              try 
//                  String CouponCode = couponET.getText().toString();
//
//                  if (!Utility.isNotNull(CouponCode)) 
//                      Toast.makeText(getApplicationContext(),
//                              "Insert coupon code", Toast.LENGTH_LONG).show();
//                   else 
//                      new CouponAsyncTask(ShoppingCartActivity.this)
//                              .execute(CouponCode);
//                  
//               catch (Exception e) 
//                  e.printStackTrace();
//              
//          
//      );

    

    public void loadCouponData() 

        Strdiscount = DiscountObj.optString("Discount");
        try 
            Log.i("Discount", DiscountObj.getString("Discount"));
         catch (JSONException e) 
            e.printStackTrace();
        

    

    public void priceCalculation() 

        for (int i = 0; i < mCartList.size(); i++) 

            if (!mCartList.isEmpty()) 
                couponET.setEnabled(true);
                couponBTN.setEnabled(true);
            
            Product cat = mCartList.get(i);
            addSubTotal += cat.subTotal;
        
    


    @Override
    public boolean onCreateOptionsMenu(Menu menu) 
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.main_cart, menu);

        return super.onCreateOptionsMenu(menu);
    

    @Override
    public boolean onOptionsItemSelected(MenuItem item) 
        // Take appropriate action for each action item click
        switch (item.getItemId()) 
        case android.R.id.home:
            onBackPressed();
            finish();
            overridePendingTransition(R.anim.slide_in_left,
                    R.anim.slide_out_right);
            return true;
        case R.id.action_edit:
            hiddenEditDelete.setVisibility(View.VISIBLE);
            overridePendingTransition(R.anim.slide_in_right,
                    R.anim.slide_out_left);
            return true;

        default:
            return super.onOptionsItemSelected(item);
        
    

class_list_group.xml 类

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_
    android:layout_
    android:orientation="vertical" >

    <LinearLayout
        android:id="@+id/shareLILayout1"
        android:layout_
        android:layout_
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:orientation="horizontal"
        android:paddingTop="3dp"
        android:weightSum="5" >

        <TextView
            android:id="@+id/lblListHeader"
            android:layout_
            android:layout_
            android:layout_alignParentTop="true"
            android:layout_weight="3"
            android:paddingBottom="4dp"
            android:paddingLeft="28dp"
            android:paddingTop="4dp"
            android:singleLine="true"
            android:textColor="#000000"
            android:textSize="13sp"
            android:textStyle="bold" />

    </LinearLayout>

    <RelativeLayout
        android:id="@+id/rl_cartedit"
        android:layout_
        android:layout_
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:gravity="center"
        android:orientation="horizontal"
        android:paddingBottom="4dp" >

        <ImageButton
            android:id="@+id/btneditcartitem"
            android:layout_
            android:layout_
            android:layout_marginRight="8dp"
            android:layout_marginTop="8dp"
            android:background="#ffffff"
            android:src="@drawable/edititem" />

    </RelativeLayout>

</RelativeLayout>

ProductAdapter .java

public class ProductAdapter extends BaseExpandableListAdapter 

    private List<Product> mCartList;
    private Context _context;
    private List<Product> _cartList;
    private boolean mShowQuantity;

    public ProductAdapter(Context context, List<Product> cartList,
            LayoutInflater inflater, boolean showQuantity) 
        this._context = context;
        this._cartList = cartList;
        mShowQuantity = showQuantity;
    

    @Override
    public Object getChild(int groupPosition, int childPosition) 
        return _cartList.get(groupPosition).getItems().get(childPosition);
    

    @Override
    public long getChildId(int groupPosition, int childPosition) 
        return _cartList.get(groupPosition).getItems().get(childPosition)
                .hashCode();
    

    @Override
    public View getChildView(int groupPosition, int childPosition,
            boolean isLastChild, View convertView, ViewGroup parent) 

        View v = convertView;

        if (v == null) 
            LayoutInflater inflater = (LayoutInflater) _context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = inflater.inflate(R.layout.cart_list_item, parent, false);
        

        TextView itemSize = (TextView) v.findViewById(R.id.lblListItemSize);

        Item det = _cartList.get(groupPosition).getItems().get(childPosition);

        itemSize.setText(det.itemName + " ( " + det.price + " ) ");

        mCartList = ShoppingCartHelper.getCartList();

        return v;
    

    @Override
    public int getChildrenCount(int groupPosition) 
        int size = _cartList.get(groupPosition).getItems().size();
        System.out.println("Child for group [" + groupPosition + "] is ["
                + size + "]");
        return size;
    

    @Override
    public Object getGroup(int groupPosition) 
        return this._cartList.get(groupPosition);
    

    @Override
    public int getGroupCount() 
        return this._cartList.size();
    

    @Override
    public long getGroupId(int groupPosition) 
        return groupPosition;
    

    @Override
    public View getGroupView(final int groupPosition, boolean isExpanded,
            View convertView, ViewGroup parent) 

        View v = convertView;

        if (v == null) 
            LayoutInflater inflater = (LayoutInflater) _context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = inflater.inflate(R.layout.cart_list_group, parent, false);
        

        TextView groupName = (TextView) v.findViewById(R.id.lblListHeader);
        TextView groupQty = (TextView) v.findViewById(R.id.lbl_qty);
        TextView groupSubtotal = (TextView) v.findViewById(R.id.lblsubtotal);

        final Product cat = _cartList.get(groupPosition);

//      ShoppingCartEntry catalog = ShoppingCartHelper.getByProduct(cat);
//      int productIndex = getIntent().getExtras().getInt(
//              ShoppingCartHelper.PRODUCT_INDEX);
//      final Product selectedProduct = catalog.get(productIndex);


        groupName.setText(cat.description);
        groupQty.setText(String.valueOf(cat.quantity));
        groupSubtotal.setText(Double.toString(cat.subTotal));

        ImageButton editIB = (ImageButton) v.findViewById(R.id.btneditcartitem);

        if (cat.itemCategory != null && cat.itemCategory.equals("Pizza"))
            editIB.setOnClickListener(new View.OnClickListener() 
            @Override
            public void onClick(View view) 

                Intent next = new Intent(_context, ActivityEdit.class);
                Bundle b = new Bundle();
                b.putDouble("subTotal", cat.subTotal);
                next.putExtras(b);
                next.putExtra("description", cat.description);

                _context.startActivity(next);
                ((Activity) _context).overridePendingTransition(
                        R.anim.slide_in_right, R.anim.slide_out_left);
            
        );


        return v;
    

    @Override
    public boolean hasStableIds() 
        return true;
    

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) 
        return true;
    

cart_Activity

 <ExpandableListView
    android:id="@+id/lvExp"
    android:layout_
    android:layout_
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/grid_topics"
    android:cacheColorHint="#00000000"
    android:groupIndicator="@drawable/group_indicator" >
</ExpandableListView>

【问题讨论】：

你为什么不用.setVisibility(View.)？

我在我的活动中使用了这个 hiddenEditDelete.setVisibility(View.GONE);。但导致崩溃

显示崩溃报告。

这是第 79 行，它崩溃了。 hiddenEditDelete.setVisibility(View.GONE);

hiddenEditDelete 是您在 class_list_group.xml 中，而不是在 cart_activity 中。这会导致空指针异常。

【参考方案1】：

在 onCreate 方法中使用之前，您还没有初始化 hiddenEditDelete，这就是抛出 NPE 的原因。另外，我认为应该最后调用setContentView

    @Override
    public void onCreate(Bundle savedInstanceState) 
      super.onCreate(savedInstanceState);

      expListView = (ExpandableListView) findViewById(R.id.lvExp);
      mProductAdapter = new ProductAdapter(this, mCartList,
            getLayoutInflater(), true);

      expListView.setAdapter(mProductAdapter);

      hiddenEditDelete = (RelativeLayout) findViewById(R.id.rl_cartedit);
      hiddenEditDelete.setVisibility(View.GONE);

      setContentView(R.layout.cart_activity);
   

【讨论】：

在方法结束时调用setContenView

还是一样的结果。兄弟可以从主要活动中访问列表视图项目吗？我认为问题在于。在不使用 hiddenEditDelete 行的情况下运行应用程序时，它可以工作。

您会在问题中添加cart_activity xml 代码吗？

我只有一个列表查看这个id，lvExp

如果我们看不到代码很难帮助你，我也注意到expListView，mProductAdapter 和mCartList没有在你的活动中声明，所以我是想知道这段代码是如何构建的，而且即使它可以构建，mCartList 应该是 null 因此你的适配器会抛出 NPE

【参考方案2】：

问题是您在访问 hiddenEditDelete（如 expListView）之前没有对它进行任何引用，您必须在使用之前使用正确的布局 ID 对其进行实例化。然后你可以对布局做任何你想做的事情。 onCreate() 中的其他一切都是正确的

@Override
public void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.cart_activity);

    expListView = (ExpandableListView) findViewById(R.id.lvExp);
mProductAdapter = new ProductAdapter(this, mCartList,
        getLayoutInflater(), true);

expListView.setAdapter(mProductAdapter);

    hiddenEditDelete.setVisibility(View.GONE);

【讨论】：

好的，我明白了。那么你能告诉我应该在 onCreate() 中添加什么吗？

在访问布局之前在 create 中写入 hiddenEditDelete=(RelativeLayout)findViewById(YOUR_XML_ID);

我有这一行 hiddenEditDelete = (RelativeLayout) findViewById(R.id.rl_cartedit);

那么它应该可以工作。您能否提供错误的堆栈跟踪？

您能否检查一下 rl_cartedit 在您的 cart_activity xml 中是否可用？