Question

当用户选择ListViewItem时，我正在更改该行的背景图像。这似乎发生得非常缓慢。我不确定为什么？

OnItemClickListener

listView.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> a, View v, int position, long id) {
                //quotesAdapter.setSelectedPosition(position);
                setupDetailView(position);
                setupChartView(position);
                setupARView(position);
                emptyView.setVisibility(View.INVISIBLE);

                ViewGroup vg = (ViewGroup)v;

                TextView nameText = (TextView) vg.findViewById(R.id.nameText);
                TextView priceText = (TextView) vg.findViewById(R.id.priceText);
                TextView changeText = (TextView) vg.findViewById(R.id.changeText);

                //change the old row back to normal
                if(oldView != null){
                    oldView.setBackgroundResource(R.drawable.stocks_gradient);
                    nameText.setTextAppearance(getApplicationContext(), R.style.BlueText);
                    priceText.setTextAppearance(getApplicationContext(), R.style.BlueText);
                    changeText.setTextAppearance(getApplicationContext(), R.style.BlueText);
                }

                //change the selected row
                v.setBackgroundResource(R.drawable.stocks_selected_gradient);
                nameText.setTextColor(Color.WHITE);
                priceText.setTextColor(Color.WHITE);
                changeText.setTextColor(Color.WHITE);

                //keep a reference to the old row, for the next time user clicks
                oldView = v;
            }
        });
    }

原始代码：

private class QuoteAdapter extends ArrayAdapter<Quote> {

        private ArrayList<Quote> items;
        // used to keep selected position in ListView
        private int selectedPos = -1; // init value for not-selected

        public QuoteAdapter(Context context, int textViewResourceId, ArrayList<Quote> items) {
            super(context, textViewResourceId, items);
            this.items = items;
        }

        public void setSelectedPosition(int pos) {
            selectedPos = pos;
            // inform the view of this change
            notifyDataSetChanged();
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View v = convertView;
            if (v == null) {
                LayoutInflater vi = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                v = vi.inflate(R.layout.mainrow, null);
            }

            TextView nameText = (TextView) v.findViewById(R.id.nameText);
            TextView priceText = (TextView) v.findViewById(R.id.priceText);
            TextView changeText = (TextView) v.findViewById(R.id.changeText);

            // change the row color based on selected state
            if (selectedPos == position) {
                v.setBackgroundResource(R.drawable.stocks_selected_gradient);
                nameText.setTextColor(Color.WHITE);
                priceText.setTextColor(Color.WHITE);
                changeText.setTextColor(Color.WHITE);
            } else {
                v.setBackgroundResource(R.drawable.stocks_gradient);
                nameText.setTextAppearance(getApplicationContext(), R.style.BlueText);
                priceText.setTextAppearance(getApplicationContext(), R.style.BlueText);
                changeText.setTextAppearance(getApplicationContext(), R.style.BlueText);
            }

            Quote q = items.get(position);
            if (q != null) {
                if (nameText != null) {
                    nameText.setText(q.getSymbol());
                }
                if (priceText != null) {
                    priceText.setText(q.getLastTradePriceOnly());
                }
                if (changeText != null) {
                    try {
                        float floatedChange = Float.valueOf(q.getChange());
                        if (floatedChange < 0) {
                            if (selectedPos != position)
                                changeText.setTextAppearance(getApplicationContext(), R.style.RedText); // red
                        } else {
                            if (selectedPos != position)
                                changeText.setTextAppearance(getApplicationContext(), R.style.GreenText); // green
                        }
                    } catch (NumberFormatException e) {
                        System.out.println("not a number");
                    } catch (NullPointerException e) {
                        System.out.println("null number");
                    }
                    changeText.setText(q.getChange() + " (" + q.getPercentChange() + ")");
                }
            }
            return v;
        }
    }

更新：具有ViewHolder模式的适配器

   private class QuoteAdapter extends ArrayAdapter<Quote> {

        private ArrayList<Quote> items;
        // used to keep selected position in ListView
        private int selectedPos = -1; // init value for not-selected

        public QuoteAdapter(Context context, int textViewResourceId, ArrayList<Quote> items) {
            super(context, textViewResourceId, items);
            this.items = items;
        }

        public void setSelectedPosition(int pos) {
            selectedPos = pos;
            // inform the view of this change
            notifyDataSetChanged();
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View v = convertView;
            ViewHolder holder; // to reference the child views for later actions

            if (v == null) {
                LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                v = vi.inflate(R.layout.mainrow, null);

                // cache view fields into the holder
                holder = new ViewHolder();
                holder.nameText = (TextView) v.findViewById(R.id.nameText);
                holder.priceText = (TextView) v.findViewById(R.id.priceText);
                holder.changeText = (TextView) v.findViewById(R.id.changeText);

                // associate the holder with the view for later lookup
                v.setTag(holder);
            }
            else {
                // view already exists, get the holder instance from the view
                holder = (ViewHolder)v.getTag();
            }

            // change the row color based on selected state
            if (selectedPos == position) {
                v.setBackgroundResource(R.drawable.stocks_selected_gradient);
                holder.nameText.setTextColor(Color.WHITE);
                holder.priceText.setTextColor(Color.WHITE);
                holder.changeText.setTextColor(Color.WHITE);
            } else {
                v.setBackgroundResource(R.drawable.stocks_gradient);
                holder.nameText.setTextAppearance(getApplicationContext(), R.style.BlueText);
                holder.priceText.setTextAppearance(getApplicationContext(), R.style.BlueText);
                holder.changeText.setTextAppearance(getApplicationContext(), R.style.BlueText);
            }

            Quote q = items.get(position);
            if (q != null) {
                if (holder.nameText != null) {
                    holder.nameText.setText(q.getSymbol());
                }
                if (holder.priceText != null) {
                    holder.priceText.setText(q.getLastTradePriceOnly());
                }
                if (holder.changeText != null) {
                    try {
                        float floatedChange = Float.valueOf(q.getChange());
                        if (floatedChange < 0) {
                            if (selectedPos != position)
                                holder.changeText.setTextAppearance(getApplicationContext(), R.style.RedText); // red
                        } else {
                            if (selectedPos != position)
                                holder.changeText.setTextAppearance(getApplicationContext(), R.style.GreenText); // green
                        }
                    } catch (NumberFormatException e) {
                        System.out.println("not a number");
                    } catch (NullPointerException e) {
                        System.out.println("null number");
                    }
                    holder.changeText.setText(q.getChange() + " (" + q.getPercentChange() + ")");
                }
            }
            return v;
        }
    }

Answer 1

您的getView()是o.k. （即使它可以更快）。我认为问题出在setSelectedPosition()。您正在调用notifyDataSetChanged（），这会导致重新绘制太多视图。您应该使用有状态的drawable来处理选择背景。

Answer 2

我会承认我不知道您的数据集有多大，也不知道一次有多少可见元素在屏幕上，但是如果您可以保证您的列表处于单一选择模式并且具有状态可绘制的具有不同颜色的正确状态

<selector xmlns:android="http://schemas.android.com/apk/res/android"
    android:dither="true" >
    <item
        android:state_pressed="true"
        android:state_enabled="true"
        android:drawable="@color/my_color" />

    <item
        android:state_selected="true"
        android:drawable="@color/my_color" />
    </item>

    <item
        android:state_focused="true"
        android:state_enabled="true"
        android:drawable="@android:drawable/list_selector_background" />
</selector>

这应该会自动生效。

如果您希望所选状态看起来像是粘滞的，您也可以尝试进行listView多重选择，并拦截调用以设置选择以取消先前的选择。

如果您仍打算手动设置背景，我会使用其他人使用的getView模式优化您的ViewHolder方法。这将使您的重绘更便宜并且看起来好像实际上没有发生（同样取决于当时屏幕上的元素数量）

http://developer.android.com/resources/samples/ApiDemos/src/com/example/android/apis/view/List14.html

ArrayAdapter的getView（）速度很慢

2 个答案: