当用户选择ListViewItem时，我正在更改该行的背景图像。这似乎发生得很慢。我不确定为什么吗？
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;
}
}
最佳答案
您的getView()是。 （即使可以使其更快）。我认为问题出在setSelectedPosition()上。您正在调用notifyDataSetChanged（），这将导致太多视图被重新绘制。您应该使用有状态可绘制对象来处理选择背景。