这是我的ArrayAdapter。我希望通过遵循ViewHolder模式来提高效率:
但我不确定如何做到这一点。
更新:ViewHolder模式
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;
}
}
答案 0 :(得分:49)
ViewHolder基本上是一个静态类实例,它在创建时与视图关联,缓存您在运行时查找的子视图。如果视图已存在,请检索持有者实例并使用其字段而不是调用findViewById
。
在你的情况下:
@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();
}
// no local variables with findViewById here
// use holder.nameText where you were
// using the local variable nameText before
return v;
}
// somewhere else in your class definition
static class ViewHolder {
TextView nameText;
TextView priceText;
TextView changeText;
}
告诫:我没有尝试编译这个,所以请耐心等待。
答案 1 :(得分:0)
我在这里遇到了类似的问题,但是稍微复杂一点,请考虑一个非常相似的示例。
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;
ViewHolder holder;
if (v == null) {
LayoutInflater vi =
(LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = vi.inflate(R.layout.mainrow, null);
holder = new ViewHolder();
holder.nameText = (TextView) v.findViewById(R.id.nameText);
holder.priceText = (TextView) v.findViewById(R.id.priceText);
holder.myCheckbox = (Checkbox) v.findViewById(R.id.changeText);
v.setTag(holder);
}
else {
holder = (ViewHolder) v.getTag();
/*ATTENTION - this line below was added, because i started to face some problems with view reuse of other rows, when user changed the state, the behavior of other row was triggered*/
holder.myCheckbox.setOnCheckedChangeListener(null);
}
/*without the new line above, the line below trigger the old event and some strange behavior happens.*/
holder.myCheckbox.setChecked(myList.get(position).isChecked());
holder.myCheckbox.setOnCheckedChangeListener(()->{
//some behavior
});
return v;
}
// somewhere else in your class definition
static class ViewHolder {
TextView nameText;
TextView priceText;
Checkbox myCheckbox;
}
因此,请记住,使用ViewHolder模式时,最好在更改组件侦听器的状态之前对其进行清理。