Adapter两种适配及其他

——这个不难，记住很简单

1.Adapter的两种适配

ONE item view type

MULTIPLE item view types

所以对于显示天气，今天和未来天气的item可以同时适配的。

这个是CursorAdapter中的一个函数

/**
* @see android.widget.ListAdapter#getView(int, View, ViewGroup)
*/
public View getView(int position, View convertView, ViewGroup parent) {
if (!mDataValid) {
throw new IllegalStateException("this should only be called when the cursor is valid");
}
if (!mCursor.moveToPosition(position)) {
throw new IllegalStateException("couldn't move cursor to position " + position);
}
View v;
if (convertView == null) {
v = newView(mContext, mCursor, parent);
} else {
v = convertView;
}
bindView(v, mContext, mCursor);
return v;
}

看到其中的newView和bindView就是继承CursorAdapter的类需要自己实现的。

回到主题上，在MULTIPLE中，today和future_day是两种view。这就需要override CursorAdapter中两个关于view type的函数：

public int getItemViewType(int position);
public int getViewTypeCount();

第一个是根据cursor中记录的位置返回view type，（返回值从0，1，2，……）在天气中就是，位置在0的记录为今天的天气，需要返回VIEW_TYPE_TODAY；其他位置则为未来天气的记录，返回VIEW_TYPE_FUTURE_DAY。

第二个是返回view type的数目，还是说天气这个，显然是两种，则返回2；view type的范围自然就是0和1了。

下面是Forecast部分：（忽略bindView部分，填充View的部分）

public class ForecastAdapter extends CursorAdapter{

private final int VIEW_TYPE_TODAY = 0;
private final int VIEW_TYPE_FUTURE_DAY = 1;
private final int VIEW_TYPE_COUNT = 2;

public ForecastAdapter(Context context, Cursor c, int flags) {
super(context, c, flags);
}

@Override
public int getItemViewType(int position){

return (position == 0) ? VIEW_TYPE_TODAY : VIEW_TYPE_FUTURE_DAY;
}

@Override
public int getViewTypeCount(){
return VIEW_TYPE_COUNT;
}

@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {

//View view = LayoutInflater.from(context).inflate(R.layout.list_item_forecast,parent,false);

//Choose the layout type
int viewType = getItemViewType(cursor.getPosition());
int layoutId = -1;

//TODO: Determine layoutId from viewType
switch (viewType){
case VIEW_TYPE_TODAY:
layoutId = R.layout.list_item_forecast_today;
break;
case VIEW_TYPE_FUTURE_DAY:
layoutId = R.layout.list_item_forecast;
break;
}

return LayoutInflater.from(context).inflate(layoutId,parent , false);
}

@Override
public void bindView(View view, Context context, Cursor cursor) {
//Read weather icon ID from cursor
//Use placeholder image for now
//TODO Read date from cursor
//TODO Read weather forecast from cursor
//Read user preference for metric or imperial temperature units
//Read high temperature from cursor
//TODO Read low temperature from cursor

}
}

2. 使用ViewHolder（bindView）

这是bindView中的内容，读取出记录，然后填充相应的view，显示。

/*
This is where we fill-in the views with the contents of the cursor.
*/
@Override
public void bindView(View view, Context context, Cursor cursor) {
// our view is pretty simple here --- just a text view
// we'll keep the UI functional with a simple (and slow!) binding.

// Read weather icon ID from cursor
int weatherId = cursor.getInt(ForecastFragment.COL_WEATHER_ID);
// Use placeholder image for now
ImageView iconView = (ImageView) view.findViewById(R.id.list_item_icon);
iconView.setImageResource(R.drawable.ic_launcher);

// Read date from cursor
long dateInMillis = cursor.getLong(ForecastFragment.COL_WEATHER_DATE);
// Find TextView and set formatted date on it
TextView dateView = (TextView) view.findViewById(R.id.list_item_date_textview);
dateView.setText(Utility.getFriendlyDayString(context, dateInMillis));

// Read weather forecast from cursor
String description = cursor.getString(ForecastFragment.COL_WEATHER_DESC);
// Find TextView and set weather forecast on it
TextView descriptionView = (TextView) view.findViewById(R.id.list_item_forecast_textview);
descriptionView.setText(description);

// Read user preference for metric or imperial temperature units
boolean isMetric = Utility.isMetric(context);

// Read high temperature from cursor
double high = cursor.getDouble(ForecastFragment.COL_WEATHER_MAX_TEMP);
TextView highView = (TextView) view.findViewById(R.id.list_item_high_textview);
highView.setText(Utility.formatTemperature(high, isMetric));

// Read low temperature from cursor
double low = cursor.getDouble(ForecastFragment.COL_WEATHER_MIN_TEMP);
TextView lowView = (TextView) view.findViewById(R.id.list_item_low_textview);
lowView.setText(Utility.formatTemperature(low, isMetric));
}

这里面的图片、日期、高温、低温、预报等item看起来很杂乱，我们可以使用ViewHolder让它看起来清爽一些：

在ForecastAdapter中加入static class ViewHolder

public static class ViewHolder{

private final ImageView iconView;
private final TextView dateView;
private final TextView forecastView;
private final TextView highView;
private final TextView lowView;

public ViewHolder(View view) {

iconView = (ImageView)view.findViewById(R.id.list_item_icon);
dateView = (TextView)view.findViewById(R.id.list_item_date_textview);
forecastView = (TextView)view.findViewById(R.id.list_item_forecast_textview);
highView = (TextView)view.findViewById(R.id.list_item_high_textview);
lowView = (TextView)view.findViewById(R.id.list_item_low_textview);
}

修改newView：

......

View view = LayoutInflater.from(context).inflate(layoutId,parent , false);
ViewHolder viewHolder = new ViewHolder(view);
view.setTag(viewHolder);

return view;

newView则如下所示：（也是有点杂乱的，不过好一些了）

@Override
public void bindView(View view, Context context, Cursor cursor) {

ViewHolder viewHolder = (ViewHolder)view.getTag();
viewHolder.iconView.setImageResource(R.drawable.ic_launcher);

long dateMillis = cursor.getLong(ForecastFragment.COL_WEATHER_DATE);
viewHolder.dateView.setText(Utility.getFriendlyDayString(context,dateMillis));

String description = cursor.getString(ForecastFragment.COL_WEATHER_DESC);
viewHolder.descriptionView.setText(description);

//Read user preference for metric or imperial temperature units
boolean isMetric = Utility.isMetric(context);

//Read high temperature from cursor
double high = cursor.getDouble(ForecastFragment.COL_WEATHER_MAX_TEMP);
viewHolder.highView.setText(Utility.formatTemperature(context,high,isMetric));

double low = cursor.getDouble(ForecastFragment.COL_WEATHER_MIN_TEMP);
viewHolder.lowView.setText(Utility.formatTemperature(context, low , isMetric));
}

String转换为Double：

Double.valueOf(testString);