昨天看了一下ArrayAdapter的源代碼,發現它還真把BaseAdapter封裝的不錯。故今天從源碼的角度來看看ArrayAdapter。java
搞android都知道ArrayAdapter的基本用法,就是在初始化ArrayAdapter的時候,無論你調用那一個構造類,都會調用這個方法:android
private void init(Context context, int resource, int textViewResourceId, List<T> objects) { mContext = context; mInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); mResource = mDropDownResource = resource; mObjects = objects; mFieldId = textViewResourceId; }
而後當你的ListView調用setAdapter的時候,ArrayAdapter就回調用這個方法:
網絡
/** * {@inheritDoc} */ public View getView(int position, View convertView, ViewGroup parent) { return createViewFromResource(position, convertView, parent, mResource); } private View createViewFromResource(int position, View convertView, ViewGroup parent, int resource) { View view; TextView text; if (convertView == null) { view = mInflater.inflate(resource, parent, false); } else { view = convertView; } try { if (mFieldId == 0) { // If no custom field is assigned, assume the whole resource is a TextView text = (TextView) view; } else { // Otherwise, find the TextView field within the layout text = (TextView) view.findViewById(mFieldId); } } catch (ClassCastException e) { Log.e("ArrayAdapter", "You must supply a resource ID for a TextView"); throw new IllegalStateException( "ArrayAdapter requires the resource ID to be a TextView", e); } T item = getItem(position); if (item instanceof CharSequence) { text.setText((CharSequence)item); } else { text.setText(item.toString()); } return view; }
但咱們發現沒有,咱們ArrayAdapter是一個實體類,而咱們在實際工做中大部分用到的的BaseAdapter是一個抽象類,因此咱們必須須要重寫BaseAdapter中的四個抽象方法,但在ArrayAdapter中咱們就不須要了,看代碼:ide
/** * {@inheritDoc} */ public int getCount() { return mObjects.size(); } /** * {@inheritDoc} */ public T getItem(int position) { return mObjects.get(position); } /** * {@inheritDoc} */ public long getItemId(int position) { return position; } /** * {@inheritDoc} */ public View getView(int position, View convertView, ViewGroup parent) { return createViewFromResource(position, convertView, parent, mResource); }
在ArrayAdapter中已經把這四個抽象方法給實現了,那從此咱們在設置setAdapter的時候,讓咱們的自定義Adapter直接繼承ArrayAdapter,而後重寫getView豈不是更好,而後咱們就和那三個基本沒有意義的三個抽象方法說拜拜了。佈局
而後咱們在看ArrayAdapter,發現它還實現了Filterable這個接口,而後重寫了:ui
/** * {@inheritDoc} */ public Filter getFilter() { if (mFilter == null) { mFilter = new ArrayFilter(); } return mFilter; }
這個方法,有的人會問這個方法有什麼用啊,那就得說說Filter這個抽象類了,在ArrayAdapter中有一個成員內部類:spa
/** * <p>An array filter constrains the content of the array adapter with * a prefix. Each item that does not start with the supplied prefix * is removed from the list.</p> */ private class ArrayFilter extends Filter { @Override protected FilterResults performFiltering(CharSequence prefix) { FilterResults results = new FilterResults(); if (mOriginalValues == null) { synchronized (mLock) { mOriginalValues = new ArrayList<T>(mObjects); } } if (prefix == null || prefix.length() == 0) { ArrayList<T> list; synchronized (mLock) { list = new ArrayList<T>(mOriginalValues); } results.values = list; results.count = list.size(); } else { String prefixString = prefix.toString().toLowerCase(); ArrayList<T> values; synchronized (mLock) { values = new ArrayList<T>(mOriginalValues); } final int count = values.size(); final ArrayList<T> newValues = new ArrayList<T>(); for (int i = 0; i < count; i++) { final T value = values.get(i); final String valueText = value.toString().toLowerCase(); // First match against the whole, non-splitted value if (valueText.startsWith(prefixString)) { newValues.add(value); } else { final String[] words = valueText.split(" "); final int wordCount = words.length; // Start at index 0, in case valueText starts with space(s) for (int k = 0; k < wordCount; k++) { if (words[k].startsWith(prefixString)) { newValues.add(value); break; } } } } results.values = newValues; results.count = newValues.size(); } return results; } @Override protected void publishResults(CharSequence constraint, FilterResults results) { //noinspection unchecked mObjects = (List<T>) results.values; if (results.count > 0) { notifyDataSetChanged(); } else { notifyDataSetInvalidated(); } } }
這個ArrayFilter內部類實現了這個Filter抽象類的兩個抽象方法,一個是performFiltering,一個是publishResult,在performFiltering中實現了過濾條件,那麼試想一下,若是公司有搜索聯繫人這麼一個相似須要,佈局大約是上邊一個EditText,下邊是一個ListView,數據都在本地,不用網絡獲取了,那咱們怎麼經過輸入的文字快速的過濾後展現到ListView中呢,那麼這裏就有了思路。code
咱們看一下ArrayFilter中的:orm
final String valueText = value.toString().toLowerCase();
意思就是把bean中的toString方法做爲比較條件,咱們是否是在bean中重寫一些toString方法,而後在EditText的監聽中調用arrayAdapter.getFilter().filter(CharSequence constraint)不就OK了,也有人說了,你本身不會寫個過濾條件啊,可是有現成的爲何不用呢。繼承
此外ArrayAdapter裏還有一些使用的方法,咱們能夠慢慢體會,扔掉那個沒怎麼封裝的BaseAdapter吧。