ListActivity源码分析
来源:互联网 发布:数字网络意思大全 编辑:程序博客网 时间:2024/06/05 20:31
Android中的ListActivity其实就是一个自带ListView的Activity,ListActivity它位于命名空间:android.app之下,从它的源代码就可以清楚的看到,ListActivity继承了Activity,它的基本用法网上有很多资料,随便GOOGLE一下,到处都是,下面主要是分析一下它的Java源代码.
public
class
ListActivity
extends
Activity {
/**
* This field should be made private, so it is hidden from the SDK.
* {@hide}
*/
protected
ListAdapter mAdapter;
/**
* This field should be made private, so it is hidden from the SDK.
* {@hide}
*/
protected
ListView mList;
private
Handler mHandler =
new
Handler();
private
boolean
mFinishedStart =
false
;
private
Runnable mRequestFocus =
new
Runnable() {
public
void
run() {
mList.focusableViewAvailable(mList);
}
};
/**
* This method will be called when an item in the list is selected.
* Subclasses should override. Subclasses can call
* getListView().getItemAtPosition(position) if they need to access the
* data associated with the selected item.
*
* @param l The ListView where the click happened
* @param v The view that was clicked within the ListView
* @param position The position of the view in the list
* @param id The row id of the item that was clicked
*/
protected
void
onListItemClick(ListView l, View v,
int
position,
long
id) {
}
/**
* Ensures the list view has been created before Activity restores all
* of the view states.
*
*@see Activity#onRestoreInstanceState(Bundle)
*/
@Override
protected
void
onRestoreInstanceState(Bundle state) {
ensureList();
super
.onRestoreInstanceState(state);
}
/**
* @see Activity#onDestroy()
*/
@Override
protected
void
onDestroy() {
mHandler.removeCallbacks(mRequestFocus);
super
.onDestroy();
}
/**
* Updates the screen state (current list and other views) when the
* content changes.
*
* @see Activity#onContentChanged()
*/
@Override
public
void
onContentChanged() {
super
.onContentChanged();
View emptyView = findViewById(com.android.internal.R.id.empty);
mList = (ListView)findViewById(com.android.internal.R.id.list);
if
(mList ==
null
) {
throw
new
RuntimeException(
"Your content must have a ListView whose id attribute is "
+
"'android.R.id.list'"
);
}
if
(emptyView !=
null
) {
mList.setEmptyView(emptyView);
}
mList.setOnItemClickListener(mOnClickListener);
if
(mFinishedStart) {
setListAdapter(mAdapter);
}
mHandler.post(mRequestFocus);
mFinishedStart =
true
;
}
/**
* Provide the cursor for the list view.
*/
public
void
setListAdapter(ListAdapter adapter) {
synchronized
(
this
) {
ensureList();
mAdapter = adapter;
mList.setAdapter(adapter);
}
}
/**
* Set the currently selected list item to the specified
* position with the adapter's data
*
* @param position
*/
public
void
setSelection(
int
position) {
mList.setSelection(position);
}
/**
* Get the position of the currently selected list item.
*/
public
int
getSelectedItemPosition() {
return
mList.getSelectedItemPosition();
}
/**
* Get the cursor row ID of the currently selected list item.
*/
public
long
getSelectedItemId() {
return
mList.getSelectedItemId();
}
/**
* Get the activity's list view widget.
*/
public
ListView getListView() {
ensureList();
return
mList;
}
/**
* Get the ListAdapter associated with this activity's ListView.
*/
public
ListAdapter getListAdapter() {
return
mAdapter;
}
private
void
ensureList() {
if
(mList !=
null
) {
return
;
}
setContentView(com.android.internal.R.layout.list_content_simple);
}
private
AdapterView.OnItemClickListener mOnClickListener =
new
AdapterView.OnItemClickListener() {
public
void
onItemClick(AdapterView<?> parent, View v,
int
position,
long
id)
{
onListItemClick((ListView)parent, v, position, id);
}
};
}
代码如上,在使用ListActivity时,一般用 this.setListAdapter()传入一个ListAdapter,用来绑定ListActivity中的ListView,当调用setListAdapter()时,在ListActivity内部,会调用如下方法:
/**
* Provide the cursor for the list view.
*/
public void setListAdapter(ListAdapter adapter) {
synchronized (this) {
ensureList();
mAdapter = adapter;
mList.setAdapter(adapter);
}
}
其中ensureList();是一个比较重要的方法,可以查看源代码知道,mList其实就是ListActivity中的ListView了,
接下来会调用ensureList(),先看下它是怎么弄的吧:
private void ensureList() {
if (mList != null) {
return;
}
setContentView(com.android.internal.R.layout.list_content_simple);
}
可以看到,原来,就是在这里,setContentView()引入了一个名叫com.android.internal.R.layout.list_content_simple的布局资源,这个资源,就位于我们的d:\AndroidSDK\platforms\android-16\data\res\layout下的list_content_simple.xml布局文件,用ECLIPSE打开这个布局文件看下吧。
<ListView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@android:id/list"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:drawSelectorOnTop="false"
/>
原来这个ListView的ID就是android:id="@android:id/list",所以在这里如果我们要自定义LISTVIEW的布局文件时,这个LISTVIEW的ID就必须取名为:android:id="@android:id/list"啦,呵呵。
继续往下分析,当调用 setContentView(com.android.internal.R.layout.list_content_simple)这段代码后,接下来会调用onContentChanged(),这个方法是用来干嘛的呢,看下它的英文注释:
/**
* Updates the screen state (current list and other views) when the
* content changes.
*
* @see Activity#onContentChanged()
*/
原来就是当这个Activity内容发生改变时,就会调用。
@Override
public void onContentChanged() {
super.onContentChanged(); //调用基类的onContentChanged
View emptyView = findViewById(com.android.internal.R.id.empty); //查找ID为com.android.internal.R.id.empty的VIEW,这个VIEW一般用来当LISTVIEW没有任何ITEM时,显示一条信息。
mList = (ListView)findViewById(com.android.internal.R.id.list);//查找ID为com.android.internal.R.id.list的LISTVIEW
if (mList == null) {
throw new RuntimeException(
"Your content must have a ListView whose id attribute is " +
"'android.R.id.list'");
}
if (emptyView != null) {
mList.setEmptyView(emptyView); //setEmptyView()这个方法不是LISTACTIVITY的,而是它的父父类AdapterView的,这里的AdapterView是一个抽象类,其官方的定义是:“An AdapterView is a view whose children are determined by an Adapter.”,意思为:她是一个VIEW,什么VIEW呢?是它的子项需要一个适配器ADAPTER来填充的VIEW.
}
mList.setOnItemClickListener(mOnClickListener);//LISTVIEW的ITEM选中的回调方法
if (mFinishedStart) {
setListAdapter(mAdapter);
}
mHandler.post(mRequestFocus); //Handler,这里把一个类型为Runnable的玩意儿投放到了消息队列里面,待主线程来处理。其中mRequestFocus是用来使ListView获取焦点的。
mFinishedStart = true;
}
- ListActivity源码分析
- Android ListActivity和实例分析
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity---
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- ListActivity
- 草根站长胖子讲述做站故事
- 一些开源项目网址
- PAIP.ecshop file_put_contents Warning notice解决方法
- linux下查看文件和文件夹大小
- [设计模式]适配器模式(Adapter)
- ListActivity源码分析
- Eclipse Preferences的设置
- 【转】Java:Session详解
- Juniper monitor interface
- webkit 详解
- modelsim error:'rom_nxm_tb' already exists and will be overwritten
- VC中DLL、OCX中获取本身完整路径
- POJ3041《Asteroids》方法:匈牙利算法(最小点覆盖数==最大二分匹配数)
- Linux Kernel Source - 进程哈希表浅析