一个android app界面由布局加控件组成,初期写代码,都会大量的使用findViewById和setOnClickeListener,控件较多时就会显得繁琐冗余。
示例如下:
userName = (EditText)this.findViewById(R.id.userName);
userPwd = (EditText)this.findViewById(R.id.userPwd);
CheckBox checkBox = (CheckBox) findViewById(R.id.login_check);
mClear1 = (ImageButton)findViewById(R.id.clearName);
mClear2 = (ImageButton)findViewById(R.id.clearPwd);
loginBtn = (Button)this.findViewById(R.id.loginBtn);
Button register = (Button)this.findViewById(R.id.registerBtn);
loginBtn.setOnClickListener(new LoginOnClickListener());
今天我们要讨论的内容则可以很好的解决这个问题,那就是大名鼎鼎的反转控制IOC(Inversion of Control),声明控件变量时使用注解(详见http://blog.youkuaiyun.com/beyond0851/article/details/8520993),利用反射(详见http://blog.youkuaiyun.com/tiananma0607/article/details/49002089)实现注入
了解注解:
从jdk1.5开始,Java提供了注解的功能,允许开发者定义和使用自己的注解类型,该功能由一个定义注解类型的语法和描述一个注解声明的语法,读取注解的API,一个使用注解修饰的class文件和一个注解处理工具组成。
首先,你需要接受一个关键字@interface ,噢,它可不是接口定义关键字,更不是OC里面的@interface关键字,是Java中表示声明一个注解类的关键字。
使用@interface 表示我们已经继承了java.lang.annotation.Annotation类,这是一个注解的基类接口,就好像Object类,现在你只需要知道它的存在就行了。
还有一条规定:在定义注解时,不能继承其他的注解或接口。
那么,这就是最简单的一个注解类
1
2
3
|
public
@interface
MyAnnotation {
}
|
然而通常在使用时我们都会给这个注解类加上两个注解:
@Target(ElementType.FIELD)、@Retention(RetentionPolicy.RUNTIME)
ElementType、RetentionPolicy是两个枚举类,ElementType.FIELD表示我们需要注解的是一个字段,以下是摘自JDK1.6文档中的介绍:
使用注解:
以下为KJFrameForAndroid框架中绑定控件注解部分的定义与使用:
1
2
3
4
5
6
|
@Target
(ElementType.FIELD)
@Retention
(RetentionPolicy.RUNTIME)
public
@interface
BindView {
public
int
id();
public
boolean
click()
default
false
;
}
|
1
2
|
@BindView
(id = R.id.x, click =
true
)
private
TextView t;
|
我们可以看到,除了明显减少了代码量,还使得代码结构更加清晰。
其中,定义部分的id() 表示注解接受一个int类型的数据作为id所对应的值(就如使用中的id = R.id.xxx);
同理,定义部分的click表示接受一个Boolean类型的数据作为click对应的值,还可以设置一个默认值使用default修饰;
处理注解:
我们已经知道了注解怎么定义和使用,接下来就应该知道怎么处理了。
上面已经说了,bindview注解可以接受一个int类型的值和一个Boolean类型的值,那么这两个值接受了以后如何获取呢?
其实获取的方式很简单就是通过一个BindView类型的对象,调用这个对象来自声明中定义的两个方法——>id()或click()方法。
现在就有一个问题了,注解类型是不能直接new对象的,那么这个BindView对象从哪里来呢?
这时就需要用到Java的反射机制。我们知道,每一个继承自Object类的类都会继承一个getClass()方法,下面看一下这个方法的原型:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
|
/**
* Returns the unique instance of {@link Class} that represents this
* object's class. Note that {@code getClass()} is a special case in that it
* actually returns {@code Class<? extends Foo>} where {@code Foo} is the
* erasure of the type of the expression {@code getClass()} was called upon.
* <p>
* As an example, the following code actually compiles, although one might
* think it shouldn't:
* <p>
* <pre>{@code
* List<Integer> l = new ArrayList<Integer>();
* Class<? extends List> c = l.getClass();}</pre>
*
* @return this object's {@code Class} instance.
*/
public
final
native
Class<?> getClass();
|
是一个native方法,根据注释我们知道,这个方法返回的是该类的Class对象,同时也是该类的二进制对象。
Class中有一个方法叫getDeclaredFields(),是用来返回这个类的全部字段,返回类型是Field[]
通过Field对象的getAnnotation(Class<?>)方法,我们可以获取到任何一个Class的对象,通过getAnnotation(Class<?>),我们就可以获取到BindView的对象了。
例如:
1
2
3
4
5
6
7
8
9
|
Field[] fields = currentClass.getClass().getDeclaredFields();
for
(
int
i =
0
; i < fields.length; i++){
BindView bindView = field.getAnnotation(BindView.
class
);
int
viewId = bindView.id();
//这是我们传的id
boolean
clickLis = bindView.click();
//这是我们传的click
}
|
在有上面的知识准备后,接下来我们动手写一个类似的IOC框架(同时绑定VIEW和事件)
1,View注解类
// TODO: Auto-generated Javadoc
/**
* The Interface AfIocView.
*/
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface AfIocView {
/**
* Id.
*
* @return the int
*/
public int id();
/**
* Click.
*
* @return the string
*/
public String click() default "";
/**
* Long click.
*
* @return the string
*/
public String longClick() default "";
/**
* Item click.
*
* @return the string
*/
public String itemClick() default "";
/**
* Item long click.
*
* @return the string
*/
public String itemLongClick() default "";
/**
* Select.
*
* @return the ab ioc select
*/
public AfIocSelect select() default @AfIocSelect(selected="") ;
}
2,Event事件监听类
<pre name="code" class="java">public class AfIocEventListener implements OnClickListener, OnLongClickListener, OnItemClickListener, OnItemSelectedListener,OnItemLongClickListener {
/** The handler. */
private Object handler;
/** The click method. */
private String clickMethod;
/** The long click method. */
private String longClickMethod;
/** The item click method. */
private String itemClickMethod;
/** The item select method. */
private String itemSelectMethod;
/** The nothing selected method. */
private String nothingSelectedMethod;
/** The item long click mehtod. */
private String itemLongClickMehtod;
/** The Constant CLICK. */
public static final int CLICK = 0;
/** The Constant LONGCLICK. */
public static final int LONGCLICK = 1;
/** The Constant ITEMCLICK. */
public static final int ITEMCLICK = 2;
/** The Constant ITEMLONGCLICK. */
public static final int ITEMLONGCLICK = 3;
/**
* Instantiates a new ab ioc event listener.
*
* @param handler the handler
*/
public AfIocEventListener(Object handler) {
this.handler = handler;
}
/**
* Click.
*
* @param method the method
* @return the ab ioc event listener
*/
public AfIocEventListener click(String method){
this.clickMethod = method;
return this;
}
/**
* Long click.
*
* @param method the method
* @return the ab ioc event listener
*/
public AfIocEventListener longClick(String method){
this.longClickMethod = method;
return this;
}
/**
* Item long click.
*
* @param method the method
* @return the ab ioc event listener
*/
public AfIocEventListener itemLongClick(String method){
this.itemLongClickMehtod = method;
return this;
}
/**
* Item click.
*
* @param method the method
* @return the ab ioc event listener
*/
public AfIocEventListener itemClick(String method){
this.itemClickMethod = method;
return this;
}
/**
* Select.
*
* @param method the method
* @return the ab ioc event listener
*/
public AfIocEventListener select(String method){
this.itemSelectMethod = method;
return this;
}
/**
* No select.
*
* @param method the method
* @return the ab ioc event listener
*/
public AfIocEventListener noSelect(String method){
this.nothingSelectedMethod = method;
return this;
}
/* (non-Javadoc)
* @see android.view.View.OnLongClickListener#onLongClick(android.view.View)
*/
public boolean onLongClick(View v) {
return invokeLongClickMethod(handler,longClickMethod,v);
}
/* (non-Javadoc)
* @see android.widget.AdapterView.OnItemLongClickListener#onItemLongClick(android.widget.AdapterView, android.view.View, int, long)
*/
public boolean onItemLongClick(AdapterView<?> arg0, View arg1, int arg2,long arg3) {
return invokeItemLongClickMethod(handler,itemLongClickMehtod,arg0,arg1,arg2,arg3);
}
/* (non-Javadoc)
* @see android.widget.AdapterView.OnItemSelectedListener#onItemSelected(android.widget.AdapterView, android.view.View, int, long)
*/
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,long arg3) {
invokeItemSelectMethod(handler,itemSelectMethod,arg0,arg1,arg2,arg3);
}
/* (non-Javadoc)
* @see android.widget.AdapterView.OnItemSelectedListener#onNothingSelected(android.widget.AdapterView)
*/
public void onNothingSelected(AdapterView<?> arg0) {
invokeNoSelectMethod(handler,nothingSelectedMethod,arg0);
}
/* (non-Javadoc)
* @see android.widget.AdapterView.OnItemClickListener#onItemClick(android.widget.AdapterView, android.view.View, int, long)
*/
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
invokeItemClickMethod(handler,itemClickMethod,arg0,arg1,arg2,arg3);
}
/* (non-Javadoc)
* @see android.view.View.OnClickListener#onClick(android.view.View)
*/
public void onClick(View v) {
invokeClickMethod(handler, clickMethod, v);
}
/**
* Invoke click method.
*
* @param handler the handler
* @param methodName the method name
* @param params the params
* @return the object
*/
private Object invokeClickMethod(Object handler, String methodName, Object... params){
if(handler == null) return null;
Method method = null;
try{
method = handler.getClass().getDeclaredMethod(methodName,View.class);
if(method!=null)
return method.invoke(handler, params);
else
throw new AfAppException("no such method:"+methodName);
}catch(Exception e){
e.printStackTrace();
}
return null;
}
/**
* Invoke long click method.
*
* @param handler the handler
* @param methodName the method name
* @param params the params
* @return true, if successful
*/
private boolean invokeLongClickMethod(Object handler, String methodName, Object... params){
if(handler == null) return false;
Method method = null;
try{
//public boolean onLongClick(View v)
method = handler.getClass().getDeclaredMethod(methodName,View.class);
if(method!=null){
Object obj = method.invoke(handler, params);
return obj==null?false:Boolean.valueOf(obj.toString());
}
else
throw new AfAppException("no such method:"+methodName);
}catch(Exception e){
e.printStackTrace();
}
return false;
}
/**
* Invoke item click method.
*
* @param handler the handler
* @param methodName the method name
* @param params the params
* @return the object
*/
private Object invokeItemClickMethod(Object handler, String methodName, Object... params){
if(handler == null) return null;
Method method = null;
try{
///onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3)
method = handler.getClass().getDeclaredMethod(methodName,AdapterView.class,View.class,int.class,long.class);
if(method!=null)
return method.invoke(handler, params);
else
throw new AfAppException("no such method:"+methodName);
}catch(Exception e){
e.printStackTrace();
}
return null;
}
/**
* Invoke item long click method.
*
* @param handler the handler
* @param methodName the method name
* @param params the params
* @return true, if successful
*/
private boolean invokeItemLongClickMethod(Object handler, String methodName, Object... params){
Method method = null;
try{
if(handler == null){
throw new AfAppException("invokeItemLongClickMethod: handler is null :");
}
///onItemLongClick(AdapterView<?> arg0, View arg1, int arg2,long arg3)
method = handler.getClass().getDeclaredMethod(methodName,AdapterView.class,View.class,int.class,long.class);
if(method!=null){
Object obj = method.invoke(handler, params);
return Boolean.valueOf(obj==null?false:Boolean.valueOf(obj.toString()));
}
else
throw new AfAppException("no such method:"+methodName);
}catch(Exception e){
e.printStackTrace();
}
return false;
}
/**
* Invoke item select method.
*
* @param handler the handler
* @param methodName the method name
* @param params the params
* @return the object
*/
private Object invokeItemSelectMethod(Object handler, String methodName, Object... params){
if(handler == null) return null;
Method method = null;
try{
///onItemSelected(AdapterView<?> arg0, View arg1, int arg2,long arg3)
method = handler.getClass().getDeclaredMethod(methodName,AdapterView.class,View.class,int.class,long.class);
if(method!=null)
return method.invoke(handler, params);
else
throw new AfAppException("no such method:"+methodName);
}catch(Exception e){
e.printStackTrace();
}
return null;
}
/**
* Invoke no select method.
*
* @param handler the handler
* @param methodName the method name
* @param params the params
* @return the object
*/
private Object invokeNoSelectMethod(Object handler, String methodName, Object... params){
if(handler == null) return null;
Method method = null;
try{
//onNothingSelected(AdapterView<?> arg0)
method = handler.getClass().getDeclaredMethod(methodName,AdapterView.class);
if(method!=null)
return method.invoke(handler, params);
else
throw new AfAppException("no such method:"+methodName);
}catch(Exception e){
e.printStackTrace();
}
return null;
}
3,初始化IOC控制,实现View与事件注入
/**
* 初始化为IOC控制的View.
*/
private void initIocView(){
Field[] fields = getClass().getDeclaredFields();
if(fields!=null && fields.length>0){
for(Field field : fields){
try {
field.setAccessible(true);
if(field.get(this)!= null )
continue;
AfIocView viewInject = field.getAnnotation(AfIocView.class);
if(viewInject!=null){
int viewId = viewInject.id();
field.set(this,findViewById(viewId));
setListener(field,viewInject.click(),AfIocEventListener.CLICK);
setListener(field,viewInject.longClick(),AfIocEventListener.LONGCLICK);
setListener(field,viewInject.itemClick(),AfIocEventListener.ITEMCLICK);
setListener(field,viewInject.itemLongClick(),AfIocEventListener.ITEMLONGCLICK);
AfIocSelect select = viewInject.select();
if(!TextUtils.isEmpty(select.selected())){
setViewSelectListener(field,select.selected(),select.noSelected());
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
/**
* 设置view的监听器.
*
* @param field the field
* @param select the select
* @param noSelect the no select
* @throws Exception the exception
*/
private void setViewSelectListener(Field field,String select,String noSelect)throws Exception{
Object obj = field.get(this);
if(obj instanceof View){
((AbsListView)obj).setOnItemSelectedListener(new AfIocEventListener(this).select(select).noSelect(noSelect));
}
}
/**
* 设置view的监听器.
*
* @param field the field
* @param methodName the method name
* @param method the method
* @throws Exception the exception
*/
private void setListener(Field field,String methodName,int method)throws Exception{
if(methodName == null || methodName.trim().length() == 0)
return;
Object obj = field.get(this);
switch (method) {
case AfIocEventListener.CLICK:
if(obj instanceof View){
((View)obj).setOnClickListener(new AfIocEventListener(this).click(methodName));
}
break;
case AfIocEventListener.ITEMCLICK:
if(obj instanceof AbsListView){
((AbsListView)obj).setOnItemClickListener(new AfIocEventListener(this).itemClick(methodName));
}
break;
case AfIocEventListener.LONGCLICK:
if(obj instanceof View){
((View)obj).setOnLongClickListener(new AfIocEventListener(this).longClick(methodName));
}
break;
case AfIocEventListener.ITEMLONGCLICK:
if(obj instanceof AbsListView){
((AbsListView)obj).setOnItemLongClickListener(new AfIocEventListener(this).itemLongClick(methodName));
}
break;
default:
break;
}
}
4,在Activity中使用示例如下:
@AfIocView(id = R.id.mBtn,click="btnClick")Button button;
@AfIocView(id = R.id.mText)TextView mTextView;
点击Button控件时就会调用注解里的btnClick方法,从此findViewById和事件处理写起来会简洁清楚许多