目录
一、思路
viewmodel对象是存储在viewmodelstore中的，那么如果我们创建一个全局使用的viewmodelstore并且在获取viewmodel对象的时候从它里面获取就可以了。
viewmodel是通过viewmodelprovider的get方法获取的，一般是viewmodelprovider(owner: viewmodelstoreowner, factory: factory).get(viewmodel::class.java)。
如何将viewmodelprovider与viewmodelstore关联起来? 纽带就是viewmodelstoreowner, viewmodelstoreowner是一个接口，需要实现getviewmodelstore()方法，而该方法返回的就是viewmodelstore:
public interface viewmodelstoreowner {
/**
* returns owned {@link viewmodelstore}
*
* @return a {@code viewmodelstore}
*/
@nonnull
viewmodelstore getviewmodelstore(); //返回一个viewmodelstore
}
让某个类实现这个接口，重写方法返回我们定义的viewmodelstore就可以了。
至于上面viewmodelprovider构造方法的第二个参数factory是什么呢?
源码中提供了二种factory，一种是newinstancefactory，一种是androidviewmodelfactory，它们的主要区别是：
newinstancefactory创建viewmodel时，会为每个activity或fragment创建一个新的viewmodel实例，这会导致viewmodel无法在应用程序的不同部分共享数据。（componentactivity源码getdefaultviewmodelproviderfactory方法）
androidviewmodelfactory可以访问应用程序的全局状态，并且viewmodel实例可以在整个应用程序中是共享的。
根据我们的需求，需要用的是androidviewmodelfactory。
二、具体实现
1、方式一：可以全局添加和获取任意viewmodel
定义application，ktx.kt文件
import android.app.application
lateinit var appcontext: application
fun setapplicationcontext(context: application) {
appcontext = context
}
定义全局可用的viewmodelowner实现类
object applicationscopeviewmodelprovider : viewmodelstoreowner {
private val eventviewmodelstore: viewmodelstore = viewmodelstore()
override fun getviewmodelstore(): viewmodelstore {
return eventviewmodelstore
}
private val mapplicationprovider: viewmodelprovider by lazy {
viewmodelprovider(
applicationscopeviewmodelprovider,
viewmodelprovider.androidviewmodelfactory.getinstance(appcontext)
)
}
fun getapplicationscopeviewmodel(modelclass: class): t {
return mapplicationprovider.get(modelclass)
}
}
定义一个viewmodel通过stateflow定义发送和订阅事件的方法
class eventviewmodel : viewmodel() {
private val mutablestateflow = mutablestateflow(0)
fun postevent(state: int) {
mutablestateflow.value = state
}
fun observeevent(scope: coroutinescope? = null, method: (int) -> unit = { _ -> }) {
val eventscope = scope ?: viewmodelscope
eventscope.launch {
mutablestateflow.collect {
method.invoke(it)
}
}
}
}
定义一个调用的类
object flowevent {
//发送事件
fun postevent(state: int) {
applicationscopeviewmodelprovider.getapplicationscopeviewmodel(eventviewmodel::class.java)
.postevent(state)
}
//订阅事件
fun observeevent(scope: coroutinescope? = null, method: (int) -> unit = { _ -> }) {
applicationscopeviewmodelprovider.getapplicationscopeviewmodel(eventviewmodel::class.java)
.observeevent(scope, method)
}
}
测试代码如下:
class mainactivity : appcompatactivity() {
override fun oncreate(savedinstancestate: bundle?) {
super.oncreate(savedinstancestate)
setcontentview(r.layout.activity_main)
//打印协程名称
system.setproperty("kotlinx.coroutines.debug", "on")
flowevent.observeevent {
printmsg("mainactivity observeevent before :$it")
}
//修改值
flowevent.postevent(1)
flowevent.observeevent {
printmsg("mainactivity observeevent after :$it")
}
}
}
//日志
内容:mainactivity observeevent before :0 线程:main @coroutine#1
内容:mainactivity observeevent before :1 线程:main @coroutine#1
内容:mainactivity observeevent after :1 线程:main @coroutine#2
2、方式二：更方便在activity和fragment中调用
定义application，让baseapplication实现viewmodelstoreowner
//baseapplication实现viewmodelstoreowner接口
class baseapplication : application(), viewmodelstoreowner {
private lateinit var mappviewmodelstore: viewmodelstore
private var mfactory: viewmodelprovider.factory? = null
override fun oncreate() {
super.oncreate()
//设置全局的上下文
setapplicationcontext(this)
//创建viewmodelstore
mappviewmodelstore = viewmodelstore()
}
override fun getviewmodelstore(): viewmodelstore = mappviewmodelstore
/**
* 获取一个全局的viewmodel
*/
fun getappviewmodelprovider(): viewmodelprovider {
return viewmodelprovider(this, this.getappfactory())
}
private fun getappfactory(): viewmodelprovider.factory {
if (mfactory == null) {
mfactory = viewmodelprovider.androidviewmodelfactory.getinstance(this)
}
return mfactory as viewmodelprovider.factory
}
}
ktx.kt文件也有变化，如下
lateinit var appcontext: application
fun setapplicationcontext(context: application) {
appcontext = context
}
//定义扩展方法
inline fun fragment.getappviewmodel(): vm {
(this.requireactivity().application as? baseapplication).let {
if (it == null) {
throw nullpointerexception("application does not inherit from baseapplication")
} else {
return it.getappviewmodelprovider().get(vm::class.java)
}
}
}
//定义扩展方法
inline fun appcompatactivity.getappviewmodel(): vm {
(this.application as? baseapplication).let {
if (it == null) {
throw nullpointerexception("application does not inherit from baseapplication")
} else {
return it.getappviewmodelprovider().get(vm::class.java)
}
}
}
在baseactivity和basefragment中调用上述扩展方法
abstract class baseactivity: appcompatactivity() {
//创建viewmodel对象
val eventviewmodel: eventviewmodel by lazy { getappviewmodel() }
override fun oncreate(savedinstancestate: bundle?) {
super.oncreate(savedinstancestate)
}
}
abstract class basefragment: fragment() {
//创建viewmodel对象
val eventviewmodel: eventviewmodel by lazy { getappviewmodel() }
override fun oncreate(savedinstancestate: bundle?) {
super.oncreate(savedinstancestate)
}
}
测试代码
class mainactivity : baseactivity() {
override fun oncreate(savedinstancestate: bundle?) {
super.oncreate(savedinstancestate)
setcontentview(r.layout.activity_main)
//打印协程名称
system.setproperty("kotlinx.coroutines.debug", "on")
eventviewmodel.observeevent {
printmsg("mainactivity observeevent :$it")
}
findviewbyid(r.id.bt).setonclicklistener {
//点击按钮修改值
eventviewmodel.postevent(1)
//跳转到其他activity
intent(this, twoactivity::class.java).also { startactivity(it) }
}
}
}
class twoactivity : baseactivity() {
override fun oncreate(savedinstancestate: bundle?) {
super.oncreate(savedinstancestate)
setcontentview(r.layout.activity_two)
eventviewmodel.observeevent {
printmsg("twoactivity observeevent :$it")
}
}
}
日志
内容:mainactivity observeevent :0 线程:main @coroutine#1 内容:mainactivity observeevent :1 线程:main @coroutine#1 内容:twoactivity observeevent :1 线程:main @coroutine#2
以上就是详解android如何设计一个全局可调用的viewmodel对象的详细内容，更多关于android viewmodel对象的资料请关注其它相关文章！
