在Android中两个Activity、Activity与Fragment之间传参是件很痛苦的事情，因为要定义很多的key。步骤也非常的繁琐，要存要取。
现在这个问题有了新的解决方案，就是利用Kotlin的属性代理。
比如有两个Activity，一个是MainActivity，一个是TestActivity，从MainActivity到TestActivity.
class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
findViewById<Button>(R.id.activityBtn).setOnClickListener { //跳转到TestActivity
}
}
}TestActivity代码
class TestActivity : AppCompatActivity() {
var name:String=""
var num:Int=0
private lateinit var textView: TextView
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_test)
textView = findViewById(R.id.textView)
textView.text = "$name - $num"
}
}如果用之前常规的写法是这样的
val intent = Intent(this@MainActivity, TestActivity::class.java);
intent.putExtra("name", "王小二")
intent.putExtra("age", "25")
startActivity(intent)在TestActivity去取参数也麻烦、这里就不贴了
那么新方式是怎么写呢？请看
新写法
跳转的代码
TestActivity().apply {
name = "Come from MainActivity"
num = 100
startActivity(this@MainActivity, this)
}取值的代码
class TestActivity : AppCompatActivity() {
var name by ActivityArgument("default")
var num by ActivityArgument(0)
private lateinit var textView: TextView
override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState)
setContentView(R.layout.activity_test)
textView = findViewById(R.id.textView)
textView.text = "$name - $num"
}
}是不是不用再定义一大堆的静态变量，然后存进去再取出来了，设置一次就可以了。
实现原理
1.提前创建Activity的实例，当系统要创建Activity实例时把我们之前创建的给它（要hook代码，了解Activity启动原理的就很好理解，这里就不说了，网上有很多这方面的资源）
2.利用Kotlin的属性代理
show code
保存Activity实例的单例类
object ActivityInstanceManager { private val activityMap = HashMap<Class<*>, Activity>() fun putActivity(activity: Activity) {
activityMap[activity.javaClass] = activity
} fun getActivity(clazz: Class<*>): Activity? { return activityMap.remove(clazz)
}
}Activity扩展StartActivity方法类
fun Activity.startActivity(activity: Activity, nextActivity: Activity) {
ActivityInstanceManager.putActivity(nextActivity)
activity.startActivity(createIntent(activity, nextActivity))
}
fun Activity.startActivityForResult(activity: Activity, nextActivity: Activity, requestCode: Int) {
ActivityInstanceManager.putActivity(nextActivity)
activity.startActivityForResult(createIntent(activity, nextActivity), requestCode)
}
private fun createIntent(activity: Activity, nextActivity: Activity): Intent {
val intent = IntentInstanceManager.getIntentAndRemove(nextActivity) ?: Intent()
intent.setClass(activity, nextActivity::class.java)
return intent
}属性代理类
class ActivityArgument<T : Any>(private val default: T? = null) : ReadWriteProperty<Activity, T> {
var value: T? = null
override operator fun getValue(thisRef: Activity, property: KProperty<*>): T { if (value == null) {
val args = thisRef.intent.extras
?: throw IllegalStateException("Cannot read property ${property.name} if no arguments have been set") if (args.containsKey(property.name)) {
@Suppress("UNCHECKED_CAST")
value = args.get(property.name) as T
} else {
value = default
}
} return value ?: throw IllegalStateException("Property ${property.name} could not be read")
}
override operator fun setValue(thisRef: Activity, property: KProperty<*>, value: T) {
var intent = IntentInstanceManager.getIntent(thisRef) if (intent == null) {
intent = Intent().apply {
putExtras(Bundle())
}
IntentInstanceManager.putIntent(thisRef, intent)
}
val args = intent.extras
val key = property.name
when (value) {
is String -> args.putString(key, value)
is Int -> args.putInt(key, value)
is Short -> args.putShort(key, value)
is Long -> args.putLong(key, value)
is Byte -> args.putByte(key, value)
is ByteArray -> args.putByteArray(key, value)
is Char -> args.putChar(key, value)
is CharArray -> args.putCharArray(key, value)
is CharSequence -> args.putCharSequence(key, value)
is Float -> args.putFloat(key, value)
is Bundle -> args.putBundle(key, value)
is Binder -> BundleCompat.putBinder(args, key, value)
is android.os.Parcelable -> args.putParcelable(key, value)
is java.io.Serializable -> args.putSerializable(key, value) else -> throw IllegalStateException("Type ${value.javaClass.canonicalName} of property ${property.name} is not supported")
}
intent.putExtras(args)
}
} private val intentMap = HashMap<Activity, Intent>() fun putIntent(activity: Activity, intent: Intent) {
intentMap[activity] = intent
} fun getIntent(activity: Activity): Intent? { return intentMap[activity]
} fun getIntentAndRemove(activity: Activity): Intent? { return intentMap.remove(activity)
} fun removeIntent(activity: Activity) {
intentMap.remove(activity)
}
}好了 核心的就是些
还有的就是hook Instrumentation 类创建Activity
class InstrumentationProxy(val mInstrumentation: Instrumentation) : Instrumentation() {
override fun newActivity(cl: ClassLoader?, className: String?, intent: Intent?): Activity {
println("className = ${className}")
val clazz = Class.forName(className) return ActivityInstanceManager.getActivity(clazz) ?: super.newActivity(cl, className, intent)
}
}替换系统 Instrumentation
private fun hookActivityThreadInstrumentation() { try {
val activityThreadClazz = Class.forName("android.app.ActivityThread")
val activityThreadField = activityThreadClazz.getDeclaredField("sCurrentActivityThread")
activityThreadField.isAccessible = true
val activityThread = activityThreadField.get(null)
val instrumentationField = activityThreadClazz.getDeclaredField("mInstrumentation")
instrumentationField.isAccessible = true
val instrumentation = instrumentationField.get(activityThread) as Instrumentation
val proxy = InstrumentationProxy(instrumentation)
instrumentationField.set(activityThread, proxy)
} catch (e: Exception) {
e.printStackTrace()
}
}这样就能把我们提前创建的Activity的实例给系统了
到这里就完了 以后启动Activity就可以这样写了
TestActivity().apply {
name = "Come from MainActivity"
num = 100
startActivity(this@MainActivity, this)
}是不是可以提前下班、、、
Fragment也是一样的，因为不需要hook 就更简单了
class TestFragment : Fragment() {
companion object { fun attach(act: FragmentActivity, containerId: Int) {
val fragment = TestFragment().apply {
age = 18
name = "小花"
}
act.supportFragmentManager.beginTransaction().replace(containerId, fragment).commit()
}
}
var name by FragmentArgument("lily")
var age by FragmentArgument(16)
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? { return inflater.inflate(R.layout.fragment_test, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
val textView = view!!.findViewById<TextView>(R.id.contentTv)
textView.text = "$name - $age"
}
}看下代码就明白了
属性代理还有SharedPreferences 的应用
可以这样写
private var keystore by PreferenceArgument(this, "keystore", "abc")
原理是一样的 就贴下代码吧
class PreferenceArgument<T>(context: Context, private val name: String, private val default: T) :
ReadWriteProperty<Any?, T> {
private val prefs by lazy {
context.getSharedPreferences("${context.packageName}_preferences", Context.MODE_PRIVATE)
}
override fun getValue(thisRef: Any?, property: KProperty<*>): T = findPreferences(name, default)
override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
putPreferences(name, value)
}
private fun putPreferences(name: String, value: T) = with(prefs.edit()) {
when (value) {
is Int -> putInt(name, value)
is Long -> putLong(name, value)
is Float -> putFloat(name, value)
is String -> putString(name, value)
is Boolean -> putBoolean(name, value) else ->
throw IllegalArgumentException("This type can not be saved into preferences")
}
apply()
}
private fun findPreferences(name: String, default: T) = with(prefs) {
var result = when (default) {
is Int -> getInt(name, default)
is Long -> getLong(name, default)
is Float -> getFloat(name, default)
is String -> getString(name, default)
is Boolean -> getBoolean(name, default) else ->
throw IllegalArgumentException("This type can not be saved into preferences")
}
result as T
}
}
作者：蓦然地执着
链接：https://www.jianshu.com/p/3506e3c9ec50
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