Create README.md

Author: agustarc

README.md

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+# Android-Kotlin-Extensions
+Useful Kotlin extension functions for Android
+
+## Core
+```kotlin
+inline fun <reified T : Activity> Activity.startActivity() {
+    val intent = Intent()
+    intent.setClass(this, T::class.java)
+    startActivity(intent)
+}
+```
+```kotlin
+val Int.DP
+    get() = TypedValue.applyDimension(
+        TypedValue.COMPLEX_UNIT_DIP,
+        toFloat(),
+        Resources.getSystem().displayMetrics
+    ).toInt()
+
+val Float.DP
+    get() = TypedValue.applyDimension(
+        TypedValue.COMPLEX_UNIT_DIP,
+        this,
+        Resources.getSystem().displayMetrics
+    )
+```
+```kotlin
+val Context.windowManager
+    get() = getSystemService(Context.WINDOW_SERVICE) as WindowManager
+
+val Context.connectivityManager
+    get() = getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
+```
+```kotlin
+inline fun belowApi(api: Int, included: Boolean = false, block: () -> Unit) {
+    if (Build.VERSION.SDK_INT < if (included) api + 1 else api) {
+        block()
+    }
+}
+
+inline fun aboveApi(api: Int, included: Boolean = false, block: () -> Unit) {
+    if (Build.VERSION.SDK_INT > if (included) api - 1 else api) {
+        block()
+    }
+}
+```
+[Show more extensions](https://github.com/AgustaRC/Android-Kotlin-Extensions/tree/master/android-core/src/main/java/github/agustarc/android/extensions/core)
+
+
+## LiveData
+```kotlin
+fun <X, Y> LiveData<X>.map(body: (X) -> Y): LiveData<Y> {
+    return Transformations.map(this, body)
+}
+
+fun <X, Y> LiveData<X>.switchMap(body: (X) -> LiveData<Y>): LiveData<Y> {
+    return Transformations.switchMap(this, body)
+}
+```
+```kotlin
+inline fun <T> LiveData<T>.takeUntil(crossinline predicate: (T?) -> Boolean): LiveData<T> {
+    val mediator = MediatorLiveData<T>()
+    mediator.addSource(this) {
+        if (predicate(it)) {
+            mediator.value = it
+        } else {
+            mediator.removeSource(this)
+        }
+    }
+
+    return mediator
+}
+```
+```kotlin
+fun <A, B, Result> LiveData<A>.combineLatest(
+    other: LiveData<B>,
+    combiner: (A, B) -> Result
+): LiveData<Result> {
+    val mediator = MediatorLiveData<Result>()
+    mediator.addSource(this) { a ->
+        val b = other.value
+        if (b != null) {
+            mediator.value = combiner(a, b)
+        }
+    }
+    mediator.addSource(other) { b ->
+        val a = this@combineLatest.value
+        if (a != null) {
+            mediator.value = combiner(a, b)
+        }
+    }
+    return mediator
+}
+```
+[Show more extensions](https://github.com/AgustaRC/Android-Kotlin-Extensions/tree/master/android-livedata/src/main/java/github/agustarc/android/extensions/livedata)
+
+## View
+```kotlin
+inline fun <T : View> T.afterMeasured(crossinline block: T.() -> Unit) {
+    viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
+        override fun onGlobalLayout() {
+            if (measuredWidth > 0 && measuredHeight > 0) {
+                viewTreeObserver.removeOnGlobalLayoutListener(this)
+                block()
+            }
+        }
+    })
+}
+```
+```kotlin
+fun View.isVisible() = visibility == View.VISIBLE
+
+fun View.isInvisible() = visibility == View.INVISIBLE
+
+fun View.isGone() = visibility == View.GONE
+```
+```kotlin
+fun ViewGroup.inflate(@LayoutRes resId: Int): View =
+    LayoutInflater.from(context).inflate(resId, this, false)
+
+val ViewGroup.children: List<View>
+    get() = (0 until childCount).map { getChildAt(it) }
+
+operator fun ViewGroup.get(index: Int): View? = getChildAt(index)
+
+operator fun ViewGroup.plusAssign(child: View) = addView(child)
+
+operator fun ViewGroup.minusAssign(child: View) = removeView(child)
+
+operator fun ViewGroup.contains(child: View) = indexOfChild(child) != -1
+```
+[Show more extensions](https://github.com/AgustaRC/Android-Kotlin-Extensions/tree/master/android-view/src/main/java/github/agustarc/android/extensions/view)