add Tutorial4_1_2SnapshotMutationPolicy

Author: SmartToolFactory

Diff for: Tutorial1-1Basics/src/main/java/com/smarttoolfactory/tutorial1_1basics/chapter4_state/Tutorial4_1_2SnapshotMutationPolicy.kt

@@ -0,0 +1,169 @@
+package com.smarttoolfactory.tutorial1_1basics.chapter4_state
+
+import android.widget.Toast
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material.Button
+import androidx.compose.material.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.referentialEqualityPolicy
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.runtime.structuralEqualityPolicy
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.tooling.preview.Preview
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.smarttoolfactory.tutorial1_1basics.ui.Blue400
+import com.smarttoolfactory.tutorial1_1basics.ui.Orange400
+import com.smarttoolfactory.tutorial1_1basics.ui.components.StyleableTutorialText
+import com.smarttoolfactory.tutorial1_1basics.ui.components.getRandomColor
+
+@Preview
+@Composable
+fun Tutorial4_1Screen2() {
+    TutorialContent()
+}
+
+@Composable
+private fun TutorialContent() {
+    Column(
+        modifier = Modifier
+            .fillMaxSize()
+            .padding(8.dp)
+    ) {
+
+
+        StyleableTutorialText(
+            text = "SnapshotMutationPolicy controls how changes are handled in mutable " +
+                    "snapshots. **structuralEqualityPolicy**(default) policy check " +
+                    "if equals function of a class returns true.\n" +
+                    "**copy function** of **data class** with same message returns equals so " +
+                    "no recomposition is triggered. In first example recomposition is " +
+                    "not trigger when we copy a new object since data class checks primary " +
+                    "constructor values in **equals** functions",
+            bullets = false
+        )
+
+        StructuralEqualitySample()
+        StyleableTutorialText(
+            text =
+            "**referentialEqualityPolicy** policy checks if both instances are the same" +
+                    " to trigger recomposition.\n" +
+                    "Since new instance is created with copy each time button is clicked " +
+                    "new one time event is fired. Border of Text changes on each recomposition " +
+                    "with a random color to show recomposition visually.",
+            bullets = false
+        )
+        ReferentialEqualitySample()
+    }
+}
+
+@Composable
+private fun StructuralEqualitySample() {
+
+    val context = LocalContext.current
+
+    var oneTimeEventData by remember {
+        mutableStateOf(
+            value = OneTimeEventData(message = "structuralEqualityPolicy message"),
+            // 🔥 For recomposition to be triggered we need to assign an object with
+            // different message since data class checks primary constructor values
+            // for equals function
+            policy = structuralEqualityPolicy()
+        )
+    }
+
+    // This is for showing toast message only on each recomposition
+    Toast.makeText(context, oneTimeEventData.message, Toast.LENGTH_SHORT).show()
+
+    Column(
+        modifier = Modifier
+            .background(Orange400)
+            .fillMaxWidth()
+            .padding(4.dp)
+    ) {
+
+        Button(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(vertical = 4.dp),
+            onClick = {
+                oneTimeEventData =
+                    oneTimeEventData.copy(message = "structuralEqualityPolicy message")
+
+            }
+        ) {
+            Text(text = "Click to create Event")
+        }
+
+        Text(
+            modifier = Modifier
+                .border(2.dp, getRandomColor())
+                .fillMaxWidth()
+                .padding(10.dp),
+            text = oneTimeEventData.message,
+            color = Color.White,
+            fontSize = 16.sp
+        )
+    }
+
+}
+
+@Composable
+private fun ReferentialEqualitySample() {
+
+    val context = LocalContext.current
+
+
+    var oneTimeEventData by remember {
+        mutableStateOf(
+            value = OneTimeEventData(message = "referentialEqualityPolicy message"),
+            policy = referentialEqualityPolicy()
+        )
+    }
+
+    Toast.makeText(context, oneTimeEventData.message, Toast.LENGTH_SHORT).show()
+
+    Column(
+        modifier = Modifier
+            .background(Blue400)
+            .fillMaxWidth()
+            .padding(4.dp)
+    ) {
+
+        Button(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(vertical = 4.dp),
+            onClick = {
+                oneTimeEventData =
+                    oneTimeEventData.copy(message = "referentialEqualityPolicy message")
+
+            }
+        ) {
+            Text(text = "Click to create Event")
+        }
+
+        Text(
+            modifier = Modifier
+                .border(2.dp, getRandomColor())
+                .fillMaxWidth()
+                .padding(10.dp),
+            text = oneTimeEventData.message,
+            color = Color.White,
+            fontSize = 16.sp
+        )
+
+    }
+}
+
+private data class OneTimeEventData(val message: String)