[refactor] Improve editor view model readability and fun call frequency

app/src/main/java/com/csapp/sqli/model/LineNumber.kt

@@ -1,5 +1,6 @@
 package com.csapp.sqli.model
 
 data class LineNumber(
-    var content: String,
+    var number: Int = 0,
+    var content: String = "",
 )

app/src/main/java/com/csapp/sqli/view/EditorActivity.kt

@@ -23,7 +23,7 @@ class EditorActivity : AppCompatActivity() {
         binding = DataBindingUtil.setContentView(this, R.layout.activity_editor)
         binding.lifecycleOwner = this
         binding.editorViewModel = viewModel
-        viewModel.statementEditView.value = binding.edittextQueryEditor
+        viewModel.editTextStatement.value = binding.edittextQueryEditor
         binding.btnQueryEditorRun.setOnClickListener {
             val result = viewModel.execStatement()
             EditorUtils.renderResult(binding, result)

app/src/main/java/com/csapp/sqli/viewmodel/EditorViewModel.kt

@@ -1,39 +1,54 @@
 package com.csapp.sqli.viewmodel
 
+import android.text.Layout
 import android.widget.EditText
+import androidx.lifecycle.LiveData
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
 import com.csapp.sqli.model.LineNumber
 import com.csapp.sqli.repository.DatabaseRepository
 
 class EditorViewModel(private val databaseRepository: DatabaseRepository) : ViewModel() {
-    private val lineNumberModel = LineNumber("")
-    var statementEditView = MutableLiveData<EditText>()
-    val lineNumberView = MutableLiveData<String>()
+    private val modelLineNumber = LineNumber()
 
+    private val _editTextStatement = MutableLiveData<EditText>()
+    val editTextStatement: MutableLiveData<EditText> = _editTextStatement
+
+    private val _textViewLineNumber = MutableLiveData<String>()
+    val textViewLineNumber: LiveData<String> = _textViewLineNumber
+
+    // Data binding with Activity_editor.xml #afterTextChanged()
     fun onStatementChanged() {
-        val editText = statementEditView.value
-        val layout = editText?.layout
-        layout?.let {
-            lineNumberModel.content = generateLineNumber(it.lineCount)
-            lineNumberView.value = lineNumberModel.content
+        val editText = editTextStatement.value
+        editText?.layout?.let { updateLineNumbers(it) }
+    }
+
+    // If line number changed, update model and render line number text view
+    private fun updateLineNumbers(it: Layout) {
+        if (it.lineCount != modelLineNumber.number) {
+            modelLineNumber.content = generateLineNumber(it.lineCount)
+            modelLineNumber.number = it.lineCount
+            _textViewLineNumber.value = modelLineNumber.content
         }
     }
 
+    // View binding with Activity_editor.xml, Check Editor Activity
     fun execStatement(): Any? {
-        return statementEditView.value?.let {
-            if (isQueryStatement(statementEditView.value.toString())) {
+        return _editTextStatement.value?.let {
+            if (isQueryStatement(editTextStatement.value.toString())) {
                 databaseRepository.execQuery(it.text.toString())
             } else {
                 databaseRepository.execStatement(it.text.toString())
             }
         }
     }
 
+    // Check if a statement starts with "SELECT" ignore case
     private fun isQueryStatement(statement: String): Boolean {
-        return statement.startsWith("SELECT") or statement.startsWith("select")
+        return statement.startsWith("SELECT", ignoreCase = true)
     }
 
+    // Generate line number like ""1/n2/n3/n ... count"
     private fun generateLineNumber(count: Int): String {
         val stringBuilder = StringBuilder()
         for (i in 1..count) {

app/src/main/res/layout/activity_editor.xml

@@ -44,7 +44,7 @@
                     android:lineSpacingExtra="@dimen/x_small_padding"
                     android:minWidth="@dimen/large_padding"
                     android:paddingTop="@dimen/small_padding"
-                    android:text="@{editorViewModel.lineNumberView}"
+                    android:text="@{editorViewModel.textViewLineNumber}"
                     android:textColor="@color/annotation"
                     android:textSize="@dimen/medium_font_size" />