Мобильная версияI'm working through Android Developers online tutorial for 1st Android apps.
I have a C coding background, but very limited object-oriented experience.
I am trying to sort out what's going on when I call a method with "modifier." vs "Modifier.". I assume the lowercase version calls the method on the object passed to it, whereas the uppercase version is somehow a new object local to the child that called it as a parameter. The lowercase version seems to affect previous methods applied to that "parent". Here's an example of both, with observed behavior. The only difference between the 2 examples is the case (uppercase vs lowercase) of "m" in that "modifier" call in the first Text() call.
The first example is desired behavior. In the first "Text" call, I use "Modifier"(uppercase). This preserves the centered vertical arrangement of the parent column. ("OneQuadrant" function is called 4 times, image below shows the preview pane)
@Composable fun OneQuadrant(title: String, info: String, bColor: Color, modifier: Modifier) { Column ( horizontalAlignment = Alignment.CenterHorizontally, verticalArrangement = Arrangement.Center, modifier = modifier .fillMaxHeight() .background(bColor) .padding(16.dp) ) { Text( text = title, fontWeight = Bold, modifier = Modifier.padding(bottom=16.dp) ) Text( text = info, textAlign = TextAlign.Justify, ) } } The 2nd example is undesired behavior. The first "Text" call uses "modifier" (lowercase). This evidently overrides the centered vertical arrangement in the parent column.
@Composable fun OneQuadrant(title: String, info: String, bColor: Color, modifier: Modifier) { Column ( horizontalAlignment = Alignment.CenterHorizontally, verticalArrangement = Arrangement.Center, modifier = modifier .fillMaxHeight() .background(bColor) .padding(16.dp) ) { Text( text = title, fontWeight = Bold, modifier = modifier.padding(bottom=16.dp) ) Text( text = info, textAlign = TextAlign.Justify, ) } } Q1: In the 2nd example, even if the lowercase version is acting on the parent, why would that undo the centered vertical arrangement? I see that bottom padding and centered are inconsistent, and probably the last call prevails. However, the Column also calls for padding after the Arrangement.Center statement, and that works OK.
Q2: If it is mapping back to the parent, why isn't the call within "Column" also mapping back to its parent, since it was passed as a parameter?
Q3: What is the right mental model here, to understand what's going on? I think I'm confused in part by what the underlying objects are. The composable functions have names that suggest objects, but they are really functions acting on some other object(s)... true?
I did read up on Kotlin "companion objects", but that didn't really help. I'm guessing this is somehow related to pass-by-reference behavior in Kotlin, but I cannot figure it out. Can you please explain, or refer me to a clear reference? Thank you!
In case it is useful, here is the function that calls OneQuadrant 4 times.
fun DisplayQuadrants(modifier: Modifier = Modifier) { Column (modifier.fillMaxWidth()) { Row (modifier.weight(1f)){ OneQuadrant( title = stringResource(R.string.text_composable), info = stringResource(R.string.displays_text), bColor = Color(0xFFEADDFF), modifier = modifier.weight(1f) ) OneQuadrant( title = stringResource(R.string.image_composable), info = stringResource(R.string.creates_composable), bColor = Color(0xFFD0BCFF), modifier = modifier.weight(1f) ) } Row (modifier.weight(1f)){ OneQuadrant ( title = stringResource(R.string.row_composable), info = stringResource(R.string.a_layout), bColor = Color(0xFFD0BCFF), modifier = modifier.weight(1f) ) OneQuadrant( title = stringResource(R.string.column_composable), info = stringResource(R.string.vertical), bColor = Color(0xFFF6EDFF), modifier = modifier.weight(1f) ) } } } This "DisplayQuadrants" is called in MainActivity as follows:
class MainActivity : ComponentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContent { QuadrantsTheme { // A surface container using the 'background' color from the theme Surface( modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background ) { DisplayQuadrants(modifier = Modifier) } } } } }
Источник: https://stackoverflow.com/questions/780 ... ior-explan
