Android 定位應用程式 - StackPenguin 部落格

這是一個練習定位權限的App，我將重要的部分記錄下來。

1
<uses-permission android:name="android.permission.INTERNET" />
2
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
3
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

1
<uses-permission android:name="android.permission.INTERNET" />
2
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
3
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

android.permission.INTERNET : 允許應用程式開啟網路連線
android.permission.ACCESS_COARSE_LOCATION : 允許應用程式存取使用粗略的位置
android.permission.ACCESS_FINE_LOCATION : 允許應用程式存取使用精確的位置

LocationUtils.kt

hasLocationPermission function 回傳一個 Boolean→ true 或 false，代表有沒有定位權限。

1
class LocationUtils(val context: Context) {
2
    private val _fusedLocationClient: FusedLocationProviderClient =
3
        LocationServices.getFusedLocationProviderClient(context)
4
<div></div>
5
    @SuppressLint("MissingPermission")
6
    fun requestLocationUpdates(viewModel: LocationViewModel) {
7
        val locationCallback = object : LocationCallback() {
8
            override fun onLocationResult(locationResult: LocationResult) {
9
                super.onLocationResult(locationResult)
10
                locationResult.lastLocation?.let {
11
                    val location = LocationData(latitude = it.latitude, longitude = it.longitude)
12
                    viewModel.updateLocation(location)
13
                }
14
            }
15
        }
16
        val locationRequest = LocationRequest.Builder(
17
            Priority.PRIORITY_HIGH_ACCURACY, 1000
18
        ).build()
19
        _fusedLocationClient.requestLocationUpdates(
20
            locationRequest,
21
            locationCallback,
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            Looper.getMainLooper()
23
        )
24
    }
25
<div></div>
26
    fun hasLocationPermission(context: Context): Boolean {
27
        return ContextCompat.checkSelfPermission(
28
            context,
29
            Manifest.permission.ACCESS_FINE_LOCATION
30
        ) == PackageManager.PERMISSION_GRANTED
31
                &&
32
                ContextCompat.checkSelfPermission(
33
                    context,
34
                    Manifest.permission.ACCESS_COARSE_LOCATION
35
                ) == PackageManager.PERMISSION_GRANTED
36
    }
37
<div></div>
38
    fun reverseGeocodeLocation(location: LocationData): String {
39
        // The Geocoder constructor expects a java.util.Locale
40
        val geocoder = Geocoder(context, Locale.getDefault())
41
        val coordinate = LatLng(location.latitude, location.longitude)
42
        val addresses: MutableList<Address>? =
43
            geocoder.getFromLocation(coordinate.latitude, coordinate.longitude, 1)
44
<div></div>
45
        return if (addresses?.isNotEmpty() == true) {
46
            addresses[0]?.getAddressLine(0) ?: "Address line not found"
47
        } else {
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            "Address not found"
49
        }
50
    }
51
}

1
class LocationUtils(val context: Context) {
2
    private val _fusedLocationClient: FusedLocationProviderClient =
3
        LocationServices.getFusedLocationProviderClient(context)
4

5
    @SuppressLint("MissingPermission")
6
    fun requestLocationUpdates(viewModel: LocationViewModel) {
7
        val locationCallback = object : LocationCallback() {
8
            override fun onLocationResult(locationResult: LocationResult) {
9
                super.onLocationResult(locationResult)
10
                locationResult.lastLocation?.let {
11
                    val location = LocationData(latitude = it.latitude, longitude = it.longitude)
12
                    viewModel.updateLocation(location)
13
                }
14
            }
15
        }
16
        val locationRequest = LocationRequest.Builder(
17
            Priority.PRIORITY_HIGH_ACCURACY, 1000
18
        ).build()
19
        _fusedLocationClient.requestLocationUpdates(
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            locationRequest,
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            locationCallback,
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            Looper.getMainLooper()
23
        )
24
    }
25

26
    fun hasLocationPermission(context: Context): Boolean {
27
        return ContextCompat.checkSelfPermission(
28
            context,
29
            Manifest.permission.ACCESS_FINE_LOCATION
30
        ) == PackageManager.PERMISSION_GRANTED
31
                &&
32
                ContextCompat.checkSelfPermission(
33
                    context,
34
                    Manifest.permission.ACCESS_COARSE_LOCATION
35
                ) == PackageManager.PERMISSION_GRANTED
36
    }
37

38
    fun reverseGeocodeLocation(location: LocationData): String {
39
        // The Geocoder constructor expects a java.util.Locale
40
        val geocoder = Geocoder(context, Locale.getDefault())
41
        val coordinate = LatLng(location.latitude, location.longitude)
42
        val addresses: MutableList<Address>? =
43
            geocoder.getFromLocation(coordinate.latitude, coordinate.longitude, 1)
44

45
        return if (addresses?.isNotEmpty() == true) {
46
            addresses[0]?.getAddressLine(0) ?: "Address line not found"
47
        } else {
48
            "Address not found"
49
        }
50
    }
51
}

1
private val _fusedLocationClient: FusedLocationProviderClient =
2
    LocationServices.getFusedLocationProviderClient(context)

1
private val _fusedLocationClient: FusedLocationProviderClient =
2
    LocationServices.getFusedLocationProviderClient(context)

這是 Google 提供的 Fused Location Provider API，能整合 GPS、Wi-Fi、藍牙與行動網路的定位來源，讓定位更準確且省電。_fusedLocationClient 用來執行「請求位置更新」、「停止更新」、「取得最後位置」等操作。

requestLocationUpdates

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@SuppressLint("MissingPermission")
2
fun requestLocationUpdates(viewModel: LocationViewModel) {

1
@SuppressLint("MissingPermission")
2
fun requestLocationUpdates(viewModel: LocationViewModel) {

⚠️ 注意：這裡用了 @SuppressLint("MissingPermission")，代表你必須在呼叫這個函式前，確認已取得權限（也就是前面 LocationDisplay 檢查的部分）。

意思是保證外層一定會先檢查 hasLocationPermission() 才會進來，所以不用再提醒我 MissingPermission。

這個函式會每秒更新一次位置（因為下面設定了 1000 毫秒），然後將新位置傳給你的 LocationViewModel。

1
val locationCallback = object : LocationCallback() {
2
    override fun onLocationResult(locationResult: LocationResult) {
3
        super.onLocationResult(locationResult)
4
        locationResult.lastLocation?.let {
5
            val location = LocationData(latitude = it.latitude, longitude = it.longitude)
6
            viewModel.updateLocation(location)
7
        }
8
    }
9
}

1
val locationCallback = object : LocationCallback() {
2
    override fun onLocationResult(locationResult: LocationResult) {
3
        super.onLocationResult(locationResult)
4
        locationResult.lastLocation?.let {
5
            val location = LocationData(latitude = it.latitude, longitude = it.longitude)
6
            viewModel.updateLocation(location)
7
        }
8
    }
9
}

當系統取得新的定位資訊時，會呼叫 onLocationResult。

lastLocation 是最新的 Location 物件（包含緯度與經度）。

1
package com.example.locationapp
2
<div></div>
3
data class LocationData(
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    val latitude: Double,
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    val longitude: Double
6
)

1
package com.example.locationapp
2

3
data class LocationData(
4
    val latitude: Double,
5
    val longitude: Double
6
)

LocationData 是我們定義的資料類別，用來包裝座標。

呼叫 viewModel.updateLocation(location) → 把資料傳給 ViewModel 更新 UI。

1
_fusedLocationClient.requestLocationUpdates(
2
    locationRequest,
3
    locationCallback,
4
    Looper.getMainLooper()
5
)

1
_fusedLocationClient.requestLocationUpdates(
2
    locationRequest,
3
    locationCallback,
4
    Looper.getMainLooper()
5
)

這行讓 app 持續監聽位置變化。

hasLocationPermission

LocationUtils 要持有 Context，才能呼叫系統 API（如 ContextCompat.checkSelfPermission）來檢查權限。

return 這段是重點：ContextCompat.checkSelfPermission() 是Android官方提供的工具，用來檢查 App 是否擁有某個權限。它會回傳一個整數值（PERMISSION_GRANTED 或 PERMISSION_DENIED）。

這段程式碼的功能就像是你在檢查一個房間的門：

「門有沒有上鎖？如果鎖是開著的，就代表我可以進去。」
ContextCompat (檢查員)： 你可以把它想像成 Android 系統中的一位通用檢查員或萬用工具箱。它的工作就是確保你的程式碼在所有不同型號和版本的 Android 手機上都能正常運作（這就是 Compat 兼容性的意思）。
.checkSelfPermission() (檢查方法)： 這是檢查員專門用來檢查特定權限狀態的方法。

參數一 (context)： 告訴檢查員「在哪個應用程式環境」下進行檢查。

參數二 (Manifest.permission.ACCESS_FINE_LOCATION)： 告訴檢查員「要檢查哪一種權限」。

為什麼需要 `ContextCompat.checkSelfPermission()`？

我們不直接使用 PackageManager.PERMISSION_GRANTED 進行判斷，是因為 PackageManager.PERMISSION_GRANTED 只是一個「結果代碼」（密碼），而 ContextCompat.checkSelfPermission() 才是「執行檢查的動作」。

reverseGeocodeLocation

1
fun reverseGeocodeLocation(location: LocationData): String {
2
    val geocoder = Geocoder(context, Locale.getDefault())
3
    val coordinate = LatLng(location.latitude, location.longitude)
4
    val addresses: MutableList<Address>? =
5
        geocoder.getFromLocation(coordinate.latitude, coordinate.longitude, 1)

1
fun reverseGeocodeLocation(location: LocationData): String {
2
    val geocoder = Geocoder(context, Locale.getDefault())
3
    val coordinate = LatLng(location.latitude, location.longitude)
4
    val addresses: MutableList<Address>? =
5
        geocoder.getFromLocation(coordinate.latitude, coordinate.longitude, 1)

用 Geocoder 根據經緯度查詢地點名稱。getFromLocation() 會回傳一個地址列表（可能含國家、城市、街道）。

MainActivity.kt

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@Composable
2
fun MyApp(modifier: Modifier) {
3
    val context = LocalContext.current
4
    val locationUtils = LocationUtils(context)
5
    LocationDisplay(locationUtils = locationUtils, context = context)
6
}

1
@Composable
2
fun MyApp(modifier: Modifier) {
3
    val context = LocalContext.current
4
    val locationUtils = LocationUtils(context)
5
    LocationDisplay(locationUtils = locationUtils, context = context)
6
}

1
class MainActivity : ComponentActivity() {
2
    override fun onCreate(savedInstanceState: Bundle?) {
3
        super.onCreate(savedInstanceState)
4
        enableEdgeToEdge()
5
        setContent {
6
            val viewModel: LocationViewModel = viewModel()
7
            LocationAppTheme {
8
                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
9
                    MyApp(viewModel = viewModel,modifier = Modifier.padding(innerPadding))
10
                }
11
            }
12
        }
13
    }
14
}

1
class MainActivity : ComponentActivity() {
2
    override fun onCreate(savedInstanceState: Bundle?) {
3
        super.onCreate(savedInstanceState)
4
        enableEdgeToEdge()
5
        setContent {
6
            val viewModel: LocationViewModel = viewModel()
7
            LocationAppTheme {
8
                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
9
                    MyApp(viewModel = viewModel,modifier = Modifier.padding(innerPadding))
10
                }
11
            }
12
        }
13
    }
14
}

Context： 是一個核心的 Android 系統類別，它提供了應用程式全域資訊，例如資源、資料庫、文件系統路徑，以及存取系統服務（如定位服務）的管道。

LocalContext.current： 這是 Jetpack Compose 框架提供的一個 CompositionLocal。它用於在可組合函數中存取 Android 應用程式的 Context 物件。

LocationDisplay(locationUtils = locationUtils, context = context) 這行程式碼的作用是調用一個名為 LocationDisplay 的 Compose UI 元件，向它傳遞所需的資料和環境依賴。

1
@Composable
2
fun LocationDisplay(
3
    locationUtils: LocationUtils,
4
    viewModel: LocationViewModel,
5
    context: Context
6
) {
7
    val location = viewModel.location.value
8

9
    val address = location?.let {
10
        locationUtils.reverseGeocodeLocation(location)
11
    }
12
<div></div>
13
    val requestPermissionLauncher = rememberLauncherForActivityResult(
14
        contract = ActivityResultContracts.RequestMultiplePermissions(),
15
        onResult = { permissions ->
16
            if (permissions[Manifest.permission.ACCESS_COARSE_LOCATION] == true
17
                && permissions[Manifest.permission.ACCESS_FINE_LOCATION] == true
18
            ) {
19
                // 擁有 location 權限
20
                locationUtils.requestLocationUpdates(viewModel = viewModel)
21
<div></div>
22
            } else {
23
                // 要求權限
24
                val rationaleRequired = ActivityCompat.shouldShowRequestPermissionRationale(
25
                    context as MainActivity,
26
                    Manifest.permission.ACCESS_FINE_LOCATION
27
                ) || ActivityCompat.shouldShowRequestPermissionRationale(
28
                    context as MainActivity,
29
                    Manifest.permission.ACCESS_COARSE_LOCATION
30
                )
31
<div></div>
32
                if (rationaleRequired) {
33
                    Toast.makeText(
34
                        context,
35
                        "Location Permission is required for this feature to work",
36
                        Toast.LENGTH_LONG
37
                    ).show()
38
                } else {
39
                    Toast.makeText(
40
                        context,
41
                        "Location Permission is required, Please enable from settings",
42
                        Toast.LENGTH_LONG
43
                    ).show()
44
                }
45
            }
46
        }
47
    )
48
<div></div>
49
    Column(
50
        modifier = Modifier.fillMaxSize(),
51
        horizontalAlignment = Alignment.CenterHorizontally,
52
        verticalArrangement = Arrangement.Center
53
    ) {
54
        if(location != null) {
55
            Text("Address: ${location.latitude} ${location.longitude} \n $address ")
56
        }
57
        Text(text = "Location not available")
58
<div></div>
59
        Button(onClick = {
60
            if (locationUtils.hasLocationPermission(context)) {
61
                locationUtils.requestLocationUpdates(viewModel)
62
            } else {
63
                requestPermissionLauncher.launch(
64
                    arrayOf(
65
                        Manifest.permission.ACCESS_FINE_LOCATION,
66
                        Manifest.permission.ACCESS_COARSE_LOCATION
67
                    )
68
                )
69
            }
70
        }) {
71
            Text(text = "Get Location")
72
        }
73
    }
74
}

1
@Composable
2
fun LocationDisplay(
3
    locationUtils: LocationUtils,
4
    viewModel: LocationViewModel,
5
    context: Context
6
) {
7
    val location = viewModel.location.value
8

9
    val address = location?.let {
10
        locationUtils.reverseGeocodeLocation(location)
11
    }
12

13
    val requestPermissionLauncher = rememberLauncherForActivityResult(
14
        contract = ActivityResultContracts.RequestMultiplePermissions(),
15
        onResult = { permissions ->
16
            if (permissions[Manifest.permission.ACCESS_COARSE_LOCATION] == true
17
                && permissions[Manifest.permission.ACCESS_FINE_LOCATION] == true
18
            ) {
19
                // 擁有 location 權限
20
                locationUtils.requestLocationUpdates(viewModel = viewModel)
21

22
            } else {
23
                // 要求權限
24
                val rationaleRequired = ActivityCompat.shouldShowRequestPermissionRationale(
25
                    context as MainActivity,
26
                    Manifest.permission.ACCESS_FINE_LOCATION
27
                ) || ActivityCompat.shouldShowRequestPermissionRationale(
28
                    context as MainActivity,
29
                    Manifest.permission.ACCESS_COARSE_LOCATION
30
                )
31

32
                if (rationaleRequired) {
33
                    Toast.makeText(
34
                        context,
35
                        "Location Permission is required for this feature to work",
36
                        Toast.LENGTH_LONG
37
                    ).show()
38
                } else {
39
                    Toast.makeText(
40
                        context,
41
                        "Location Permission is required, Please enable from settings",
42
                        Toast.LENGTH_LONG
43
                    ).show()
44
                }
45
            }
46
        }
47
    )
48

49
    Column(
50
        modifier = Modifier.fillMaxSize(),
51
        horizontalAlignment = Alignment.CenterHorizontally,
52
        verticalArrangement = Arrangement.Center
53
    ) {
54
        if(location != null) {
55
            Text("Address: ${location.latitude} ${location.longitude} \n $address ")
56
        }
57
        Text(text = "Location not available")
58

59
        Button(onClick = {
60
            if (locationUtils.hasLocationPermission(context)) {
61
                locationUtils.requestLocationUpdates(viewModel)
62
            } else {
63
                requestPermissionLauncher.launch(
64
                    arrayOf(
65
                        Manifest.permission.ACCESS_FINE_LOCATION,
66
                        Manifest.permission.ACCESS_COARSE_LOCATION
67
                    )
68
                )
69
            }
70
        }) {
71
            Text(text = "Get Location")
72
        }
73
    }
74
}

主要公能：顯示一個文字 + 按鈕，並處理按下按鈕後檢查或請求定位權限。

contract = ActivityResultContracts.RequestMultiplePermissions()

表示這個 launcher 可以一次請求多個權限（這裡是 coarse + fine）。

onResult = { permissions -> ... }

系統對話框關閉後，會回傳使用者是否授權。

1
if (permissions[Manifest.permission.ACCESS_COARSE_LOCATION] == true
2
    && permissions[Manifest.permission.ACCESS_FINE_LOCATION] == true
3
) {
4
    // 已擁有定位權限
5
} else {
6
    // 尚未取得權限，顯示提示
7
}

1
if (permissions[Manifest.permission.ACCESS_COARSE_LOCATION] == true
2
    && permissions[Manifest.permission.ACCESS_FINE_LOCATION] == true
3
) {
4
    // 已擁有定位權限
5
} else {
6
    // 尚未取得權限，顯示提示
7
}

若兩個權限都有允許，目前就什麼都不做；否則，進入「沒有權限」的分支。

如果沒權限 → 顯示提示 Toast

1
val rationaleRequired = ActivityCompat.shouldShowRequestPermissionRationale(
2
    context as MainActivity,
3
    Manifest.permission.ACCESS_FINE_LOCATION
4
) || ActivityCompat.shouldShowRequestPermissionRationale(
5
    context as MainActivity,
6
    Manifest.permission.ACCESS_COARSE_LOCATION
7
)

1
val rationaleRequired = ActivityCompat.shouldShowRequestPermissionRationale(
2
    context as MainActivity,
3
    Manifest.permission.ACCESS_FINE_LOCATION
4
) || ActivityCompat.shouldShowRequestPermissionRationale(
5
    context as MainActivity,
6
    Manifest.permission.ACCESS_COARSE_LOCATION
7
)

shouldShowRequestPermissionRationale(…)

這是 Android 的 API，用來判斷：

使用者曾拒絕過權限（但沒勾「不再詢問」 → 回傳 true
使用者勾了「不再詢問」或第一次詢問 → 回傳 false

1
if (rationaleRequired) {
2
    Toast.makeText(context, "Location Permission is required for this feature to work", Toast.LENGTH_LONG).show()
3
} else {
4
    Toast.makeText(context, "Location Permission is required, Please enable from settings", Toast.LENGTH_LONG).show()
5
}

1
if (rationaleRequired) {
2
    Toast.makeText(context, "Location Permission is required for this feature to work", Toast.LENGTH_LONG).show()
3
} else {
4
    Toast.makeText(context, "Location Permission is required, Please enable from settings", Toast.LENGTH_LONG).show()
5
}

LocationViewModel.kt

1
package com.example.locationapp
2
<div></div>
3
import androidx.compose.runtime.State
4
import androidx.compose.runtime.mutableStateOf
5
import androidx.lifecycle.ViewModel
6
<div></div>
7
class LocationViewModel: ViewModel() {
8
    private val _location = mutableStateOf<LocationData?>(null)
9
    val location: State<LocationData?> = _location
10
<div></div>
11
    fun updateLocation(newLocation: LocationData) {
12
        _location.value = newLocation
13
    }
14
<div></div>
15
}

1
package com.example.locationapp
2

3
import androidx.compose.runtime.State
4
import androidx.compose.runtime.mutableStateOf
5
import androidx.lifecycle.ViewModel
6

7
class LocationViewModel: ViewModel() {
8
    private val _location = mutableStateOf<LocationData?>(null)
9
    val location: State<LocationData?> = _location
10

11
    fun updateLocation(newLocation: LocationData) {
12
        _location.value = newLocation
13
    }
14

15
}

1
private val _location = mutableStateOf<LocationData?>(null)

1
private val _location = mutableStateOf<LocationData?>(null)

mutableStateOf 它包裝了一個變數，當值改變時，Compose UI 會自動重新組合（recompose）。

LocationData? → 泛型裡面的 ? 代表可以是 null，表示「可能還沒取得位置」。

_location 是私有的可變，location 是公開的唯讀。

1
fun updateLocation(newLocation: LocationData) {
2
    _location.value = newLocation
3
}

1
fun updateLocation(newLocation: LocationData) {
2
    _location.value = newLocation
3
}

當 LocationUtils 拿到新座標後，會呼叫updateLocation更新座標。

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