本頁面由 Cloud Translation API 翻譯而成。

相機鏡頭和功能

注意：本頁面是指 Camera2 套件。除非應用程式需要 Camera2 的特定低階功能，否則建議使用 CameraX。CameraX 和 Camera2 均支援 Android 5.0 (API 級別 21) 以上版本。

許多新式 Android 裝置的正面、背面或雙邊都配備兩個以上的鏡頭。每個鏡頭都有獨特的功能，例如連拍拍攝、手動控製或動作追蹤。用於存款檢查的應用程式可能只會使用第一個後置鏡頭，社群媒體應用程式可能會預設為前置鏡頭，但讓使用者能選擇在所有可用的鏡頭之間切換。他們也記得自己所做的選擇。

本頁說明如何列出相機鏡頭及其功能，以便您可以在應用程式中決定在特定情況下要使用的鏡頭。下列程式碼片段會擷取所有相機的清單，並對這些相機進行疊代：

Kotlin

try {
    val cameraIdList = cameraManager.cameraIdList // may be empty

    // iterate over available camera devices
    for (cameraId in cameraIdList) {
        val characteristics = cameraManager.getCameraCharacteristics(cameraId)
        val cameraLensFacing = characteristics.get(CameraCharacteristics.LENS_FACING)
        val cameraCapabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)

        // check if the selected camera device supports basic features
        // ensures backward compatibility with the original Camera API
        val isBackwardCompatible = cameraCapabilities?.contains(
            CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
        ...
    }
} catch (e: CameraAccessException) {
    e.message?.let { Log.e(TAG, it) }
    ...
}

Java

try {
    String[] cameraIdList = cameraManager.getCameraIdList(); // may be empty

    // iterate over available camera devices
    for (String cameraId : cameraIdList) {
        CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraId);
        int cameraLensFacing = characteristics.get(CameraCharacteristics.LENS_FACING);
        int[] cameraCapabilities =
            characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES);

        // check if the selected camera device supports basic features
        // ensures backward compatibility with the original Camera API
        boolean isBackwardCompatible = false;
        for (int capability : cameraCapabilities) {
            if (capability == CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) {
                isBackwardCompatible = true;
                break;
            }
        }
        ...
    }
} catch (CameraAccessException e) {
    Log.e(TAG, e.getMessage());
    ...
}

變數 cameraLensFacing 用於說明相機相對於裝置螢幕的方向，且具有下列其中一個值：

如要進一步瞭解鏡頭面設定，請參閱 CameraCharacteristics.LENS_FACING。

上述程式碼範例的變數 cameraCapabilities 包含其他功能的相關資訊，包括相機能否產生標準影格做為輸出資料 (而非僅產生深度感應器資料)。您可以確認 CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE 是否為該相機列出的功能之一，該功能會以旗標的形式儲存在 isBackwardCompatible 中。

選擇合理的預設值

根據預設，建議您在應用程式中開啟特定相機 (如果有的話)。舉例來說，自拍應用程式可能會開啟前置鏡頭，而擴增實境應用程式可能會啟動後置鏡頭。以下函式會傳回面向指定方向的第一個鏡頭：

Kotlin

fun getFirstCameraIdFacing(cameraManager: CameraManager,
                           facing: Int = CameraMetadata.LENS_FACING_BACK): String? {
    try {
        // Get list of all compatible cameras
        val cameraIds = cameraManager.cameraIdList.filter {
            val characteristics = cameraManager.getCameraCharacteristics(it)
            val capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)
            capabilities?.contains(
                    CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
        }

        // Iterate over the list of cameras and return the first one matching desired
        // lens-facing configuration
        cameraIds.forEach {
            val characteristics = cameraManager.getCameraCharacteristics(it)
            if (characteristics.get(CameraCharacteristics.LENS_FACING) == facing) {
                return it
            }
        }

        // If no camera matched desired orientation, return the first one from the list
        return cameraIds.firstOrNull()
    } catch (e: CameraAccessException) {
        e.message?.let { Log.e(TAG, it) }
    }
}

Java

public String getFirstCameraIdFacing(CameraManager cameraManager, @Nullable Integer facing) {
    if (facing == null) facing = CameraMetadata.LENS_FACING_BACK;
    String cameraId = null;

    try {
        // Get a list of all compatible cameras
        String[] cameraIdList = cameraManager.getCameraIdList();

        // Iterate over the list of cameras and return the first one matching desired
        // lens-facing configuration and backward compatibility
        for (String id : cameraIdList) {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
            int[] capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES);
            for (int capability : capabilities) {
                if (capability == CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE
                        && characteristics.get(CameraCharacteristics.LENS_FACING).equals(facing)) {
                    cameraId = id;
                    break;
                }
            }
        }

        // If no camera matches the desired orientation, return the first one from the list
        cameraId = cameraIdList[0];
    } catch (CameraAccessException e) {
        Log.e(TAG, "getFirstCameraIdFacing: " + e.getMessage());
    }

    return cameraId;
}

啟用攝影機切換功能

許多相機應用程式可讓使用者選擇切換鏡頭：

許多裝置都具備多部面向相同方向的相機。部分客房甚至有外部 USB 攝影機。如要提供 UI 讓使用者切換不同鏡頭相機，請針對各種可能的鏡頭設定選擇第一個可用的相機。

雖然沒有可用於選取下一個相機的通用邏輯，但下列程式碼適用於大多數用途：

Kotlin

fun filterCompatibleCameras(cameraIds: Array<String>,
                            cameraManager: CameraManager): List<String> {
    return cameraIds.filter {
        val characteristics = cameraManager.getCameraCharacteristics(it)
        characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)?.contains(
                CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
    }
}

fun filterCameraIdsFacing(cameraIds: List<String>, cameraManager: CameraManager,
                          facing: Int): List<String> {
    return cameraIds.filter {
        val characteristics = cameraManager.getCameraCharacteristics(it)
        characteristics.get(CameraCharacteristics.LENS_FACING) == facing
    }
}

fun getNextCameraId(cameraManager: CameraManager, currCameraId: String? = null): String? {
    // Get all front, back and external cameras in 3 separate lists
    val cameraIds = filterCompatibleCameras(cameraManager.cameraIdList, cameraManager)
    val backCameras = filterCameraIdsFacing(
            cameraIds, cameraManager, CameraMetadata.LENS_FACING_BACK)
    val frontCameras = filterCameraIdsFacing(
            cameraIds, cameraManager, CameraMetadata.LENS_FACING_FRONT)
    val externalCameras = filterCameraIdsFacing(
            cameraIds, cameraManager, CameraMetadata.LENS_FACING_EXTERNAL)

    // The recommended order of iteration is: all external, first back, first front
    val allCameras = (externalCameras + listOf(
            backCameras.firstOrNull(), frontCameras.firstOrNull())).filterNotNull()

    // Get the index of the currently selected camera in the list
    val cameraIndex = allCameras.indexOf(currCameraId)

    // The selected camera may not be in the list, for example it could be an
    // external camera that has been removed by the user
    return if (cameraIndex == -1) {
        // Return the first camera from the list
        allCameras.getOrNull(0)
    } else {
        // Return the next camera from the list, wrap around if necessary
        allCameras.getOrNull((cameraIndex + 1) % allCameras.size)
    }
}

Java

public List<String> filterCompatibleCameras(CameraManager cameraManager, String[] cameraIds) {
    final List<String> compatibleCameras = new ArrayList<>();

    try {
        for (String id : cameraIds) {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
            int[] capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES);
            for (int capability : capabilities) {
                if (capability == CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) {
                    compatibleCameras.add(id);
                }
            }
        }
    } catch (CameraAccessException e) {
        Log.e(TAG, "filterCompatibleCameras: " + e.getMessage());
    }

    return compatibleCameras;
}

public List<String> filterCameraIdsFacing(CameraManager cameraManager, List<String> cameraIds, int lensFacing) {
    final List<String> compatibleCameras = new ArrayList<>();

    try {
        for (String id : cameraIds) {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
            if (characteristics.get(CameraCharacteristics.LENS_FACING) == lensFacing) {
                compatibleCameras.add(id);
            }
        }
    } catch (CameraAccessException e) {
        Log.e(TAG, "filterCameraIdsFacing: " + e.getMessage());
    }

    return compatibleCameras;
}

public String getNextCameraId(CameraManager cameraManager, @Nullable String currentCameraId) {
    String nextCameraId = null;

    try {
        // Get all front, back, and external cameras in 3 separate lists
        List<String> compatibleCameraIds = filterCompatibleCameras(cameraManager, cameraManager.getCameraIdList());
        List<String> backCameras = filterCameraIdsFacing(cameraManager, compatibleCameraIds, CameraMetadata.LENS_FACING_BACK);
        List<String> frontCameras = filterCameraIdsFacing(cameraManager, compatibleCameraIds, CameraMetadata.LENS_FACING_FRONT);
        List<String>externalCameras = filterCameraIdsFacing(cameraManager, compatibleCameraIds, CameraMetadata.LENS_FACING_EXTERNAL);

        // The recommended order of iteration is: all external, first back, first front
        List<String> allCameras = new ArrayList<>(externalCameras);
        if (!backCameras.isEmpty()) allCameras.add(backCameras.get(0));
        if (!frontCameras.isEmpty()) allCameras.add(frontCameras.get(0));

        // Get the index of the currently selected camera in the list
        int cameraIndex = allCameras.indexOf(currentCameraId);

        // The selected camera may not be in the list, for example it could be an
        // external camera that has been removed by the user
        if (cameraIndex == -1) {
            // Return the first camera from the list
            nextCameraId = !allCameras.isEmpty() ? allCameras.get(0) : null;
        else {
            if (!allCameras.isEmpty()) {
                // Return the next camera from the list, wrap around if necessary
                nextCameraId = allCameras.get((cameraIndex + 1) % allCameras.size());
            }
        }
    } catch (CameraAccessException e) {
        Log.e(TAG, "getNextCameraId: " + e.getMessage());
    }

    return nextCameraId;
}

這個程式碼適用於具有多項不同設定的大量裝置。如要進一步瞭解如何將極端案例納入考量，請參閱 CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_LOGICAL_MULTI_CAMERA。

建立相容的應用程式

如果應用程式仍使用已淘汰的 Camera API，Camera.getNumberOfCameras() 傳回的相機數量取決於原始設備製造商 (OEM) 的實作方式。如果系統中設有邏輯多相機，為維持應用程式的回溯相容性，這個方法只會為每個邏輯相機和基礎實體相機群組公開一個攝影機。使用 Camera2 API 查看所有相機。

如要進一步瞭解相機方向的背景資訊，請參閱 Camera.CameraInfo.orientation。

一般來說，請使用 Camera.getCameraInfo() API 查詢所有相機 orientation，並只向切換鏡頭的使用者顯示各個可用方向的相機。

整合所有裝置類型

請勿假設應用程式一律會在配備一或兩個相機的手持裝置上執行。請改為選擇最適合應用程式的相機。如果您不需要特定鏡頭，請選取第一組朝向所需方向的相機。如果已連接外部相機，您可以假設使用者將其做為預設攝影機。