相機鏡頭和功能

注意：本頁面所述是指 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。

許多新型 Android 裝置的前置、後或鏡頭都配備兩個以上的相機 兩側每個鏡頭都有獨特功能，例如連拍 手動控製或動作追蹤存入支票的應用程式可能只能使用 第一種後置鏡頭，社群媒體應用程式則可能預設使用 前置鏡頭，但提供使用者切換可用選項 鏡頭。裝置也能記住孩子的選擇。

本頁說明如何列出相機鏡頭及其功能，以便您 就能在應用程式中決定要採用哪種鏡頭。 下列程式碼片段會擷取所有相機的清單，並反覆進行疊代 他們可以：

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());
    ...
}

cameraLensFacing 變數用於說明相機面對的方向 ，且具有下列其中一個值：

• CameraMetadata.LENS_FACING_FRONT
• CameraMetadata.LENS_FACING_BACK
• CameraMetadata.LENS_FACING_EXTERNAL

如要進一步瞭解鏡頭方向設定，請參閱 CameraCharacteristics.LENS_FACING。

上述程式碼範例中的 cameraCapabilities 變數包含 其他功能的資訊，包括相機是否 能產生標準影格做為輸出內容 (相對於只有 深度感應器資料)。您可以檢查 CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE敬上 是相機列出的其中一項功能，會在 isBackwardCompatible。

選擇合理的預設值

您可能會想在應用程式中預設開啟特定攝影機 (如果有的話)。舉例來說，自拍應用程式可能會以前置鏡頭開啟 而擴增實境應用程式則可能是以後置鏡頭啟動。 下方函式會傳回第一個面對指定方向的鏡頭：

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;
}

啟用切換鏡頭

許多相機應用程式都為使用者提供切換鏡頭的選項：

圖 1 Google 相機應用程式的切換鏡頭按鈕

許多裝置都有多台鏡頭朝向相同方向的鏡頭。有些甚至有 外部 USB 攝影機。為提供使用者介面，方便使用者切換 為相機選擇第一個可用的鏡頭 。

雖然沒有通用的邏輯可以選取下一部鏡頭， 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;
}

這個代碼適用於多種裝置，且有多種不同的 儲存空間設定如要進一步瞭解如何將極端情況納入考量，請參閱「CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_LOGICAL_MULTI_CAMERA」。

建立相容的應用程式

如果應用程式仍在使用已淘汰的 Camera API，則相機數量 並 Camera.getNumberOfCameras()敬上 會傳回 取決於原始設備製造商 (OEM) 實作。如果 為維持應用程式回溯相容性，此方法僅會公開一個 。 使用 Camera2 API 查看所有相機。

如需更多相機方向的背景資訊，請參見 Camera.CameraInfo.orientation。

一般來說，請使用 Camera.getCameraInfo()敬上 用於查詢所有相機的 API orientation， 並且只向符合以下條件的使用者顯示一部相機 切換鏡頭。

適用於所有裝置類型

請勿假設應用程式一律會在手持裝置上， 連接兩部攝影機請改為為應用程式選擇最合適的相機。如果發生以下情況： 不需要特定攝影機，請選取第一個面向所需的鏡頭 往上移動即可如果連接外接式攝影機，您可能會誤以為使用者 請用預設值將其清除。