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在 使用Intent调用Android系统自身的相机功能 中，演示了如何使用 intent 调用内置的相机进行拍照。本文我们将演示如何使用 Camera2 API 完成拍照任务。对于想要定制相机的开发人员来说，理解 Camera2 API 是必须要掌握的。

声明权限

使用相机并保存拍摄的相片，需要在应用的 AndroidManifest.xml 加入权限声明相机和存储的权限:

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<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-feature android:name="android.hardware.camera2.full" />

构造界面

构造一个包含一个 TextureView 和两个 Button 的界面， TextrueView 用来显示相机镜头所拍摄到的画面。

activity_main.xml

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<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextureView
        android:id="@+id/tuwPhoto"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/linearLayout"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <LinearLayout
        android:id="@+id/linearLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent">

        <Button
            android:id="@+id/btnOpenCamera"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Open Camera" />

        <Button
            android:id="@+id/btnTakePhoto"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Take Photo" />
    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

构建一个TextrueView 的监听器

使用 SurfaceTextureListener 监听器来监听（响应）TexttrueView 状态变化的情况

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TextureView.SurfaceTextureListener textureListener = new TextureView.SurfaceTextureListener() {

    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
    }
    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
        return false;
    }

    @Override
    public void onSurfaceTextureUpdated(SurfaceTexture surface) {
    }
};

构建一个相机状态的回调接口类

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private final CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
    @Override
    public void onOpened(CameraDevice camera) {
        cameraDevice = camera;
        createCameraPreview();
    }

    @Override
    public void onDisconnected(CameraDevice camera) {
        cameraDevice.close();
    }

    @Override
    public void onError(CameraDevice camera, int error) {
        cameraDevice.close();
        cameraDevice = null;
    }
};

创建一个相机会话回调接口

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final CameraCaptureSession.CaptureCallback captureCallbackListener = new CameraCaptureSession.CaptureCallback() {
    @Override
    public void onCaptureCompleted(CameraCaptureSession session, CaptureRequest request, TotalCaptureResult result) {
        super.onCaptureCompleted(session, request, result);
        Toast.makeText(MainActivity.this, "Saved:" + file, Toast.LENGTH_LONG).show();
        createCameraPreview();
    }
};

在按钮事件中打开相机

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private void openCamera() {
    CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    Log.e(TAG, "Open camera...");
    try {
        cameraId = manager.getCameraIdList()[0];
        CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
        StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
        assert map != null;
        imageDimension = map.getOutputSizes(SurfaceTexture.class)[0];
        this.checkPermission();
        manager.openCamera(cameraId, stateCallback, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
    Log.e(TAG, "openCamera completed.");
}
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