4. Camera2前后摄像头切换
任务说明
实现一个基于Camera2 API的前后摄像头切换功能。用户点击切换按钮后，应用能够在前置与后置摄像头之间实时切换预览画面，并正确更新当前摄像头标识。本案例聚焦于Camera2的基本打开流程与切换逻辑，不涉及拍照、录像等扩展功能。
核心实现
// CameraSwitchActivity.java
public class CameraSwitchActivity extends AppCompatActivity {
private static final int REQUEST_CAMERA_PERMISSION = 200;
private AutoFitTextureView textureView;
private Button switchButton;
private TextView cameraIdText;
private String cameraId;
private CameraDevice cameraDevice;
private CameraCaptureSession captureSession;
private CaptureRequest.Builder previewRequestBuilder;
private ImageReader imageReader;
private HandlerThread backgroundThread;
private Handler backgroundHandler;
private final CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(@NonNull CameraDevice camera) {
cameraDevice = camera;
createCameraPreviewSession();
}
@Override
public void onDisconnected(@NonNull CameraDevice camera) {
cameraDevice.close();
cameraDevice = null;
}
@Override
public void onError(@NonNull CameraDevice camera, int error) {
cameraDevice.close();
cameraDevice = null;
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_camera_switch);
textureView = findViewById(R.id.texture_view);
switchButton = findViewById(R.id.btn_switch);
cameraIdText = findViewById(R.id.tv_camera_id);
// 默认使用后置摄像头
cameraId = CameraCharacteristics.LENS_FACING_BACK + "";
switchButton.setOnClickListener(v -> switchCamera());
}
@Override
protected void onResume() {
super.onResume();
startBackgroundThread();
if (textureView.isAvailable()) {
openCamera();
} else {
textureView.setSurfaceTextureListener(surfaceTextureListener);
}
}
@Override
protected void onPause() {
closeCamera();
stopBackgroundThread();
super.onPause();
}
private final TextureView.SurfaceTextureListener surfaceTextureListener =
new TextureView.SurfaceTextureListener() {
@Override
public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
openCamera();
}
@Override
public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
}
@Override
public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
return true;
}
@Override
public void onSurfaceTextureUpdated(SurfaceTexture surface) {
}
};
private void openCamera() {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
!= PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.CAMERA}, REQUEST_CAMERA_PERMISSION);
return;
}
CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
try {
// 根据cameraId字符串查找对应镜头方向
for (String id : manager.getCameraIdList()) {
CameraCharacteristics characteristics = manager.getCameraCharacteristics(id);
Integer facing = characteristics.get(CameraCharacteristics.LENS_FACING);
if (facing != null && facing.toString().equals(cameraId)) {
manager.openCamera(id, stateCallback, backgroundHandler);
cameraIdText.setText("当前摄像头: " + (facing == CameraCharacteristics.LENS_FACING_FRONT ? "前置" : "后置"));
return;
}
}
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void switchCamera() {
if (cameraDevice == null) return;
// 切换摄像头方向标识
if (cameraId.equals(CameraCharacteristics.LENS_FACING_BACK + "")) {
cameraId = CameraCharacteristics.LENS_FACING_FRONT + "";
} else {
cameraId = CameraCharacteristics.LENS_FACING_BACK + "";
}
// 关闭当前摄像头并重新打开
closeCamera();
openCamera();
}
private void createCameraPreviewSession() {
try {
SurfaceTexture texture = textureView.getSurfaceTexture();
texture.setDefaultBufferSize(1920, 1080);
Surface surface = new Surface(texture);
previewRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
previewRequestBuilder.addTarget(surface);
cameraDevice.createCaptureSession(Collections.singletonList(surface),
new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession session) {
if (cameraDevice == null) return;
captureSession = session;
previewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
try {
captureSession.setRepeatingRequest(previewRequestBuilder.build(), null, backgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession session) {
}
}, backgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void closeCamera() {
if (captureSession != null) {
captureSession.close();
captureSession = null;
}
if (cameraDevice != null) {
cameraDevice.close();
cameraDevice = null;
}
}
private void startBackgroundThread() {
backgroundThread = new HandlerThread("CameraBackground");
backgroundThread.start();
backgroundHandler = new Handler(backgroundThread.getLooper());
}
private void stopBackgroundThread() {
if (backgroundThread != null) {
backgroundThread.quitSafely();
try {
backgroundThread.join();
backgroundThread = null;
backgroundHandler = null;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}布局文件
<!-- activity_camera_switch.xml -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<AutoFitTextureView
android:id="@+id/texture_view"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:padding="16dp">
<TextView
android:id="@+id/tv_camera_id"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="当前摄像头: 后置"
android:textSize="16sp" />
<Button
android:id="@+id/btn_switch"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="切换摄像头" />
</LinearLayout>
</LinearLayout>Manifest配置
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" android:required="true" />验证方法
- 在Android设备（需具备前后摄像头）上安装并运行应用，授予相机权限。
- 观察初始预览画面，确认显示的是后置摄像头画面，界面文本显示“当前摄像头: 后置”。
- 点击“切换摄像头”按钮，观察预览画面是否切换为前置摄像头画面，文本同步更新为“当前摄像头: 前置”。
- 再次点击按钮，确认能切回后置摄像头。
- 连续快速点击切换按钮5次以上，确认无崩溃、无黑屏，每次切换后预览均能正常恢复。
判定标准：每次点击切换按钮后，预览画面在1秒内完成切换且画面内容与所选摄像头方向一致；界面文本始终与当前实际使用的摄像头匹配；整个过程中无应用崩溃或ANR。