Android应用手电筒切换异常：仅能打开无法关闭

问题根源 #

你推测的没错：isFlashlightOn初始值被硬设为false，注册TorchCallback后立刻调用toggleFlashlight()时，回调还没来得及获取并更新手电筒的真实初始状态。当手电筒本来处于开启状态时，!isFlashlightOn计算结果为true，调用setTorchMode后还是保持开启，自然无法完成关闭操作。

解决方案 #

不要依赖回调初始化状态，直接通过CameraManager的getTorchMode()方法获取手电筒的当前真实状态，再执行切换逻辑。这个方法从API 23开始可用，正好适配camera2框架的最低版本要求。

修改后的完整代码 #

import android.app.Activity;
import android.content.Context;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraManager;
import android.os.Bundle;
import android.widget.Toast;

public class FlashlightToggleActivity extends Activity {
    private CameraManager cameraManager;
    private String cameraId;
    private boolean isFlashlightOn = false;

    private final CameraManager.TorchCallback torchCallback = new CameraManager.TorchCallback() {
        @Override
        public void onTorchModeChanged(String cameraId, boolean enabled) {
            super.onTorchModeChanged(cameraId, enabled);
            isFlashlightOn = enabled;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            for (String id : cameraManager.getCameraIdList()) {
                if (cameraManager.getCameraCharacteristics(id).get(CameraCharacteristics.FLASH_INFO_AVAILABLE)) {
                    cameraId = id;
                    break;
                }
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }

        if (cameraId == null) {
            Toast.makeText(this, "当前设备不支持手电筒", Toast.LENGTH_SHORT).show();
            finish();
            return;
        }

        // 关键：先获取手电筒当前真实状态
        try {
            isFlashlightOn = cameraManager.getTorchMode(cameraId);
        } catch (CameraAccessException e) {
            Toast.makeText(this, "获取手电筒状态失败：" + e.getMessage(), Toast.LENGTH_SHORT).show();
            e.printStackTrace();
            finish();
            return;
        }

        cameraManager.registerTorchCallback(torchCallback, null);
        toggleFlashlight();
    }

    private void toggleFlashlight() {
        try {
            boolean newState = !isFlashlightOn;
            cameraManager.setTorchMode(cameraId, newState);
            Toast.makeText(this, newState ? "手电筒已开启" : "手电筒已关闭", Toast.LENGTH_SHORT).show();
        } catch (CameraAccessException e) {
            Toast.makeText(this, "切换手电筒状态失败：" + e.getMessage(), Toast.LENGTH_SHORT).show();
        } finally {
            finish();
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        cameraManager.unregisterTorchCallback(torchCallback);
    }
}

额外注意事项 #

• 确保在AndroidManifest.xml中添加必要权限：

  <!-- API 23及以上需要 -->
  <uses-permission android:name="android.permission.CAMERA" />
  <!-- API 26及以上可以更精准地申请 -->
  <uses-permission android:name="android.permission.CAMERA_FLASH" />
  <!-- 声明设备支持手电筒特性 -->
  <uses-feature android:name="android.hardware.camera.flash" android:required="false" />
  

• 对于Android 6.0+（API 23），需要动态申请CAMERA权限，否则会抛出权限异常。

内容的提问来源于stack exchange，提问作者Vlad