Android手电筒代码不起作用

Question

我创建了一个简单的项目来使用手电筒功能。从许多不同的地方（基本上都以相同的方式），我组装了以下代码，但手电筒不会打开（没有引发异常） - 但它适用于相机时我拍照：

Example code

Example code 2

Example Code 3

    @Override
    protected void onResume() {
        super.onResume();

        try {


            // check flashlight support
            hasFlash = getApplicationContext().getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);

            if (!hasFlash) {
                // device doesn't support flash
                // Show alert message and close the application
                AlertDialog alert = new AlertDialog.Builder(MainActivity.this).create();
                alert.setTitle("Error");
                alert.setMessage("Sorry, your device doesn't support flash light!");
                alert.setButton("OK", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {

                        finish();
                    }
                });
                alert.show();
                return;
            }

            text_off = (TextView) findViewById(R.id.text_off);
            text_off.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    finish();
                    return;
                }
            });


            getCamera();
            turnOnFlash();

        } catch (Exception e) {
            Log.e(this.getClass().getSimpleName(), "onResume Error: "+e.getMessage());
        }

    }

    @Override
    protected void onPause() {      
        super.onPause();

        turnOffFlash();

    }






    private void getCamera() {
        if (camera == null) {
            try {
                camera = Camera.open();
                params = camera.getParameters();
            } catch (RuntimeException e) {
                Log.e(this.getClass().getSimpleName(), "Camera Error. Failed to Open. Error: "+e.getMessage());
            }
        }   
    }

    @SuppressWarnings("deprecation")
    private void turnOnFlash() {

        try {
            Log.d(this.getClass().getSimpleName(), "turnOnFlash CHECKPOINT ");


            if (camera == null || params == null) {
                return;
            }


            params = camera.getParameters();
            params.setFlashMode(Parameters.FLASH_MODE_ON); 
            // ALSO TRIED: params.setFlashMode(Parameters.FLASH_MODE_TORCH); 
            camera.setParameters(params);
            camera.startPreview();
            isFlashOn = true;

            Log.d(this.getClass().getSimpleName(), "turnOnFlash CHECKPOINT EXIT");

        } catch (Exception e) {
            Log.e(this.getClass().getSimpleName(), "Camera Error. Failed to Open. Error: "+e.getMessage());
        }

    }


    @SuppressWarnings("deprecation")
    private void turnOffFlash() {

        try {

            Log.d(this.getClass().getSimpleName(), "turnOffFlash CHECKPOINT ");

            if (camera == null || params == null) {
                return;
            }

            params = camera.getParameters();
            params.setFlashMode(Parameters.FLASH_MODE_OFF);
            camera.setParameters(params);
            camera.stopPreview();
            camera.release();
            isFlashOn = false;

        } catch (Exception e) {
            Log.e(this.getClass().getSimpleName(), "Camera Error. Failed to Open. Error: "+e.getMessage());
        }

    }

在清单中：

<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />

为什么这段代码不能打开/关闭手电筒？

硬件：Nexus 5

操作系统：Android Marshmallow

Answer 1

我认为您缺少额外的一行代码，这是某些设备所需要的。到目前为止，我遇到的所有设备都需要这 3 行：

// will work on some devices
mCamera.setParameters(parameters);
// Needed for some devices.
mCamera.setPreviewTexture(new SurfaceTexture(0));
// Needed for some more devices.
mCamera.startPreview();

如果您添加一些虚拟SurfaceTexture 它应该可以工作。您还可以查看完整的代码示例here。

相机 api 因手机而异，而且这些手机的详细信息记录不充分。