java - 在 Android 上保持应用程序在后台运行

Question

我对 Android 编程非常陌生。我正在开发一个简单的应用程序:Android 版 FlashLight。

如果用户按下菜单按钮或锁定屏幕，我需要应用程序继续在后台运行。在用户按下停止灯的按钮之前，灯不应停止。

下面是我的代码:

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.hardware.Camera.Parameters;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ImageButton;

public class MainActivity
        extends Activity {
    ImageButton btnSwitch;
    private Camera camera;
    private boolean isFlashOn;
    private boolean hasFlash;
    Parameters params;
    MediaPlayer mp;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // flash switch button
        btnSwitch = (ImageButton) findViewById(R.id.btnSwitch);
        // First check if device is supporting flashlight or not
        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) {
                    // closing the application
                    finish();
                }
            });
            alert.show();
            return;
        }
        // get the camera
        getCamera();
        // displaying button image
        toggleButtonImage();
        // Switch button click event to toggle flash on/off
        btnSwitch.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(isFlashOn) {
                    // turn off flash
                    turnOffFlash();
                } else {
                    // turn on flash
                    turnOnFlash();
                }
            }
        });
    }

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

    // Turning On flash
    private void turnOnFlash() {
        if(!isFlashOn) {
            if(camera == null || params == null) {
                return;
            }
            params = camera.getParameters();
            params.setFlashMode(Parameters.FLASH_MODE_TORCH);
            camera.setParameters(params);
            camera.startPreview();
            isFlashOn = true;
            // changing button/switch image
            toggleButtonImage();
        }
    }

    // Turning Off flash
    private void turnOffFlash() {
        if(isFlashOn) {
            if(camera == null || params == null) {
                return;
            }
            params = camera.getParameters();
            params.setFlashMode(Parameters.FLASH_MODE_OFF);
            camera.setParameters(params);
            camera.stopPreview();
            isFlashOn = false;
            // changing button/switch image
            toggleButtonImage();
        }
    }

    /*
     * Toggle switch button images
     * changing image states to on / off
     * */
    private void toggleButtonImage() {
        if(isFlashOn) {
            btnSwitch.setImageResource(R.drawable.btn_switch_on);
        } else {
            btnSwitch.setImageResource(R.drawable.btn_switch_off);
        }
    }

    /*
 * Playing sound
 * will play button toggle sound on flash on / off
 * */
    private void playSound() {
        if(isFlashOn) {
            mp = MediaPlayer.create(MainActivity.this, R.raw.light_switch_off);
        } else {
            mp = MediaPlayer.create(MainActivity.this, R.raw.light_switch_on);
        }
        mp.setOnCompletionListener(new OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mp) {
                // TODO Auto-generated method stub
                mp.release();
            }
        });
        mp.start();
    }

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

    @Override
    protected void onPause() {
        super.onPause();
        // on pause turn off the flash
        turnOffFlash();
    }

    @Override
    protected void onRestart() {
        super.onRestart();
    }

    @Override
    protected void onResume() {
        super.onResume();
        // on resume turn on the flash
        if(hasFlash) {
            turnOnFlash();
        }
    }

    @Override
    protected void onStart() {
        super.onStart();
        // on starting the app get the camera params
        getCamera();
    }

    @Override
    protected void onStop() {
        super.onStop();
        // on stop release the camera
        if(camera != null) {
            camera.release();
            camera = null;
        }
    }
}

Answer 1

您正在 onPause 中关闭灯。当屏幕锁定或应用程序最小化时，将调用 onPause。如果您不希望发生这种情况，请不要在那里调用它。