android手電筒第二次啓動錯誤

Question

我試圖做一個非常基本的手電筒應用程序。當用戶打開應用程序時，沒有佈局將被誇大，手電筒將打開。一旦用戶第二次打開手電筒將關閉。看起來好像打開手電筒並不麻煩，但在應用程序第二次啓動時將其關閉，這就是我有點不確定的地方。我不斷收到此錯誤：

Process: com.example.rifatrashid.lighter, PID: 16558 
     java.lang.RuntimeException: Unable to resume activity  {com.example.rifatrashid.lighter/com.example.rifatrashid.lighter.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera$Parameters.setFlashMode(java.lang.String)' on a null object reference 
     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2951) 
     at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2982) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2365) 
     at android.app.ActivityThread.access$800(ActivityThread.java:144) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:135) 
     at android.app.ActivityThread.main(ActivityThread.java:5221) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera$Parameters.setFlashMode(java.lang.String)' on a null object reference 
     at com.example.rifatrashid.lighter.MainActivity.onResume(MainActivity.java:33) 
     at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1241) 
     at android.app.Activity.performResume(Activity.java:6019) 
     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2940) 

public class MainActivity extends Activity { 
private boolean haslight; 
private Integer val = 0; 
private Camera camera; 
private Camera.Parameters parameters; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
haslight = getApplicationContext().getPackageManager().hasSystemFeature((PackageManager.FEATURE_CAMERA_FLASH)); 
if(!haslight) { 

} 
camera = Camera.open(); 
parameters = camera.getParameters(); 
val++; 
if(val>1) 
    val=0; 
switch (val){ 
    case 1: 
     parameters.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH); 
     camera.setParameters(parameters); 
     camera.startPreview(); 
     break; 
    case 0: 
     camera.stopPreview(); 
     camera.release(); 
     break; 
} 
} 
} 

Answer 1

堆棧跟蹤說你試圖調用一個空對象引用setFlashMode。在使用之前，您需要檢查參數是否爲空：

if (parameters != null) 
    parameters.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);