アクティビティを開始できませんComponentInfo：java.lang.NullPointerException

カメラアプリケーションを開くボタンがあるアクティビティがあり、トリミングを試みます。しかし、私の活動は始まりさえしません。それはおそらくボタンに関するものであり、クラッシュはsetonclicklistenerの後に発生します。手伝ってもらえますか？

これが私のMainActivityCrop.javaです：

public class MainActivityCrop extends Activity {

    //keep track of camera capture intent
    final int CAMERA_CAPTURE = 1;
    //captured picture uri
    private Uri picUri;
    //keep track of cropping intent
    final int PIC_CROP = 2;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d("onResume: ", " BB");
        setContentView(R.layout.activity_main_activity_crop);
        Log.d("onResume: ", " CC");
        //retrieve a reference to the UI button
        Button captureBtn = (Button)findViewById(R.id.capture_btn);
        //handle button clicks
        Log.d("onResume: ", " DD");
        captureBtn.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                Log.d("onResume: ", " EE");
                    try {
                        Log.d("onResume: ", " FF");
                        //use standard intent to capture an image
                        Intent captureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                        //we will handle the returned data in onActivityResult
                        startActivityForResult(captureIntent, CAMERA_CAPTURE);
                    }
                    catch(ActivityNotFoundException anfe){
                        //display an error message
                        String errorMessage = "Whoops - your device doesn't support capturing images!";
                        Toast toast = Toast.makeText(null, errorMessage, Toast.LENGTH_SHORT);
                        toast.show();
                    }
            }
        });

        }

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (resultCode == RESULT_OK) {
            //user is returning from capturing an image using the camera
            if(requestCode == CAMERA_CAPTURE){
                //get the Uri for the captured image
                picUri = data.getData(); 
                //carry out the crop operation
                performCrop();
            }
            //user is returning from cropping the image
            else if(requestCode == PIC_CROP){
                //get the returned data
                Bundle extras = data.getExtras();
                //get the cropped bitmap
                Bitmap thePic = extras.getParcelable("data");
                //retrieve a reference to the ImageView
                ImageView picView = (ImageView)findViewById(R.id.picture);
                //display the returned cropped image
                picView.setImageBitmap(thePic);
            }
        }
    }

    private void performCrop(){
        try {
            //call the standard crop action intent (the user device may not support it)
            Intent cropIntent = new Intent("com.android.camera.action.CROP"); 
                //indicate image type and Uri
            cropIntent.setDataAndType(picUri, "image/*");
                //set crop properties
            cropIntent.putExtra("crop", "true");
                //indicate aspect of desired crop
            cropIntent.putExtra("aspectX", 1);
            cropIntent.putExtra("aspectY", 1);
                //indicate output X and Y
            cropIntent.putExtra("outputX", 256);
            cropIntent.putExtra("outputY", 256);
                //retrieve data on return
            cropIntent.putExtra("return-data", true);
                //start the activity - we handle returning in onActivityResult
            startActivityForResult(cropIntent, PIC_CROP);
        }
        catch(ActivityNotFoundException anfe){
            //display an error message
            String errorMessage = "Whoops - your device doesn't support the crop action!";
            Toast toast = Toast.makeText(this, errorMessage, Toast.LENGTH_SHORT);
            toast.show();
        }
    }

}

これが私のfragment_main_activity_crop.xmlです：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

<Button
    android:id="@+id/capture_btn"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/capture" />

<ImageView
    android:id="@+id/picture"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:contentDescription="@string/picture"
    android:layout_margin="5dp"

    />

</LinearLayout>

これらはlogcatスクリプトです：

06-03 16:44:26.710: E/AndroidRuntime(5036): FATAL EXCEPTION: main
06-03 16:44:26.710: E/AndroidRuntime(5036): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.croptry/com.example.croptry.MainActivityCrop}: java.lang.NullPointerException
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1978)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2003)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1169)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.os.Looper.loop(Looper.java:137)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.ActivityThread.main(ActivityThread.java:4446)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at java.lang.reflect.Method.invokeNative(Native Method)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at java.lang.reflect.Method.invoke(Method.java:511)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at dalvik.system.NativeStart.main(Native Method)
06-03 16:44:26.710: E/AndroidRuntime(5036): Caused by: java.lang.NullPointerException
06-03 16:44:26.710: E/AndroidRuntime(5036):     at com.example.croptry.MainActivityCrop.onCreate(MainActivityCrop.java:37)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.Activity.performCreate(Activity.java:4465)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-03 16:44:26.710: E/AndroidRuntime(5036):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1942)