java.lang.RuntimeException:无法启动活动组件信息照相机照片上载

在运行android应用程序进行相机照片上传时，我遇到了null点异常。下面可能是get action bar return null。如果我的猜测是正确的，那么我应该添加一个空检查

下面是原木猫

`12-28 16:41:15.290    2047-2047/info.androidhive.camerafileupload E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: info.androidhive.camerafileupload, PID: 2047
java.lang.RuntimeException: Unable to start activity   ComponentInfo{info.androidhive.camerafileupload/info.androidhive.camerafileupload.MainActivity}:     java.lang.NullPointerException: Attempt to invoke virtual method 'void  android.app.ActionBar.setBackgroundDrawable(android.graphics.drawable.Drawable)' on a null object  reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
        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:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method void android.app.ActionBar.setBackgroundDrawable(android.graphics.drawable.Drawable) on a null object reference
        at info.androidhive.camerafileupload.MainActivity.onCreate(MainActivity.java:46)
        at android.app.Activity.performCreate(Activity.java:5933)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
        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:899)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)`

下面是我的mainactivity.java

package info.androidhive.camerafileupload;

import java.io.File;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

import android.app.Activity;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity {

// LogCat tag
private static final String TAG = MainActivity.class.getSimpleName();


// Camera activity request codes
private static final int CAMERA_CAPTURE_IMAGE_REQUEST_CODE = 100;
private static final int CAMERA_CAPTURE_VIDEO_REQUEST_CODE = 200;

public static final int MEDIA_TYPE_IMAGE = 1;
public static final int MEDIA_TYPE_VIDEO = 2;

private Uri fileUri; // file url to store image/video

private Button btnCapturePicture, btnRecordVideo;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    // Changing action bar background color
    // These two lines are not needed
    getActionBar().setBackgroundDrawable(new     ColorDrawable(Color.parseColor(getResources().getString(R.color.action_bar))));

    btnCapturePicture = (Button) findViewById(R.id.btnCapturePicture);
    btnRecordVideo = (Button) findViewById(R.id.btnRecordVideo);

    /**
     * Capture image button click event
     */
    btnCapturePicture.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // capture picture
            captureImage();
        }
    });

    /**
     * Record video button click event
     */
    btnRecordVideo.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // record video
            recordVideo();
        }
    });

    // Checking camera availability
    if (!isDeviceSupportCamera()) {
        Toast.makeText(getApplicationContext(),
                "Sorry! Your device doesn't support camera",
                Toast.LENGTH_LONG).show();
        // will close the app if the device does't have camera
        finish();
    }
}

/**
 * Checking device has camera hardware or not
 * */
private boolean isDeviceSupportCamera() {
    if (getApplicationContext().getPackageManager().hasSystemFeature(
            PackageManager.FEATURE_CAMERA)) {
        // this device has a camera
        return true;
    } else {
        // no camera on this device
        return false;
    }
}

/**
 * Launching camera app to capture image
 */
private void captureImage() {
    Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

    fileUri = getOutputMediaFileUri(MEDIA_TYPE_IMAGE);

    intent.putExtra(MediaStore.EXTRA_OUTPUT, fileUri);

    // start the image capture Intent
    startActivityForResult(intent, CAMERA_CAPTURE_IMAGE_REQUEST_CODE);
}

/**
 * Launching camera app to record video
 */
private void recordVideo() {
    Intent intent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);

    fileUri = getOutputMediaFileUri(MEDIA_TYPE_VIDEO);

    // set video quality
    intent.putExtra(MediaStore.EXTRA_VIDEO_QUALITY, 1);

    intent.putExtra(MediaStore.EXTRA_OUTPUT, fileUri); // set the image file
    // name

    // start the video capture Intent
    startActivityForResult(intent, CAMERA_CAPTURE_VIDEO_REQUEST_CODE);
}

/**
 * Here we store the file url as it will be null after returning from camera
 * app
 */
@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    // save file url in bundle as it will be null on screen orientation
    // changes
    outState.putParcelable("file_uri", fileUri);
}

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

    // get the file url
    fileUri = savedInstanceState.getParcelable("file_uri");
}



/**
 * Receiving activity result method will be called after closing the camera
 * */
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // if the result is capturing Image
    if (requestCode == CAMERA_CAPTURE_IMAGE_REQUEST_CODE) {
        if (resultCode == RESULT_OK) {

            // successfully captured the image
            // launching upload activity
            launchUploadActivity(true);


        } else if (resultCode == RESULT_CANCELED) {

            // user cancelled Image capture
            Toast.makeText(getApplicationContext(),
                    "User cancelled image capture", Toast.LENGTH_SHORT)
                    .show();

        } else {
            // failed to capture image
            Toast.makeText(getApplicationContext(),
                    "Sorry! Failed to capture image", Toast.LENGTH_SHORT)
                    .show();
        }

    } else if (requestCode == CAMERA_CAPTURE_VIDEO_REQUEST_CODE) {
        if (resultCode == RESULT_OK) {

            // video successfully recorded
            // launching upload activity
            launchUploadActivity(false);

        } else if (resultCode == RESULT_CANCELED) {

            // user cancelled recording
            Toast.makeText(getApplicationContext(),
                    "User cancelled video recording", Toast.LENGTH_SHORT)
                    .show();

        } else {
            // failed to record video
            Toast.makeText(getApplicationContext(),
                    "Sorry! Failed to record video", Toast.LENGTH_SHORT)
                    .show();
        }
    }
}

private void launchUploadActivity(boolean isImage){
    Intent i = new Intent(MainActivity.this, UploadActivity.class);
    i.putExtra("filePath", fileUri.getPath());
    i.putExtra("isImage", isImage);
    startActivity(i);
}

/**
 * ------------ Helper Methods ---------------------- 
 * */

/**
 * Creating file uri to store image/video
 */
public Uri getOutputMediaFileUri(int type) {
    return Uri.fromFile(getOutputMediaFile(type));
}

/**
 * returning image / video
 */
private static File getOutputMediaFile(int type) {

    // External sdcard location
    File mediaStorageDir = new File(
            Environment
                    .getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),
            Config.IMAGE_DIRECTORY_NAME);

    // Create the storage directory if it does not exist
    if (!mediaStorageDir.exists()) {
        if (!mediaStorageDir.mkdirs()) {
            Log.d(TAG, "Oops! Failed create "
                    + Config.IMAGE_DIRECTORY_NAME + " directory");
            return null;
        }
    }

    // Create a media file name
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss",
            Locale.getDefault()).format(new Date());
    File mediaFile;
    if (type == MEDIA_TYPE_IMAGE) {
        mediaFile = new File(mediaStorageDir.getPath() + File.separator
                + "IMG_" + timeStamp + ".jpg");
    } else if (type == MEDIA_TYPE_VIDEO) {
        mediaFile = new File(mediaStorageDir.getPath() + File.separator
                + "VID_" + timeStamp + ".mp4");
    } else {
        return null;
    }

    return mediaFile;
}
}`

下面是manifest.xml文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="info.androidhive.camerafileupload"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="11"
    android:targetSdkVersion="21" />

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="info.androidhive.camerafileupload.MainActivity"
        android:label="@string/app_name"
        android:screenOrientation="portrait" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name="info.androidhive.camerafileupload.UploadActivity"
        android:screenOrientation="portrait" >
    </activity>
</application>

</manifest>

---

请帮我修一下

这是由于：java.lang.NullPointerException:尝试在info.androidhive.camerafileupload.MainActivity.onCreate（MainActivity.java:46）的空对象引用上调用虚拟方法void android.app.ActionBar.setBackgroundDrawable（android.graphics.drawable.drawable）引起的

getActionBar（）

返回空值。@Simon是正确的。您需要做的就是学习如何读取堆栈跟踪（并从那里开始），尝试扩展ActionBarActivity