在运行相机照片上传的Android应用程序时，我得到零点异常。这可能是获取操作栏返回null。如果我的猜测是正确的，那么我应该添加一个空检查。
以下是日志猫
`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)`
我的mainactivity.java位于
之下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>
请帮我解决一下......