我有一个 ViewPager 的活动。我正在使用它来滑动图像。我还有一个保存按钮，我需要将当前图像保存到 SD 卡。但我得到一个错误。这是我的 XML 文件：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/rl_view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clickable="true"
android:focusable="true"
android:focusableInTouchMode="true" >
<android.support.v4.view.ViewPager
android:id="@+id/view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<Button
android:id="@+id/bSave"
android:layout_width="80dp"
android:layout_height="40dp"
android:layout_alignParentTop="true"
android:layout_marginLeft="15dp"
android:layout_marginTop="15dp"
android:text="Save"
android:layout_alignParentLeft="true"
android:textSize="24sp"
android:padding="0dp"
android:background="@drawable/buttons" />
</RelativeLayout>
这是我的课：
public class Photo_gallery extends Activity implements OnClickListener{
Button save;
final File myDir = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Pictures/Images/");
boolean success = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.photo_gallery);
save = (Button) findViewById(R.id.bSave);
final ViewPager viewPager = (ViewPager) findViewById(R.id.view_pager);
ImagePagerAdapter adapter = new ImagePagerAdapter();
viewPager.setAdapter(adapter);
save.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
final Random generator = new Random();
int n = 10000;
n = generator.nextInt(n);
final String fname = "StyleMe-" + n + ".png";
myDir.mkdirs();
File image = new File(myDir, fname);
BitmapDrawable drawable = (BitmapDrawable) viewPager.getBackground();
Bitmap bitmap = drawable.getBitmap();
// Encode the file as a PNG image.
FileOutputStream outStream;
try {
outStream = new FileOutputStream(image);
bitmap.compress(Bitmap.CompressFormat.PNG, 100, outStream);
/* 100 to keep full quality of the image */
outStream.flush();
outStream.close();
success = true;
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
if (success) {
Toast.makeText(getApplicationContext(), "Image saved with success at /sdcard/Pictures/SexyImages",
Toast.LENGTH_LONG).show();
} else {
Toast.makeText(getApplicationContext(),
"Error during image saving", Toast.LENGTH_LONG).show();
}
sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED, Uri.parse
("file://"
+ Environment.getExternalStorageDirectory())));
}
});
}
private class ImagePagerAdapter extends PagerAdapter {
private int[] mImages = new int[] {
R.drawable.p1,
R.drawable.p2,
R.drawable.p3,
.
.
.
.
R.drawable.p108
};
@Override
public int getCount() {
return mImages.length;
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == ((ImageView) object);
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
Context context = Photo_gallery.this;
ImageView imageView = new ImageView(context);
int padding = context.getResources().getDimensionPixelSize(
R.dimen.padding_medium);
imageView.setPadding(padding, padding, padding, padding);
imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
imageView.setImageResource(mImages[position]);
((ViewPager) container).addView(imageView, 0);
return imageView;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
((ViewPager) container).removeView((ImageView) object);
}
}
public void onClick(View arg0) {
// TODO Auto-generated method stub
}
}
我在这一行收到错误（java.lang.NullPointerException）：
Bitmap bitmap = drawable.getBitmap();