Possible Duplicate:
nullpointer exception raises when i click on the button
当我单击Checkdata按钮时，我在CheckData.java DataManipulator.createCertificatesEntry（（Certificates）testCertificates）中得到nullpointer异常；
public class DataManipulator {
public static final String KEY_IMG = "image";
private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;
private static final String DATABASE_NAME = "DBtest";
private static final int DATABASE_VERSION = 1;
private static final String CERTIFICATES_TABLE = "certificates";
private static final String CREATE_CERTIFICATES_TABLE = "create table "+CERTIFICATES_TABLE+" (" +KEY_IMG+" blob not null) ";
private final Context mCtx;
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_CERTIFICATES_TABLE);
}
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS "+CERTIFICATES_TABLE);
onCreate(db);
}
}
public void Reset() { mDbHelper.onUpgrade(this.mDb, 1, 1); }
public DataManipulator(Context ctx) {
mCtx = ctx;
mDbHelper = new DatabaseHelper(mCtx);
}
public DataManipulator open() throws SQLException {
mDb = mDbHelper.getWritableDatabase();
return this;
}
public void close() { mDbHelper.close(); }
public void createCertificatesEntry(Certificates certificates) {
ByteArrayOutputStream out = new ByteArrayOutputStream();
certificates.getBitmap().compress(Bitmap.CompressFormat.PNG, 100, out);
ContentValues cv = new ContentValues();
cv.put(KEY_IMG, out.toByteArray());
mDb.insert(CERTIFICATES_TABLE, null, cv);
}
public Certificates getFirstCertificatesFromDB() throws SQLException {
Cursor cur = mDb.query(true, CERTIFICATES_TABLE, new String[] {KEY_IMG}, null, null, null, null, null, null);
if(cur.moveToFirst()) {
byte[] blob = cur.getBlob(cur.getColumnIndex(KEY_IMG));
ByteArrayInputStream inputStream = new ByteArrayInputStream(blob);
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
cur.close();
return new Certificates(bitmap);
}
cur.close();
return null;
}
}
这是DataManipulator.java certificate.getBitmap（）。compress（Bitmap.CompressFormat.PNG，100，out）的第60行;
public class CheckData extends ListActivity {
TextView selection;
DataManipulator dm;
private DataManipulator DataManipulator;
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.check);
dm = new DataManipulator(this);
LinearLayout layout = new LinearLayout(this);
ImageView image = new ImageView(this);
DataManipulator = new DataManipulator(this);
Certificates testCertificates = new Certificates(BitmapFactory.decodeFile(Context.STORAGE_SERVICE));
DataManipulator.open();
DataManipulator.createCertificatesEntry( (Certificates) testCertificates);
DataManipulator.close();
DataManipulator.close();
testCertificates = null;
DataManipulator.open();
testCertificates = DataManipulator.getFirstCertificatesFromDB();
DataManipulator.close();
image.setImageBitmap(((Certificates) testCertificates).getBitmap());
setContentView(layout);
}
}
这是我的CheckData.java第29行
DataManipulator.createCertificatesEntry（（Certificates）testCertificates）;
这是我的logcat
05-29 14:51:46.908: E/AndroidRuntime(741): FATAL EXCEPTION: main
05-29 14:51:46.908: E/AndroidRuntime(741): java.lang.RuntimeException: Unable to start activity ComponentInfo{list.certificates/list.certificates.CheckData}: java.lang.NullPointerException
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.ActivityThread.access$600(ActivityThread.java:122)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.os.Handler.dispatchMessage(Handler.java:99)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.os.Looper.loop(Looper.java:137)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.ActivityThread.main(ActivityThread.java:4340)
05-29 14:51:46.908: E/AndroidRuntime(741): at java.lang.reflect.Method.invokeNative(Native Method)
05-29 14:51:46.908: E/AndroidRuntime(741): at java.lang.reflect.Method.invoke(Method.java:511)
05-29 14:51:46.908: E/AndroidRuntime(741): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-29 14:51:46.908: E/AndroidRuntime(741): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-29 14:51:46.908: E/AndroidRuntime(741): at dalvik.system.NativeStart.main(Native Method)
05-29 14:51:46.908: E/AndroidRuntime(741): Caused by: java.lang.NullPointerException
05-29 14:51:46.908: E/AndroidRuntime(741): at list.certificates.DataManipulator.createCertificatesEntry(DataManipulator.java:60)
05-29 14:51:46.908: E/AndroidRuntime(741): at list.certificates.CheckData.onCreate(CheckData.java:29)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.Activity.performCreate(Activity.java:4465)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-29 14:51:46.908: E/AndroidRuntime(741): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
05-29 14:51:46.908: E/AndroidRuntime(741): ... 11 more
最佳答案
当您通过DataManipulator.createCertificatesEntry（（Certificates）testCertificates）行的Activity中为null的“ Object testCertificates”时；
DataManipulator.createCertificatesEntry方法中的certificate为null，因此certificate.getBitmap（）将在此处删除null指针
public void createCertificatesEntry(Certificates certificates)
{
ByteArrayOutputStream out = new ByteArrayOutputStream();
certificates.getBitmap().compress(Bitmap.CompressFormat.PNG, 100, out);
ContentValues cv = new ContentValues();
cv.put(KEY_IMG, out.toByteArray());
mDb.insert(CERTIFICATES_TABLE, null, cv);
}
所以要么检查一下createCertificatesEntry方法
要么
通过使用此行从Activity传递DataManipulator.createCertificatesEntry中的非null值
证书testCertificates =新证书（BitmapFactory.decodeFile（Context.STORAGE_SERVICE））;
以上
DataManipulator.createCertificatesEntry（（Certificates）testCertificates）;
关于android - 单击checkdata按钮时出现nullpointer异常，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/10794559/