Android 获取空指针异常

可能重复：

这是我的CheckData.java

 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(); 

    testCertificates = null;

    DataManipulator.open();
    testCertificates = DataManipulator.getFirstCertificatesFromDB();
    DataManipulator.close();

    image.setImageBitmap(((Certificates) testCertificates).getBitmap());

    setContentView(layout);
}

} 这是第29行DataManipular.createCertificatesEntry（（证书）testCertificates）

这是我的DataManipular.java

    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;
    }    
}

这是第60行certificates.getBitmap（）.compress（Bitmap.CompressFormat.PNG，100，out）

这是我的logcat输出

06-04 11:09:41.824: E/AndroidRuntime(693): FATAL EXCEPTION: main
06-04 11:09:41.824: E/AndroidRuntime(693): java.lang.RuntimeException: Unable to start activity ComponentInfo{list.certificates/list.certificates.CheckData}: java.lang.NullPointerException
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.ActivityThread.access$600(ActivityThread.java:122)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.os.Handler.dispatchMessage(Handler.java:99)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.os.Looper.loop(Looper.java:137)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.ActivityThread.main(ActivityThread.java:4340)
06-04 11:09:41.824: E/AndroidRuntime(693):  at java.lang.reflect.Method.invokeNative(Native Method)
06-04 11:09:41.824: E/AndroidRuntime(693):  at java.lang.reflect.Method.invoke(Method.java:511)
06-04 11:09:41.824: E/AndroidRuntime(693):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-04 11:09:41.824: E/AndroidRuntime(693):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-04 11:09:41.824: E/AndroidRuntime(693):  at dalvik.system.NativeStart.main(Native Method)
06-04 11:09:41.824: E/AndroidRuntime(693): Caused by: java.lang.NullPointerException
06-04 11:09:41.824: E/AndroidRuntime(693):  at list.certificates.DataManipulator.createCertificatesEntry(DataManipulator.java:60)
06-04 11:09:41.824: E/AndroidRuntime(693):  at list.certificates.CheckData.onCreate(CheckData.java:29)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.Activity.performCreate(Activity.java:4465)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-04 11:09:41.824: E/AndroidRuntime(693):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
06-04 11:09:41.824: E/AndroidRuntime(693):  ... 11 more

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在您的情况下…我只能说您的

certificates

变量或

certificates.getBitmap（）

api返回null

Certificates testCertificates = new Certificates(BitmapFactory.decodeFile(Context.STORAGE_SERVICE));

在上面的代码中，需要图像的完整路径。您传递的不是文件的完整路径。因此，从上述两种情况来看，

certificates.getBitmap（）

是异常的最可能原因。不是图像的完整路径

一旦你有了图像的Uri。使用以下代码获取图像：

Bitmap bmp = MediaStore.Images.Media.getBitmap(getContentResolver(), uri);

Certificates testCertificates = new Certificates(bmp);

DataManipulator.open();
DataManipulator.createCertificatesEntry( (Certificates) testCertificates);
DataManipulator.close(); 

参考：

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签出后更新了我的全部代码…我正在从库中选择图像并将其保存到数据库，可能是，但我放在ans中的代码没有从库中拾取文件。它只是传递了错误的路径值。好的，但是还有其他方法吗？在屏幕上添加一个按钮，用户将单击该按钮浏览图像。将上面的代码移动到图像浏览按钮的处理程序。一旦你有了文件名，就使用它。这就是我所能说的，没有简短的回答。

Bitmap bmp = MediaStore.Images.Media.getBitmap(getContentResolver(), uri);

Certificates testCertificates = new Certificates(bmp);

DataManipulator.open();
DataManipulator.createCertificatesEntry( (Certificates) testCertificates);
DataManipulator.close();