当我单击按钮时引发空指针异常 [英] nullpointer exception raises when i click on the button

问题描述

当我在 android 上点击 CheckData button 时，它会抛出一个 nullpointer 异常.

When I click on CheckData button on android, it is throwing a nullpointer exception.

SaveData.java

public class SaveData extends Activity implements OnClickListener {     
    static final int DIALOG_ID = 0;

    private Uri mImageCaptureUri;
    private ImageView mImageView;   
    public static class Certificates {
    private Bitmap bmp;

        public Certificates(Bitmap b) {
        bmp = b;
        }
        public Bitmap getBitmap() { return bmp; }
    }

    private static final int PICK_FROM_CAMERA = 1;
    private static final int PICK_FROM_FILE = 2;

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

        View button1Click=findViewById(R.id.btn_choose);
        button1Click.setOnClickListener(this);
        View button2Click = findViewById(R.id.Button01add);
        button2Click.setOnClickListener(this);
        View button3Click = findViewById(R.id.Button01check);
        button3Click.setOnClickListener(this);  
    }

        public void onClick(View v){        
        switch(v.getId()){

        case R.id.Button01add:
            showDialog(DIALOG_ID);
            break;

        case R.id.Button01check:
            startActivity(new Intent (SaveData.this,CheckData.class));
            break;
        }

// picking an image from camera or gallery         
            final String [] items           = new String [] {"From Camera", "From SD Card"};                
            ArrayAdapter<String> adapter    = new ArrayAdapter<String> (this, android.R.layout.select_dialog_item,items);
            AlertDialog.Builder builder     = new AlertDialog.Builder(this);

            builder.setTitle("Select Image");
            builder.setAdapter( adapter, new DialogInterface.OnClickListener() {
                public void onClick( DialogInterface dialog, int item ) {
                    if (item == 0) {
                        Intent intent    = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                        File file        = new File(Environment.getExternalStorageDirectory(), "tmp_avatar_" + String.valueOf(System.currentTimeMillis()) + ".jpg");
                        mImageCaptureUri = Uri.fromFile(file);

                        try {           
                            intent.putExtra(android.provider.MediaStore.EXTRA_OUTPUT, mImageCaptureUri);
                            intent.putExtra("return-data", true);                           
                            startActivityForResult(intent, PICK_FROM_CAMERA);
                    }   catch (Exception e) {
                            e.printStackTrace();
                        }           

                        dialog.cancel();
                    } else {
                        Intent intent = new Intent();

                        intent.setType("image/*");
                        intent.setAction(Intent.ACTION_GET_CONTENT);

                        startActivityForResult(Intent.createChooser(intent, "Complete action using"), PICK_FROM_FILE);
                    }
                }
            } );

            final AlertDialog dialog = builder.create();

            mImageView = (ImageView) findViewById(R.id.image1);

            ((Button) findViewById(R.id.btn_choose)).setOnClickListener(new View.OnClickListener() {            
                @Override
                public void onClick(View v) {
                    dialog.show();
                }
            });
        }

        @Override
        protected void onActivityResult(int requestCode, int resultCode, Intent data) {
            if (resultCode != RESULT_OK) return;

            Bitmap bitmap   = null;
            String path     = "";

            if (requestCode == PICK_FROM_FILE) {
                mImageCaptureUri = data.getData(); 
                path = getRealPathFromURI(mImageCaptureUri); //from Gallery 

                if (path == null)
                    path = mImageCaptureUri.getPath(); //from File Manager

                if (path != null) 
                    bitmap  = BitmapFactory.decodeFile(path);
            } else {
                path    = mImageCaptureUri.getPath();
                bitmap  = BitmapFactory.decodeFile(path);
            }

            mImageView.setImageBitmap(bitmap);      
        }

        public String getRealPathFromURI(Uri contentUri) {
            String [] proj      = {MediaStore.Images.Media.DATA};
            Cursor cursor       = managedQuery( contentUri, proj, null, null,null);

            if (cursor == null) return null;

            int column_index    = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);

            cursor.moveToFirst();

            return cursor.getString(column_index);
        }

    protected final Dialog onCreateDialog(final int id) {
        Dialog dialog = null;
        switch(id) {
        case DIALOG_ID:
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setMessage("Information saved successfully ! Add Another Info?")
            .setCancelable(false)
            .setPositiveButton("No", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {

                    SaveData.this.finish();
              }
            })
        .setNegativeButton("Yes", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    dialog.cancel();
                }
            });
            AlertDialog alert = builder.create(); 
            dialog = alert;
            break;
        default:
        }
        return dialog;
    }
// menu option  
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.layout.mymenu, menu);        
        return true;
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if(item.getItemId() == R.id.item1) {
            Log.d("Option", "Save option is clicked");           
        }
        if(item.getItemId() == R.id.item2) {
            Log.d("Option", "Delete option is clicked");
        }
        if(item.getItemId() == R.id.item3) {
            Log.d("Option", "Exit option is clicked");
        }       
        return super.onOptionsItemSelected(item);       
    }
}

<小时>

DataManipulator.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;
    }    
}

DataManipulator.java:60 是 certificates.getBitmap().compress(Bitmap.CompressFormat.PNG, 100, out);

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);
    }
}

CheckData.java:29 是 DataManipulator.createCertificatesEntry( (Certificates) testCertificates);

Logcat 错误:

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

推荐答案

您从 certificates.getBitmap() 得到一个空值，因为那里没有位图.在您最初的任务中，您试图解码一个不存在的文件.使用 Context.STORAGE_SERVICE 不能那样工作，它只是一个等于 storage 的字符串.

You're getting a null from certificates.getBitmap() because there's not a bitmap there. In your initial assignment, you're trying to decode a file that doesn't exist. Using Context.STORAGE_SERVICE doesn't work that way, it's just a string equaling storage.

例如如何正确使用存储管理器的代码，请尝试 这个.

For example code of how to use a storage manager properly, try this.

如果您只是想解码资源(可绘制、原始等)，请使用另一种解码形式:

If you're just trying to decode a resource(drawable, raw, etc) use another form of decode:

InputStream is = context.getResources().openRawResource(resID);
Bitmap bitmap = BitmapFactory.decodeStream(is);

更新:假设我知道您要做什么，问题是您切换到 CheckData 活动而没有以任何方式传递所选位图.Activity 无法知道要使用什么位图，并且 Context.STORAGE_SERVICE 无论如何都不是位图，因此您无法对其进行解码.

Update: Assuming I know what it is you're trying to do, the problem is that you're switching to the CheckData activity without passing the selected bitmap in any way. The activity has no way of knowing what bitmap to use, and Context.STORAGE_SERVICE is not a bitmap in any way, so you can't decode it.

有关如何将位图传递给新活动的好答案，请查看此处.

For good answers on how to pass the bitmap to the new activity, look here.

简而言之，您可以将 mBitmap 变量添加到 SaveData，并将其传递给 CheckData.

In short, you could add an mBitmap variable to SaveData, and pass it along to CheckData.

为此，将 SaveData.onClick() 中的代码更改为:

For this, change the code in SaveData.onClick() to:

case R.id.Button01check:
    Intent intent = new Intent (SaveData.this,CheckData.class);
    intent.putExtra("bitmapData", mBitmap)
    startActivity(intent);
    break; 

并且，在onActivityResult()中，在最后添加:

And, in onActivityResult(), add this at the end:

mBitmap = bitmap;

在CheckData.onCreate()中:

Bitmap bmp = getIntent().getExtras().get("bitmapData");
if(bmp != null) {
    Certificates testCertificates = new Certificates(bmp);
} else {
    // Back out gracefully //
}

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