android - 如何从一个班级去另一个班级

Question

我正在制作一个在捕获 qr 代码时读取 qr 代码的应用程序，我的 scrren 应该移动到另一个类，但它显示空指针异常

我的代码CameraTestActivity.java是

/*
 * Basic no frills app which integrates the ZBar barcode scanner with
 * the camera.
 * 
 * Created by lisah0 on 2012-02-24
 */
package net.sourceforge.zbar.android.CameraTest;

import net.sourceforge.zbar.Config;
import net.sourceforge.zbar.Image;
import net.sourceforge.zbar.ImageScanner;
import net.sourceforge.zbar.Symbol;
import net.sourceforge.zbar.SymbolSet;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.pm.ActivityInfo;
import android.hardware.Camera;
import android.hardware.Camera.AutoFocusCallback;
import android.hardware.Camera.PreviewCallback;
import android.hardware.Camera.Size;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.TextView;

public class CameraTestActivity extends Activity {
private Camera mCamera;
private CameraPreview mPreview;
private Handler autoFocusHandler;

TextView scanText;
Button scanButton;
Intent i;
Context context;

ImageScanner scanner;

private boolean barcodeScanned = false;
private boolean previewing = true;

static {
    System.loadLibrary("iconv");
}

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

    autoFocusHandler = new Handler();
    mCamera = getCameraInstance();

    /* Instance barcode scanner */
    scanner = new ImageScanner();
    scanner.setConfig(0, Config.X_DENSITY, 3);
    scanner.setConfig(0, Config.Y_DENSITY, 3);

    mPreview = new CameraPreview(this, mCamera, previewCb, autoFocusCB);
    FrameLayout preview = (FrameLayout) findViewById(R.id.cameraPreview);
    preview.addView(mPreview);

    scanText = (TextView) findViewById(R.id.scanText);

    scanButton = (Button) findViewById(R.id.ScanButton);

    scanButton.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            if (barcodeScanned) {
                barcodeScanned = false;
                scanText.setText("Scanning...");
                mCamera.setPreviewCallback(previewCb);
                mCamera.startPreview();
                previewing = true;
                mCamera.autoFocus(autoFocusCB);
            }
        }
    });
}

public void onPause() {
    super.onPause();
    releaseCamera();
}

/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance() {
    Camera c = null;
    try {
        c = Camera.open();
    } catch (Exception e) {
    }
    return c;
}

private void releaseCamera() {
    if (mCamera != null) {
        previewing = false;
        mCamera.setPreviewCallback(null);
        mCamera.release();
        mCamera = null;
    }
}

private Runnable doAutoFocus = new Runnable() {
    public void run() {
        if (previewing)
            mCamera.autoFocus(autoFocusCB);
    }
};

PreviewCallback previewCb = new PreviewCallback() {
    public void onPreviewFrame(byte[] data, Camera camera) {
        Camera.Parameters parameters = camera.getParameters();
        Size size = parameters.getPreviewSize();

        Image barcode = new Image(size.width, size.height, "Y800");
        barcode.setData(data);

        int result = scanner.scanImage(barcode);

        if (result != 0) {
            previewing = false;
            mCamera.setPreviewCallback(null);
            mCamera.stopPreview();

            SymbolSet syms = scanner.getResults();
            for (Symbol sym : syms) {
                scanText.setText("barcode result " + sym.getData());
                barcodeScanned = true;
                i = new Intent(context, beginmove.class);
                startActivity(i);

            }

        }


    }
};



// Mimic continuous auto-focusing
AutoFocusCallback autoFocusCB = new AutoFocusCallback() {
    public void onAutoFocus(boolean success, Camera camera) {
        autoFocusHandler.postDelayed(doAutoFocus, 1000);
    }
};
}


CameraPreview. java


/*
 * Barebones implementation of displaying camera preview.
 * 
 * Created by lisah0 on 2012-02-24
 */
package net.sourceforge.zbar.android.CameraTest;

import java.io.IOException;

import android.app.Activity;
import android.os.Bundle;

import android.util.Log;

import android.view.View;
import android.view.Surface;
import android.view.SurfaceView;
import android.view.SurfaceHolder;

import android.content.Context;

import android.hardware.Camera;
import android.hardware.Camera.PreviewCallback;
import android.hardware.Camera.AutoFocusCallback;
import android.hardware.Camera.Parameters;

/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
private SurfaceHolder mHolder;
private Camera mCamera;
private PreviewCallback previewCallback;
private AutoFocusCallback autoFocusCallback;

public CameraPreview(Context context, Camera camera,
                     PreviewCallback previewCb,
                     AutoFocusCallback autoFocusCb) {
    super(context);
    mCamera = camera;
    previewCallback = previewCb;
    autoFocusCallback = autoFocusCb;

    /* 
     * Set camera to continuous focus if supported, otherwise use
     * software auto-focus. Only works for API level >=9.
     */
    /*
    Camera.Parameters parameters = camera.getParameters();
    for (String f : parameters.getSupportedFocusModes()) {
        if (f == Parameters.FOCUS_MODE_CONTINUOUS_PICTURE) {
            mCamera.setFocusMode(Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
            autoFocusCallback = null;
            break;
        }
    }
    */

    // Install a SurfaceHolder.Callback so we get notified when the
    // underlying surface is created and destroyed.
    mHolder = getHolder();
    mHolder.addCallback(this);

    // deprecated setting, but required on Android versions prior to 3.0
    mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}

public void surfaceCreated(SurfaceHolder holder) {
    // The Surface has been created, now tell the camera where to draw the preview.
    try {
        mCamera.setPreviewDisplay(holder);
    } catch (IOException e) {
        Log.d("DBG", "Error setting camera preview: " + e.getMessage());
    }
}

public void surfaceDestroyed(SurfaceHolder holder) {
    // Camera preview released in activity
}

public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
    /*
     * If your preview can change or rotate, take care of those events here.
     * Make sure to stop the preview before resizing or reformatting it.
     */
    if (mHolder.getSurface() == null){
      // preview surface does not exist
      return;
    }

    // stop preview before making changes
    try {
        mCamera.stopPreview();
    } catch (Exception e){
      // ignore: tried to stop a non-existent preview
    }

    try {
        // Hard code camera surface rotation 90 degs to match Activity view in portrait
        mCamera.setDisplayOrientation(90);

        mCamera.setPreviewDisplay(mHolder);
        mCamera.setPreviewCallback(previewCallback);
        mCamera.startPreview();
        mCamera.autoFocus(autoFocusCallback);
    } catch (Exception e){
        Log.d("DBG", "Error starting camera preview: " + e.getMessage());
    }
}
}

现在我想abc.java在扫描并获取数据后去上课我应该怎么去那里

Answer 1

Class2 cls2=新的 Class2(); cls2.UpdateEmployee();

在你的 Class1 中定义

Answer 2

i have done same thing here
public class CategoryList extends Activity implements OnItemClickListener, OnClickListener {

    // All static variables
    static final String categoryURL = "api";

    // XML node keys
    static final String KEY_GATEGORY= "Category";

    static final String KEY_CAT_ID = "cat_id";
    static final String KEY_CAT_NAME = "cat_name";
    String msg="";
    DatabaseHelper dbHelper;
    TextView tvmsg;
    EditText etCategoryName;
    Button btnEdit,btnAdd;
    ListView lvCategory;
    ArrayList<Category> categoryList;
    CategoryAdapterHelper ca;
    Cursor records;
    Dialog dialog; 
    Document doc;
    XMLParser parser;
    int flag=0;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.category);
        initComponant();
        //      setDatabase();
        (new AsyncTaskExample()).execute("");

    }
    private class AsyncTaskExample extends AsyncTask<String, Void, String> {
        // private String Content;
        private ProgressDialog Dialog;
        String response = "";

        @Override
        protected void onPreExecute() {
            Dialog = new ProgressDialog(CategoryList.this);
            Dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
            Dialog.setMessage("Loading android tutorial...");
            Dialog.setCancelable(false);
            Dialog.show();

        }
        @Override
        protected String doInBackground(String... urls) {

            try {
                doc = parser.getXmlFromUrl(categoryURL);
            } catch (SAXException e) {
                e.printStackTrace();
            }
            if(doc!= null){

                NodeList ner1=doc.getElementsByTagName(KEY_GATEGORY);
                for (int j = 0; j < ner1.getLength(); j++) 
                {
                    Element e1 = (Element) ner1.item(j);
                    int id=Integer.parseInt(parser.getValue(e1,KEY_CAT_ID));
                    String name=parser.getValue(e1,KEY_CAT_NAME );
                    Cursor c=dbHelper.selectRecord(true,id);
                    if(c.getCount()==0)
                        dbHelper.inserRecord(id,name);
                }

            }
            else{
                Toast.makeText(CategoryList.this, "Sorry Unable to retrive data. Please try again later", Toast.LENGTH_LONG).show();
            }

            return response;
        }
        @Override
        protected void onPostExecute(String result) {
            Dialog.dismiss();
            displayCategory();

        }
    }
    private void initComponant() {
        // TODO Auto-generated method stub
        categoryList=  new ArrayList<Category>();
        lvCategory=(ListView)findViewById(R.id.Category_listCategory);
        lvCategory.setOnItemClickListener(this);

        btnAdd=(Button)findViewById(R.id.Category_btnAdd);
        btnAdd.setOnClickListener(this);
        btnEdit=(Button)findViewById(R.id.Category_btnEdit);
        btnEdit.setOnClickListener(this);
        dialog= new Dialog(CategoryList.this);
        dialog.setContentView(R.layout.customdialog);
        dialog.setTitle("Navigation Application");
        dbHelper=new DatabaseHelper(this);
        parser = new XMLParser();
        doc = null;

    }

    private void displayCategory() {
        // TODO Auto-generated method stub
        lvCategory.setAdapter(null);
        categoryList=  new ArrayList<Category>();
        try
        {
            records=dbHelper.selectRecord();
            startManagingCursor(records);
            if(records.getCount()>0)
            {
                btnEdit.setEnabled(true);
                records.moveToFirst();
                while(!records.isAfterLast())
                {
                    categoryList.add(new Category(records.getInt(records.getColumnIndex("_categoryid")),records.getString(records.getColumnIndex("name"))));
                    records.moveToNext();
                }
                ca=new CategoryAdapterHelper(this, categoryList,flag);
                lvCategory.setAdapter(ca);
            }
            else
            {
                btnEdit.setEnabled(false);
                new DialogDisplay().showDialog(dialog,"Game Category Not Define Yet.!");
            }
        }
        catch (Exception e) {
            // TODO: handle exception
        }
    }
    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        displayCategory();
    }
    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch(v.getId())
        {
        case R.id.Category_btnAdd:
            Intent newCategory=new Intent(CategoryList.this,NewCategory.class);
            startActivity(newCategory);
            break;
        case R.id.Category_btnEdit:
            if(btnEdit.getText().toString().equals("Edit"))
            {
                flag=1;
                btnEdit.setText("Done");
            }
            else
            {
                flag=0;
                btnEdit.setText("Edit");
            }
            displayCategory();
            break;
        }

    }
    class CategoryAdapterHelper extends BaseAdapter  {

        Context context;
        int flag;
        public ArrayList<Category> categoryList;
        public CategoryAdapterHelper(Context c,ArrayList<Category> categoryList,int flag) {
            // TODO Auto-generated constructor stub
            context=c;
            this.categoryList=categoryList;
            this.flag=flag;
        }
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return categoryList.size();
        }

        @Override
        public Object getItem(int position) {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            Category category=categoryList.get(position);
            return category.id;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            View view = convertView;
            if (view == null) {
                LayoutInflater vi= LayoutInflater.from(context);
                view = vi.inflate(R.layout.category_detail,null);
            }
            Category category= categoryList.get(position);
            if (category!= null) 
            {
                TextView name = (TextView) view.findViewById(R.id.Category_detail_name);
                final ImageView image=(ImageView)view.findViewById(R.id.Category_detail_imageView1);
                if (name != null) 
                {
                    name.setText(category.categoryName);
                    if(flag==1)
                    {
                        image.setBackgroundResource(R.drawable.delete);
                        image.setTag(position);
                        image.setOnClickListener(new OnClickListener() {

                            @Override
                            public void onClick(View v) 
                            {// TODO Auto-generated method stub
                                final int id=(int)getItemId(Integer.parseInt(image.getTag().toString()));
                                final AlertDialog.Builder dlgAlert  = new AlertDialog.Builder(context);
                                dlgAlert.setMessage("Do you want to delete it?\nIt will deleted all the Games..!");
                                dlgAlert.setTitle("Nevigation Application");
                                dlgAlert.setPositiveButton("Delete",new DialogInterface.OnClickListener()
                                {

                                    @Override
                                    public void onClick(DialogInterface dialog,
                                            int which) {
                                        // TODO Auto-generated method stub
                                        DatabaseHelper dbHelper=new DatabaseHelper(context);
                                        dbHelper.deleteRecord("category", id);
                                        displayCategory();
                                    }

                                });
                                dlgAlert.setNegativeButton("cancel",new DialogInterface.OnClickListener()
                                {

                                    @Override
                                    public void onClick(DialogInterface dialog,
                                            int which) {
                                        // TODO Auto-generated method stub
                                        dialog.dismiss();
                                    }

                                });
                                dlgAlert.show();
                            }
                        });
                    }
                }
            }
            return view;
        }

    }
    @Override
    public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
        // TODO Auto-generated method stub

        if(btnEdit.getText().toString().equals("Edit"))
        {
            Category category=categoryList.get(arg2);
            Toast.makeText(CategoryList.this,""+category.id,Toast.LENGTH_SHORT).show();
            Intent gameIntent=new Intent(CategoryList.this,GameList.class);
            gameIntent.putExtra("categoryid",category.id);
            gameIntent.putExtra("categoryname", category.categoryName);
            startActivity(gameIntent);
        }
    }

}