Question

在此发布之前，我已经在stackoverlfow上查看了其他相关帖子，但似乎没有什么能像我一样解决类似的问题。

这是我得到的错误：

06-29 21:02:38.274: E/AndroidRuntime(2261): FATAL EXCEPTION: main
06-29 21:02:38.274: E/AndroidRuntime(2261): Process: org.example.helloandroid, PID: 2261
06-29 21:02:38.274: E/AndroidRuntime(2261): java.lang.RuntimeException: Unable to start activity     ComponentInfo{org.example.helloandroid/org.example.helloandroid.QRGenActivity}: java.lang.NullPointerException
06-29 21:02:38.274: E/AndroidRuntime(2261):     at     android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at     android.app.ActivityThread.access$800(ActivityThread.java:135)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.os.Looper.loop(Looper.java:136)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.app.ActivityThread.main(ActivityThread.java:5017)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at java.lang.reflect.Method.invokeNative(Native Method)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at java.lang.reflect.Method.invoke(Method.java:515)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at dalvik.system.NativeStart.main(Native Method)
06-29 21:02:38.274: E/AndroidRuntime(2261): Caused by: java.lang.NullPointerException
06-29 21:02:38.274: E/AndroidRuntime(2261):     at org.example.helloandroid.QRGenActivity.onCreate(QRGenActivity.java:81)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.app.Activity.performCreate(Activity.java:5231)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-29 21:02:38.274: E/AndroidRuntime(2261):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-29 21:02:38.274: E/AndroidRuntime(2261):     ... 11 more

这是我应该生成QR码的QRGenerator代码，但它会抛出一个NPE。

public class QRGenActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);


    Intent intent = getIntent();
    String emailaddress = intent.getStringExtra("emailValue");
    String password = intent.getStringExtra("password");

    ImageView view = (ImageView) findViewById(R.id.qr);
    Log.d("EmailValue", emailaddress);
    Log.d("password", password);


    String qrInputText = emailaddress+"_"+password;
    Log.v("QR TAG", qrInputText);

    WindowManager manager = (WindowManager) getSystemService(WINDOW_SERVICE);
    Display display = manager.getDefaultDisplay();

    Point point = new Point();
    display.getSize(point);

    int width = point.x;
    int height = point.y;

    int smallerDimension = width < height ? width: height;
    smallerDimension*=3/4;

    com.google.zxing.Writer writer = new QRCodeWriter();
    String finalData = Uri.encode(qrInputText,"utf-8");

    try {
        BitMatrix bm = writer.encode(finalData, BarcodeFormat.QR_CODE, 150, 150);
        Bitmap ImageBitmap = Bitmap.createBitmap(150, 150, Config.ARGB_8888);

        for(int i=0;i<150;i++){
            for(int j=0;j<150;j++){
                ImageBitmap.setPixel(i, j, bm.get(i, j) ? Color.BLACK: Color.WHITE);
            }
        }

        if(ImageBitmap!=null){
Log.d("QRCreated", "QR Is created "+R.id.qr);

            view.setImageBitmap(ImageBitmap);
        }
        else{
            Toast.makeText(getApplicationContext(), "Some error occurred in generating QRCode", Toast.LENGTH_LONG).show();
        }
    } catch (WriterException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }



    Handler handler = new Handler();
setContentView(R.layout.display_qr);

getActionBar().setDisplayHomeAsUpEnabled(true);
}

Answer 1

你正在推出

ImageView view = (ImageView) findViewById(R.id.qr);

前

setContentView(R.layout.display_qr);

这不起作用，因为findViewById()在视图层次结构中搜索具有指定ID的视图，并且您还没有在该点添加任何视图。因此，它将返回null。这可能是导致事故的原因。

您应该在setContentView()之后立即移动super.onCreate()来电。

ZXing QR Code Generator应用程序崩溃与NPE

1 个答案: