Question

我刚刚创建了一个android对话框，根据此链接中的教程将结果返回给主机活动（在我的项目中，它是mainActivity）：http://developer.android.com/guide/topics/ui/dialogs.html

它说为了处理你想在对话框中做的事件，你应该在对话框类中使用interface。然后，在主机活动中，您应该实现此接口及其方法。但是我注意到它只在正面按钮点击时才会崩溃。这是我的代码：

  public class dialogFragement extends DialogFragment {


public interface NoticeDialogListener {
    public void onDialogPositiveClick(DialogFragment dialog);
    public void onDialogNegativeClick(DialogFragment dialog);
}

 NoticeDialogListener mListener;


@Override
public void onAttach(Activity activity) {


    // TODO Auto-generated method stub
    super.onAttach(activity);

    try {
        // Instantiate the NoticeDialogListener so we can send events to the host
        mListener = (NoticeDialogListener) activity;
    } catch (ClassCastException e) {
        // The activity doesn't implement the interface, throw exception
        throw new ClassCastException(activity.toString()
                + " must implement NoticeDialogListener");
    }
}



public Dialog onCreateDialog(Bundle savedInstanceState) {



    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());

    LayoutInflater inflater = getActivity().getLayoutInflater();


    builder.setView(inflater.inflate(R.layout.dialog_layout, null))
    // Add action buttons
           .setPositiveButton("Onayla", new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {
                   mListener.onDialogPositiveClick(dialogFragement.this);
               }
           })
           .setNegativeButton("İptal et", new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {
                   mListener.onDialogNegativeClick(dialogFragement.this);
               }
           });      
    return builder.create();
}


    }

主要活动：

public void onDialogPositiveClick(DialogFragment dialog) {

EditText et=(EditText)findViewById(R.id.editText1);
dosyaAdi=et.getText().toString();
dosyayaYaz();

 }

LogCat错误：

11-29 23:15:01.689: E/SensorManager(23506): thread start
11-29 23:15:16.684: E/AndroidRuntime(23506): FATAL EXCEPTION: main
11-29 23:15:16.684: E/AndroidRuntime(23506): java.lang.NullPointerException
11-29 23:15:16.684: E/AndroidRuntime(23506):    at          com.example.coordinates.MainActivity.onDialogPositiveClick(MainActivity.java:371)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at  com.example.coordinates.dialogFragement$1.onClick(dialogFragement.java:54)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:168)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at android.os.Looper.loop(Looper.java:137)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at android.app.ActivityThread.main(ActivityThread.java:4517)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at java.lang.reflect.Method.invokeNative(Native Method)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at java.lang.reflect.Method.invoke(Method.java:511)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
11-29 23:15:16.684: E/AndroidRuntime(23506):    at dalvik.system.NativeStart.main(Native Method)

dosyayaYaz（）函数：

private void dosyayaYaz(){


    sm.unregisterListener(this); // this is the line 213
    File myFile;  
    myFile= new File("sdcard/"+dosyaAdi.toString()+".csv");


        try {
            myFile.createNewFile();
        FileOutputStream fOut = new FileOutputStream(myFile);
        OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);

        myOutWriter.append("X Koor;Y Koor;Z Koor");
        myOutWriter.append("\n");


        dataReader=db.rawQuery("SELECT * FROM Koordinatlar", null);

        while(dataReader.moveToNext()){


            Float xDeg=(dataReader.getFloat(dataReader.getColumnIndex("xKoor")));
            Float yDeg=(dataReader.getFloat(dataReader.getColumnIndex("yKoor")));
            Float zDeg=(dataReader.getFloat(dataReader.getColumnIndex("zKoor")));


            myOutWriter.append(String.format("%f", xDeg)+";"+String.format("%f", yDeg)+";"+String.format("%f", zDeg));
            myOutWriter.append("\n");


        }


        Toast toast=Toast.makeText(getBaseContext(), "Başarıyla Dosyaya Yazıldı",Toast.LENGTH_SHORT);
        toast.show();
        sm.registerListener(this, myAccelerometer, SensorManager.SENSOR_DELAY_UI);

    } 
    catch(IOException ex){
        Toast toast=Toast.makeText(getBaseContext(), "Dosyaya yazma sırasında bir hata oluştu"+" "+ex.toString(),Toast.LENGTH_LONG);
        toast.show();
    }
}

onCreate函数：

 public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    fm=getFragmentManager();

    b1=(Button)findViewById(R.id.button1);
    b2=(Button)findViewById(R.id.button2);
    b3=(Button)findViewById(R.id.button3);
    x=(TextView)findViewById(R.id.textView4); 
    y=(TextView)findViewById(R.id.textView5); 
    z=(TextView)findViewById(R.id.textView6); 



    sm=(SensorManager)getSystemService(Context.SENSOR_SERVICE);

    myAccelerometer= sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

    sm.registerListener(this, myAccelerometer,SensorManager.SENSOR_DELAY_UI);

    veritabani= new VeriTabani(this);
    db=veritabani.getWritableDatabase();


    valuesX= new ArrayList<Float>();
    valuesY= new ArrayList<Float>();
    valuesZ= new ArrayList<Float>();
    zamanDiyagrami= new ArrayList<Float>();


     b1.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            grafikGoruntule();
        }
    });
     b2.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            verileriSil();
        }
    });

     b3.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            DialogFragment dialog = new dialogFragement();
            dialog.show(fm, "MyDialogFragment");
        }
    });


}

Answer 1

来自LogCat：

java.lang.NullPointerException 
    at com.example.coordinates.MainActivity.dosyayaYaz(MainActivity.java:213)

你的代码：

sm.unregisterListener(this); // this is the line 213

然后变量sm为null，需要用：

初始化它

sm = ...

<强>加成
根据您目前发布的内容，我不明白为什么sm是null。但是在dosyayaYaz()中，您可以随时执行此操作：

if(sm == null)
    sm=(SensorManager)getSystemService(Context.SENSOR_SERVICE);
sm.unregisterListener(this); // this is the line 213

（但最好尝试找出sm为null的确切原因。）

<强>加成
新的LogCat错误显示您正在尝试在MainActivity中查找实际上是DialogFragment的一部分的View ...也许在doPositiveClick()内可以使用：

public void onDialogPositiveClick(DialogFragment dialog) {
    //         Add this:  vvvvvvvvvvvvvvvvvvv
    EditText et=(EditText)dialog.getDialog().findViewById(R.id.editText1);
    ...

Answer 2

为了避免崩溃其良好做法，在调用它们之前总是检查null的监听器，所以你的代码看起来像这样

if(mListener != null)
    mListener.onDialogPositiveClick(dialogFragement.this);
// Similarly for negative button

错误的其他可能原因是因为您没有在主机活动中实现接口。您必须在通话活动中实施NoticeDialogListener。

正面点击时Android对话框崩溃

2 个答案: