Question

我正在尝试使用接口从AlertDialog.Builder.setPositiveButton的onClick事件发送click事件。

请帮帮我。我一直在寻找一个类似的问题用于指导。

NPE就在这条线上：

     mListener.onSetBalanceDialogPositiveClick(SetBalanceDialog.this);

这是LogCat：

08-19 20:05:50.469: E/AndroidRuntime(5795): FATAL EXCEPTION: main
08-19 20:05:50.469: E/AndroidRuntime(5795): java.lang.NullPointerException
08-19 20:05:50.469: E/AndroidRuntime(5795):     at com.smb.allowance.SetBalanceDialog$2.onClick(SetBalanceDialog.java:75)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:159)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at android.os.Looper.loop(Looper.java:123)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at android.app.ActivityThread.main(ActivityThread.java:3683)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at java.lang.reflect.Method.invokeNative(Native Method)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at java.lang.reflect.Method.invoke(Method.java:507)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:864)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
08-19 20:05:50.469: E/AndroidRuntime(5795):     at dalvik.system.NativeStart.main(Native Method)

这是Dialog代码：

package com.smb.allowance;

import java.text.DecimalFormat;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.view.inputmethod.InputMethodManager;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TextView.OnEditorActionListener;
import android.widget.Toast;

public class SetBalanceDialog extends DialogFragment implements OnEditorActionListener {

    private EditText editTextSetBalance;
    private static double dInput = 0;

    public interface SetBalanceDialogListener{
        public void onSetBalanceDialogPositiveClick(DialogFragment dialog);
    } // end interface

    SetBalanceDialogListener mListener;

    public void onAttache(Activity activity){
        super.onAttach(activity);

        try {
            mListener = (SetBalanceDialogListener) activity;
        }catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                        + " must implement SetBalanceDialogListener");
            }
    } // end onAttach

    public SetBalanceDialog(){
        // default empty constructor
    }// end constructor

    public Dialog onCreateDialog(Bundle savedInstanceState){

        View view = getActivity().getLayoutInflater().inflate(R.layout.dialog_balance_set, null);       

        editTextSetBalance = (EditText)view.findViewById(R.id.editTextSetBalance);

        editTextSetBalance.setOnClickListener(new View.OnClickListener() {      
            @Override
            public void onClick(View v) {
                    if (!editTextIsEmpty(editTextSetBalance)){
                        editTextSetBalance.setText("");
                    }

                    clearEditText(editTextSetBalance);
            }
        });

        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setView(view)
        .setCancelable(false)
        .setMessage(R.string.set_begin_balance)
        .setCancelable(false)
        .setPositiveButton(R.string.save, new DialogInterface.OnClickListener() {

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

        // show soft keyboard automatically 
        editTextSetBalance.requestFocus();
        editTextSetBalance.setOnEditorActionListener(this);

        return builder.create();

    } // end onCreateDialog

实现接口的Activity：

package com.smb.allowance;

import java.text.DecimalFormat;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.TextView.OnEditorActionListener;
import android.widget.Toast;

import com.smb.allowance.ResetBalanceDialogFragment.ResetBalanceDialogListener;

public class MainActivity extends FragmentActivity 
                implements ResetBalanceDialogListener,        SetBalanceDialog.SetBalanceDialogListener {

@Override
public void onSetBalanceDialogPositiveClick(DialogFragment dialog) {
    // For testing functionality
      onReset();
}

我是如何处理/错误处理EditText视图导致此NPE的？

我是初学Android / java和编程的新手，感谢您的帮助。

Answer 1

mListener为空

它是null，因为你永远不会将它分配给任何东西！（哦，是的，我听到你的想法！）但你没有

你有一个public void onAttache（Activity activity）`方法永远不会被调用，因为它应该是

public void onAttach(Activity activity)

您还应该为继承的方法添加@Override并调用super。如果您获取方法声明错误以及确保基类继承方法中的任何代码都运行，这将确保您收到编译错误。即使该方法在您使用的SDK版本中为空，也不意味着它在将来的某个未知点上不会为空。

Answer 2

检查您的拼写是否有重写方法：

public void onAttache(Activity activity)

应该是

public void onAttach(Activity activity)

在调用它们之前检查null的侦听器也是一种很好的做法。

NullPointerException当对话框正面按钮onClick调用接口时

2 个答案: