Android 工作室“尝试在空对象引用上调用虚方法”

Question

我无法克服这个“尝试在空对象引用上调用虚拟方法”错误。

所以我的 Button 在下面的代码中打开一个 CustomDialog 和一个 EditText 用户可以在其中更新他的电子邮件地址。

        btnChangeEmail=(Button)findViewById(R.id.buttonChangeEmail);
        btnChangeEmail.setOnClickListener(new OnClickListener() {
            @Override

            //Change Email Dialog
            public void onClick (View arg0){
                final Dialog dialog = new Dialog(context);
                dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
                dialog.setContentView(R.layout.email_dialog);
                //dialog.setCancelable(false);
                dialog.setCanceledOnTouchOutside(false);

                Button dialogButton = (Button) dialog.findViewById(R.id.buttonSave);
                dialogButton.setOnClickListener(new OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        EditText txtNewEmail = (EditText)findViewById(R.id.editTextNewEmail);
                        AlertDialog.Builder alert = new AlertDialog.Builder(context);
                        alert.setTitle("Are you sure?");
                        alert.setMessage("Use " + txtNewEmail.getText().toString() + " as your new address?");
                        alert.setCancelable(false);
                        alert.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {

                            }
                        });
                        alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {

                                dialog.dismiss();
                            }
                        });
                        AlertDialog alertDialog = alert.create();
                        alertDialog.show();
                    }
                });

                Button exitButton = (Button) dialog.findViewById(R.id.buttonExit);
                exitButton.setOnClickListener(new OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        dialog.dismiss();
                    }
                });

                dialog.show();
                Window window = dialog.getWindow();
                float h = (float) (getResources().getDisplayMetrics().heightPixels * .9);
                float w = (float) (getResources().getDisplayMetrics().widthPixels);
                int height = (int) h;
                int width = (int) w;
                window.setLayout(width, height);
            }
        }

通过单击上述自定义对话框中的保存按钮，它会打开一个警报，提示用户是否真的想继续并覆盖他注册的电子邮件地址。我清楚地实例化了 txtNewEmail 但总是在它说

的那一行得到空对象引用错误

alert.setMessage("Use " + txtNewEmail.getText().toString() + "作为你的新地址？");

感谢任何帮助。谢谢。

这是我的完整 logcat 错误...

03-05 01:51:57.704 4512-4512/? E/AndroidRuntime: FATAL EXCEPTION: main
                                             Process: com.example.twenty, PID: 4512
                                             java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
                                                 at com.example.twenty.SettingsActivity.onClick(SettingsActivity.java:193)
                                                 at android.view.View.performClick(View.java:5198)
                                                 at android.view.View$PerformClick.run(View.java:21147)
                                                 at android.os.Handler.handleCallback(Handler.java:739)
                                                 at android.os.Handler.dispatchMessage(Handler.java:95)
                                                 at android.os.Looper.loop(Looper.java:148)
                                                 at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Answer 1

删除并添加在 Listener 之外发起的 txtNewEmail

final EditText txtNewEmail = (EditText)findViewById(R.id.editTextNewEmail);
btnChangeEmail=(Button)findViewById(R.id.buttonChangeEmail);

Answer 2

EditText txtNewEmail = (EditText)findViewById(R.id.editTextNewEmail);

此对象为空(txtNewEmail) 由视图父调用此方法(findViewById)

改变

  alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {

                            dialog.dismiss();
                        }
                    });

和

  alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {

                            alert.dismiss();
                        }
                    });

Answer 3

您在 onClickListener 中的 edittext 也将像这样使用对话框来查找 id

EditText txtNewEmail = (EditText)dialog.findViewById(R.id.editTextNewEmail);

Android 工作室“尝试在空对象引用上调用虚方法”

Android studio “ Attempt to invoke virtual method on a null object reference”

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