Java 无法删除Webview自定义AlertDialog提示符（）中的空间

似乎无法理解为什么不能通过按backspace删除自定义AlertDialog prompt（）中的空格。我可以删除所有其他文本，但不能删除空格。我使用以下代码来定制prompt（）

public boolean onJsPrompt(WebView view, String url, String message,
                                      String defaultValue, final JsPromptResult result) {
                final AlertDialog.Builder builder = new AlertDialog.Builder(view.getContext());

                builder.setTitle("").setMessage(message);

                final EditText et = new EditText(view.getContext());
                et.setSingleLine();
                et.setText(defaultValue);
                builder.setView(et)
                        .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                result.confirm(et.getText().toString());
                            }

                        })
                        .setNeutralButton("cancel", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int which) {
                                result.cancel();
                            }
                        });

        // Shield keycode equal to 84 and other keys, to avoid the dialog box after the button message and the page can no longer pop up the dialog box
                builder.setOnKeyListener(new DialogInterface.OnKeyListener() {
                    public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) {
                        Log.v("onJsPrompt", "keyCode==" + keyCode + "event="+ event);
                        return true;
                    }
                });

                AlertDialog dialog = builder.create();
                dialog.show();
                return true;
            }