颤振:键盘出现时背景图像被挤压

看起来您只需要移动背景图像就可以成为父窗口小部件。即

return new Scaffold(
        appBar: new AppBar(
          title: new Text(widget.title),
        ),
        body: Container(
            width: double.infinity,
            height: double.infinity,
            decoration: BoxDecoration(
              image: DecorationImage(
                  image: ExactAssetImage('assets/images/bg.png'),
                  fit: BoxFit.fill,
                  alignment:Alignment.topCenter,
                  ),     
            ),
            child: Stack(
              children: <Widget>[
                Container(
                  child: SingleChildScrollView(
                    padding: EdgeInsets.all(width * 0.10),
                    child: Column(
                      crossAxisAlignment: CrossAxisAlignment.stretch,
                      children: <Widget>[
                        SizedBox(
                          height: height * 0.10,
                        ),
                        Container(
                          decoration: BoxDecoration(color: Colors.transparent),
                          child: Container(
                            margin: EdgeInsets.only(
                                bottom: height * 0.02, left: 20.0, right: 20.0),
                            child: Image.asset('assets/images/logo.png'),
                          ),
                        ),
                        SizedBox(
                          height: height * 0.05,
                        ),
                        Container(
                            decoration:
                                BoxDecoration(color: Colors.transparent),
                            child: Container()
                            new Form(
                                key: _formKey,
                                autovalidate: _autoValidate,
                                child: LoginFrom(width, height))
                                ),
                      ],
                    ),
                  ),
                ),
              ],
            )) // This trailing comma makes auto-formatting nicer for build methods.
        );