为了学习目的,我正在创建一个文件管理器。我刚开始学习颤抖,所以我对它没有多少了解。
我的问题是我想在文件夹中显示图像的缩略图,因为我使用ListView中的FutureBuilder调用用本机代码编写的函数。它工作正常,但每当我打开一个包含大量图像的目录时,它会冻结UI一段时间。即使异步调用缩略图,我也无法滚动它。
Listview的代码: -
@override
Widget build(BuildContext context) {
return new ListView.builder(
itemBuilder: (itemContext, i) {
if (_filesList != null && i < _filesList.length) {
String currDir = _filesList[i]['path'];
return new ListTile(
title: new Text(_filesList[i]['name']),
leading: (_filesList[i]['isDir'] == "false")
? new FutureBuilder<Uint8List>(
future: _getThumbnail(currDir),
builder: (BuildContext context,
AsyncSnapshot<Uint8List> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return new Container(
decoration: new BoxDecoration(
color: Colors.brown,
borderRadius: new BorderRadius.circular(20.0),
),
width: 30.0,
height: 30.0,
);
default:
if (snapshot.hasError)
return new Container(
decoration: new BoxDecoration(
color: Colors.brown,
borderRadius: new BorderRadius.circular(20.0),
),
width: 30.0,
height: 30.0,
);
else {
return new Image.memory(snapshot.data);
}
}
},
)
: new Container(
decoration: new BoxDecoration(
color: (_filesList[i]['isDir'] == "true")
? Colors.yellow
: Colors.brown,
borderRadius: new BorderRadius.circular(20.0),
),
width: 30.0,
height: 30.0),
onTap: () {
setState(() {
_currentDir = currDir;
});
_getFilesList(currDir);
},
);
} else {
return null;
}
},
);
}
_getThumbnail()的代码: -
Future <Uint8List> _getThumbnail(path) async {
try {
String thumbnailString =
await channel.invokeMethod("getThumbnail", {"path": path});
thumbnailString = thumbnailString.replaceAll('\n', '');
Uint8List bytes = BASE64.decode(thumbnailString);
return bytes;
} on PlatformException catch (e) {
print("Files Not Found $e{e.message}");
return null;
}
}
答案 0 :(得分:0)
即使在Flutter中调用是异步的,Android上处理getThumbnail
的代码也可能阻塞UI线程,从而导致冻结加载或断断续续的滚动。一种解决方案是使用AsyncTask在doInBackground
中建立/获取缩略图,并在onPostExecute
中返回结果。