在對App進行數據加載的時候，會遇到沒有網的情況，這個時候，我們會想對上一次加載的數據進行緩存，避免頁面出現空白的情況，這種情況一般在加載成功之后，保存到本地，然后在下次加載錯誤的時候，展示上次的數據就行了，但是會有一個例外，就是當用戶第一次下載app，當時并沒有打開，在無網的情況下打開了app，這個時候，并沒有緩存上一次加載成功的數據，也會出現頁面數據大面積的空白的情況（一般公司沒這個要求。。。然而我這xx公司)。
解決方式：將初始化數據放在assets目錄下，在啟動app，例如在閃屏頁中復制到本地，然后在第一次打開app加載錯誤的時候，讀取緩存的數據，在下次加載成功之后，使用上一次的數據，可以說該預埋數據只是在上述情況才會有用。看代碼：
public class AssetCopyer {
private String asset_list_fileName;
private final Context mContext;
private final AssetManager mAssetManager;
private File mAppDirectory;
public AssetCopyer(Context context, String asset_list_fileName) {
mContext = context;
mAssetManager = context.getAssets();
this.asset_list_fileName = asset_list_fileName;
}
/**
* 將assets目錄下指定的文件拷貝到sdcard中
* @return 是否拷貝成功,true 成功；false 失敗
* @throws IOException
*/
public boolean copy() throws IOException {
List<String> srcFiles = new ArrayList<>();
//獲取系統在SDCard中為app分配的目錄，eg:/sdcard/Android/data/$(app's package)
//該目錄存放app相關的各種文件(如cache，配置文件等)，unstall app后該目錄也會隨之刪除
mAppDirectory = mContext.getExternalFilesDir(null);
if (null == mAppDirectory) {
return false;
}
//讀取assets/$(subDirectory)目錄下的assets.lst文件，得到需要copy的文件列表
List<String> assets = getAssetsList();
for( String asset : assets ) {
//如果不存在，則添加到copy列表
if( ! new File(mAppDirectory,asset).exists() ) {
srcFiles.add(asset);
}
}
//依次拷貝到App的安裝目錄下
for( String file : srcFiles ) {
copy(file);
}
return true;
}
/**
* 獲取需要拷貝的文件列表（記錄在assets/assets.lst文件中）
* @return 文件列表
* @throws IOException
*/
protected List<String> getAssetsList() throws IOException {
List<String> files = new ArrayList<>();
InputStream listFile = mAssetManager.open(new File(asset_list_fileName).getPath());
BufferedReader br = new BufferedReader(new InputStreamReader(listFile));
String path;
while (null != (path = br.readLine())) {
files.add(path);
}
return files;
}
/**
* 執行拷貝任務
* @param asset 需要拷貝的assets文件路徑
* @return 拷貝成功后的目標文件句柄
* @throws IOException
*/
protected File copy( String asset ) throws IOException {
InputStream source = mAssetManager.open(new File(asset).getPath());
File destinationFile = new File(mAppDirectory, asset);
if(destinationFile.exists()){
return destinationFile;
}
destinationFile.getParentFile().mkdirs();
OutputStream destination = new FileOutputStream(destinationFile);
byte[] buffer = new byte[1024];
int nread;
while ((nread = source.read(buffer)) != -1) {
if (nread == 0) {
nread = source.read();
if (nread < 0)
break;
destination.write(nread);
continue;
}
destination.write(buffer, 0, nread);
}
destination.close();
return destinationFile;
}
}
上面是一個拷貝到app目錄下的工具類（/sdcard/Android/data/$(app's package))，拷貝原理是，先將assets目錄下的需要拷貝的文件名字添加到一個.text文本文件中 eg：
assets.lst.txt
home_banner_01.png
shop_banner_01.png
shop_item_01.png
shop_item_02.png
shop_item_03.png
shop_item_04.png
shop_item_05.png
shop_item_06.png
shop_item_07.png
shop_item_08.png
shop_item_09.png
shop_label_01.png
shop_label_02.png
assets目錄：
Paste_Image.png
最后是兩個json文件(緩存的策略是使用SharedPreferences 保存json數據，但是圖片無法緩存，這個時候就需要將json中的url對應保存在本地的文件名字)。
貼一段json：image_url就是對應的app目錄下的文件
{
"banner_list": [
{
"img": "\/sdcard\/Android\/data\/niubi\/files\/shop_banner_01.png"
}
],
"note_list": [],
"shop_list": [
{
"icon": "",
"title": "",
"goods_list_url": "https:\/\/niubi\/shop\/goods\/0\/category-list",
"category": [
{
"row": 1,
"col": 3,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_01.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/0\/category-list"
}
]
},
{
"icon": "\/sdcard\/Android\/data\/niubi\/files\/shop_label_01.png",
"title": "Apple",
"goods_list_url": "https:\/\/niubi\/shop\/goods\/91\/category-list",
"category": [
{
"row": 1,
"col": 1,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_02.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/detail_redirect\/1941"
},
{
"row": 1,
"col": 1,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_03.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/detail_redirect\/1931"
},
{
"row": 1,
"col": 1,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_04.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/detail_redirect\/1921"
},
{
"row": 1,
"col": 3,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_05.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/91\/category-list"
}
]
},
{
"icon": "\/sdcard\/Android\/data\/niubi\/files\/shop_label_02.png",
"title": "\u7f8e\u5986",
"goods_list_url": "https:\/\/niubi\/shop\/goods\/34\/category-list",
"category": [
{
"row": 1,
"col": 1,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_06.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/detail_redirect\/2161"
},
{
"row": 1,
"col": 1,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_07.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/detail_redirect\/2171"
},
{
"row": 1,
"col": 1,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_08.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/detail_redirect\/2191"
},
{
"row": 1,
"col": 3,
"image_url": "\/sdcard\/Android\/data\/niubi\/files\/shop_item_09.png",
"category_goods_list": "https:\/\/niubi\/shop\/goods\/34\/category-list"
}
]
}
]
}
再看下加載的具體使用步驟：
1.在閃屏頁中 ： 復制assets目錄下的文件
new Thread(new Runnable() {
@Override
public void run() {
AssetCopyer assetCopyer = new AssetCopyer(SplashActivity.this,"assets.lst");
try {
assetCopyer.copy();
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
2.加載數據：
HttpKit.me().post(params, new JSONCallback<HomePageNew>() {
@Override
public void onError(ApiException e) {
super.onError(e);
loadErrorData();
}
@Override
public void onResponse(HomePageNew response) {
（sharedPreferences工具類)
StorageManager.getInstance().insert("homepage", mHomePageNew);//保存json數據到本地
...........更新頁面操作
...........
}
});
//加載錯誤的時候頁面展示
private void loadErrorData() {
if (mHomePageNew != null) {
return;
}
mHomePageNew = StorageManager.getInstance().query("homepage", HomePageNew.class);
if (mHomePageNew != null) {//如果獲取保存在本地的數據不為null，就使用保存在本地的數據
。。。。。。。。。。。。
} else {//第一次打開app無緩存并且無網的情況下，設置一個默認的數據 讀取json數據，展示
String jsonString = null;
try {
InputStream home_json_txt = AppKit.me.getAssets().open("rwh_home_data.json");
int available = home_json_txt.available();
byte[] bytes = new byte[available];
home_json_txt.read(bytes);
home_json_txt.close();
jsonString = new String(bytes).trim();
} catch (IOException e1) {
e1.printStackTrace();
}
if (jsonString != null) {
HomePageNew homePageNew = GsonKit.fromJson(jsonString, HomePageNew.class);
if (homePageNew != null) {
。。。。。。。。。。。//更新頁面操作
}
}
}
}
上面就基本完成了所要的需求。
