图片缓存支持。

src/www/js/cache.js

@@ -0,0 +1,58 @@
+blackberry.io.sandbox = false;
+var cache = {
+    get: function(url, strdate, callback) {
+        /*
+         * url : 图片网址
+         * strdate : 当前日期
+         * callback(string) ：回调，返回本地地址或者网址。
+         */
+        if (this.isExisted(strdate)){
+            callback(this.buildfileurl(strdate));
+            return;
+        }
+        /*
+         * 缓存中不存在，开始下载
+         */
+        console.log("downloading " + url);
+        try {
+            blackberry.io.filetransfer.download(
+                    url,
+                    this.buildurl(strdate),
+                    function(result) {
+                        console.log("file downloaded,fullPath: " + result.fullPath);
+                        callback("file://" + result.fullPath);
+                    },
+                    function(result) {
+                        console.log("Download failed");
+                        console.log("Error code: " + result.code);
+                        console.log("HTTP status: " + result.http_status);
+                        console.log("Source: " + result.source);
+                        console.log("Target: " + result.target);
+                        callback(url);
+                    });
+        }
+        catch (e) {
+            console.log(e);
+            callback(url);
+        }
+    },
+    isExisted: function(strdate) {
+        /*
+         * 确定是否已缓存
+         */
+        var url = this.buildfileurl(strdate);
+        console.log("Checking: " + url);
+        var http = new XMLHttpRequest();
+        http.open('HEAD', url, false);
+        http.send(null);
+        console.log(http.status);
+        if (http.status == 0) return false;
+        return true;
+    },
+    buildurl: function(str) {
+        return blackberry.io.home + "/" + str + ".jpg";
+    },
+    buildfileurl: function(str) {
+        return "file://" + this.buildurl(str);
+    }
+};