android - 找不到值时，Android应用程序崩溃

Question

我正在尝试从Yahoo!获取货币值!使用Yahoo!融资API进入我的Android应用。

但是对于某些货币，找不到任何值，这会导致我的应用崩溃。

如果找不到任何值，则应显示错误。

String s;
String exResult = "";
final String val[];
val  = getResources().getStringArray(R.array.value);
try {
    s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22" + val[from] + val[to] + "%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");
    JSONObject jObj;
    jObj = new JSONObject(s);
    exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");

    System.out.println(exResult);
} catch (JSONException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (ClientProtocolException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}
return exResult;

Answer 1

可能是因为使用了getString()方法，
仅在解析optString()方法而不是getString()时使用

.getString(“Rate”); -> .optString(“Rate”);

 /**
     * Returns the value mapped by {@code name} if it exists, coercing it if
     * necessary, or throws if no such mapping exists.
     *
     * @throws JSONException if no such mapping exists.
     */
    public String getString(String name) throws JSONException {
        Object object = get(name);
        String result = JSON.toString(object);
        if (result == null) {
            throw JSON.typeMismatch(name, object, "String");
        }
        return result;
    }

    /**
     * Returns the value mapped by {@code name} if it exists, coercing it if
     * necessary, or the empty string if no such mapping exists.
     */
    public String optString(String name) {
        return optString(name, "");
    }