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同步截击请求锁定

synchronous android-volley android

leonheess · 技术社区 · 7 年前

我正在尝试实现“实时”输入验证。我现在面临的问题是如何实时检查数据库中是否已经存在用户名。

对于所有的数据库请求,我都使用截击发布到PHP API,结果是:

private boolean checkTaken(String username, Context context){
    boolean taken;
    Volley.getInstance(context).addToRequestQueue(new StringRequest(Request.Method.POST, url, output -> taken = output.contains("taken"), error -> {}) {
        @Override
        protected Map<String, String> getParams() {
            Map<String, String> params = new HashMap<>();
            params.put("username", username);
            return params;
        }
        @Override
        public Map<String, String> getHeaders() {
            Map<String, String> params = new HashMap<>();
            params.put("Content-Type", "application/x-www-form-urlencoded");
            return params;
        }
    });
    return taken;
}

这很好,但不起作用,因为返回语句在API响应到达之前很久就到达了。就在那时,我发现了RequestFutures,并试图按照我所看到的实现它们 here

 private boolean checkTaken(String username, Context context){

    RequestFuture<String> taken = RequestFuture.newFuture();

    Volley.getInstance(context).addToRequestQueue(new StringRequest(Request.Method.POST, url, taken, error -> {}) {
        @Override
        protected Map<String, String> getParams() {
            Map<String, String> params = new HashMap<>();
            params.put("username", username);
            return params;
        }
        @Override
        public Map<String, String> getHeaders() {
            Map<String, String> params = new HashMap<>();
            params.put("Content-Type", "application/x-www-form-urlencoded");
            return params;
        }
    });
    try {
        return taken.get(500, TimeUnit.MILLISECONDS).contains("taken");
    } catch (InterruptedException | ExecutionException | TimeoutException e) {
        return false;
    }
}

不幸的是,即使我将超时增加到无法忍受的程度,它也无法工作 taken.get() 永远无法解决。我想是因为 taken

我将非常感谢你给我一个提示,为什么这不起作用,或者给我的问题提供另一个解决方案。

方法调用:

if (!email.matches(regex)){
    return "Username has an invalid format";
} else if (checkTaken(username, context)){
    return "Username already taken";
} else{
    return null;
}

1 回复 | 直到 7 年前

nasch 7 年前

private void checkTaken(String username, Context context, Callback callback){
    boolean taken;
    Volley.getInstance(context).addToRequestQueue(new StringRequest(Request.Method.POST, url, 
        output -> callback.done(output.contains("taken")), 
        error -> {
           // TODO handle this error
        }) {
        @Override
        protected Map<String, String> getParams() {
            Map<String, String> params = new HashMap<>();
            params.put("username", username);
            return params;
        }
        @Override
        public Map<String, String> getHeaders() {
            Map<String, String> params = new HashMap<>();
            params.put("Content-Type", "application/x-www-form-urlencoded");
            return params;
        }
    });
}

定义回调接口并从调用的任何位置传入lambda表达式 checkTaken :

// This method wherever this is defined also needs to accept a callback so it can be asynchronous
public void whatever(StringCallback callback) {
    // ...
    if (!email.matches(regex)){
        callback.done("Username has an invalid format");
    } else {
        checkTaken(username, context, taken -> 
                 callback.done(taken ? "Username already taken" : null));
    }

whatever(error -> {
    if(error == null) {
        handleSuccess();
    }
    else {
        handleError(error);
    }
 );