java - Android-应该在未运行任务的情况下

我正在使用Backendless存储我的应用程序用户的数据。 Backendless仅可以选择使您的电子邮件或用户名唯一。我将用户名字段设置为唯一，这就是用户将用于登录的字段。可以重复使用电子邮件，因此我在注册之前制定了一种方法来检查电子邮件是否存在。

这是createUser方法，它开始启动并立即调用该方法以检查电子邮件的可用性：

private void createUser() {
    showProgressDialog();

    if (isEmailAvailable(inputEmail.getText().toString().trim())) {
        BackendlessUser user = new BackendlessUser();
        user.setProperty(BackendSettings.USERNAME_KEY, inputUsername.getText().toString().trim());
        user.setEmail(inputEmail.getText().toString().trim());
        user.setPassword(inputPassword.getText().toString());

        Backendless.UserService.register(user, new AsyncCallback<BackendlessUser>() {
            @Override
            public void handleResponse(BackendlessUser backendlessUser) {
                hideProgressDialog();
                Toast.makeText(CreateAccountActivity.this, BackendSettings.REGISTER_SUCCESS_MESSAGE, Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(CreateAccountActivity.this, MainActivity.class);
                startActivity(intent);
                finish();
            }

            @Override
            public void handleFault(BackendlessFault backendlessFault) {
                hideProgressDialog();
                String errorCode = backendlessFault.getCode();
                String errorMessage;
                switch (errorCode) {
                    case "3040":
                        errorMessage = BackendSettings.ERROR_3040;
                        break;
                    case "3033":
                        errorMessage = BackendSettings.ERROR_3033;
                        break;
                    default:
                        errorMessage = "An unknown error occurred. Try again.";
                }
                Toast.makeText(CreateAccountActivity.this, errorMessage, Toast.LENGTH_SHORT).show();
            }
        });
    } else {
        hideProgressDialog();
        Toast.makeText(CreateAccountActivity.this, BackendSettings.ERROR_EMAIL_TAKEN, Toast.LENGTH_SHORT).show();
    }
}

这是检查电子邮件可用性的方法：

private boolean isAvailable;
private boolean isEmailAvailable(String email) {
    isAvailable = false;

    String whereClause = "email = '" + email + "'";
    BackendlessDataQuery dataQuery = new BackendlessDataQuery();
    dataQuery.setWhereClause(whereClause);
    Backendless.Persistence.of(BackendlessUser.class).find(dataQuery, new AsyncCallback<BackendlessCollection<BackendlessUser>>() {
        @Override
        public void handleResponse(BackendlessCollection<BackendlessUser> userBackendlessCollection) {
            isAvailable = userBackendlessCollection.getData().isEmpty();
        }

        @Override
        public void handleFault(BackendlessFault backendlessFault) {
            Toast.makeText(CreateAccountActivity.this, backendlessFault.getMessage(), Toast.LENGTH_SHORT).show();
        }
    });
    return isAvailable;
}

好的，所以我总是收到这样的消息，即该电子邮件已经被接收，即使没有被接收。因此，我决定将Toast消息放入handleResponse的isEmailAvailble方法中。如果电子邮件可用，我将其打印出来。因此，我首先从createUser的else子句中获得了消息，说该电子邮件已经被接收，然后从isEmailAvailable方法中获得了该消息。似乎此后正在运行isEmailAvailable方法。我不确定这是怎么回事。

最佳答案

哇！
错误在isEmailAvailable方法中。

查找是否为异步方法。
它的工作方式是这样的：您调用它，它开始工作并立即返回，直到实际产生任何结果为止。
稍后，它将调用回调方法。所以，当你这样做

    return isAvailable;

在该行上，isAvailable始终为false，因为它仍未更改。

您应该做一些异步工作。
1.调用Backendless.Persistence.of（BackendlessUser.class）.find（...）
2.等待答案。您只会知道结果

   public void handleResponse(BackendlessCollection<BackendlessUser> userBackendlessCollection) {
       isAvailable = userBackendlessCollection.getData().isEmpty();
   }

3.刚做完剩下的工作

    isAvailable = userBackendlessCollection.getData().isEmpty();

创建方法doCreateUser，将您的“ if”主体放入其中，并在isAvailable = userBackendlessCollection.getData（）。isEmpty（）;之后从handleResponse调用它。

使用此代码：

    private void createUser() {
        showProgressDialog();
        checkEmailAvailable(inputEmail.getText().toString().trim());
    }

    private void checkEmailAvailable(String email) {
        String whereClause = "email = '" + email + "'";
        BackendlessDataQuery dataQuery = new BackendlessDataQuery();
        dataQuery.setWhereClause(whereClause);
        Backendless.Persistence.of(BackendlessUser.class).find(dataQuery, new AsyncCallback<BackendlessCollection<BackendlessUser>>() {
            @Override
            public void handleResponse(BackendlessCollection<BackendlessUser> userBackendlessCollection) {
                isAvailable = userBackendlessCollection.getData().isEmpty();
                if (isAvailable){
                    doCreateuser();
                } else {
                    hideProgressDialog();
                    Toast.makeText(CreateAccountActivity.this, BackendSettings.ERROR_EMAIL_TAKEN, Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void handleFault(BackendlessFault backendlessFault) {
                Toast.makeText(CreateAccountActivity.this, backendlessFault.getMessage(), Toast.LENGTH_SHORT).show();
                hideProgressDialog();
            }
        });
    }

    private void doCreateuser(){
        BackendlessUser user = new BackendlessUser();
        user.setProperty(BackendSettings.USERNAME_KEY, inputUsername.getText().toString().trim());
        user.setEmail(inputEmail.getText().toString().trim());
        user.setPassword(inputPassword.getText().toString());

        Backendless.UserService.register(user, new AsyncCallback<BackendlessUser>() {
            @Override
            public void handleResponse(BackendlessUser backendlessUser) {
                hideProgressDialog();
                Toast.makeText(CreateAccountActivity.this, BackendSettings.REGISTER_SUCCESS_MESSAGE, Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(CreateAccountActivity.this, MainActivity.class);
                startActivity(intent);
                finish();
            }

            @Override
            public void handleFault(BackendlessFault backendlessFault) {
                hideProgressDialog();
                String errorCode = backendlessFault.getCode();
                String errorMessage;
                switch (errorCode) {
                    case "3040":
                        errorMessage = BackendSettings.ERROR_3040;
                        break;
                    case "3033":
                        errorMessage = BackendSettings.ERROR_3033;
                        break;
                    default:
                        errorMessage = "An unknown error occurred. Try again.";
                }
                Toast.makeText(CreateAccountActivity.this, errorMessage, Toast.LENGTH_SHORT).show();
            }
        });
    }

关于java - Android-应该在未运行任务的情况下，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/38024161/