Detailed introduction to UniApp's background requests

UniApp is a cross-platform development framework based on Vue.js, which supports the development of iOS, Android and Web applications using the same set of code. In UniApp, we can use AJAX requests to communicate with the backend server to obtain or submit data. In this article, we will introduce UniApp’s background requests in detail.

In UniApp, we use uni.request or uni.uploadFile to initiate an HTTP network request. The uni.request method is used for ordinary requests, while the uni.uploadFile method is used for uploading files.

First, let’s take a look at how to use the uni.request method. This method will return a Promise object, and we can use chain calls to handle the request.

uni.request({
    url: 'http://www.example.com/api',
    data: {
        name: '小明',
        age: 18
    },
    method: 'POST',
    header: {
        'content-type': 'application/json'
    }
}).then(res => {
    console.log(res.data);
}).catch(err => {
    console.error(err);
});

In the above code, we request a data from the server. We used the POST method to pass in data in JSON format. Next, we set the request headers to tell the server that we are using data in JSON format. Finally, we use Promise-based asynchronous operations to process the server's response.

Now, let’s take a look at how to upload a file to the server using the uni.uploadFile method.

uni.chooseImage({
    success: function (res) {
        uni.uploadFile({
            url: 'http://www.example.com/upload',
            filePath: res.tempFilePaths[0],
            name: 'file',
            formData: {
                'user': '小明'
            },
            success: function (uploadRes) {
                console.log(uploadRes);
            },
            fail: function (err) {
                console.error(err);
            }
        });
    }
});

In the above code, we used the uni.chooseImage method to select a picture from the album or camera. Next, we use the uni.uploadFile method to upload this image. In this request, we pass in three parameters: the path to the file, the name of the file, and the form data. Finally, we process the server's response.

Of course, there are some other options and configurations that can be achieved through configuration. These options and configurations include:

1. url: the requested server URL;
2. method: the request method used;
3. data: Requested data;
4. header: Requested message header;
5. dataType: Response Data type;
6. timeout: request timeout;
7. sslVerify: SSL certificate verification;
8. success: The callback function when the request is successful;
9. fail: The callback function when the request fails;
10. complete: The callback when the request ends Function;
11. formData: form data when uploading a file;
12. name: field name when uploading a file;
13. filePath: Uploaded file path;
14. timeout: Upload timeout.

In the above options and configurations, url, method, data, header, success and fail are required, the others are optional.

When we need to request data from the background, we can also use the higher-level API of uni.request: uni.request.toPromise and uni.requestAll.toPromise. These APIs are Promise-based asynchronous calls, which provide better control over asynchronous code flow and error handling.

To summarize, UniApp can easily use the uni.request method and the uni.uploadFile method to make network requests and file uploads. We can handle the server's response by configuring request options and using callback functions. Of course, we can also use higher-level APIs, such as uni.request.toPromise and uni.requestAll.toPromise, to better control the flow and error handling of asynchronous code.

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