Before change：
public class Classroom {
private int class_id;
private String class_name;
private List<User> mUserList;
private List<Integer> rsc_tag_id;
public int getClass_id() {
return class_id;
}
public void setClass_id(int class_id) {
this.class_id = class_id;
}
public String getClass_name() {
return class_name;
}
public void setClass_name(String class_name) {
this.class_name = class_name;
}
public List<User> getUserList() {
return mUserList;
}
public void setUserList(List<User> userList) {
mUserList = userList;
}
public List<Integer> getRsc_tag_id() {
return rsc_tag_id;
}
public void setRsc_tag_id(List<Integer> rsc_tag_id) {
this.rsc_tag_id = rsc_tag_id;
}
}After Change：
public class Classroom {
private int class_id;
private String class_name;
public int getClass_id() {
return class_id;
}
public void setClass_id(int class_id) {
this.class_id = class_id;
}
public String getClass_name() {
return class_name;
}
public void setClass_name(String class_name) {
this.class_name = class_name;
}
}Tips：such changes may lead to some errors in other files, try to fix them！
Questions：why does class Image in Image.java have contribution String image_url?
In PlanetCategoryActivity.java：
- Where does the images come from？From back end!
- How to check if the invoke（调用） is success? Maybe is known now.
- How to due with the exception if database goes wrong? Retry or other method.
try to fix the code into following style：
const static int TEST = 1;
private static List<Image> images = Null;
if (Test)
{
images = initData();
}
else
{
/*
* download images by tag
* input: tag_id
* output: list<Image>
*/
}
public void initData()
{
List<Image> images = Null;
Image image = new Image(...)
//you can use image from baidu as test image!
...
return images
}Tips 1：Try to merge entity into activity and adapter
Tips 2：Implement Download Image from url for test
for reference：
public static Bitmap getBitmapFromUrl(final String url)
{
URL myFileUrl = null;
Bitmap bitmap = null;
try {
myFileUrl = new URL(url);
} catch (MalformedURLException e) {
e.printStackTrace();
}
try {
HttpURLConnection conn = (HttpURLConnection) myFileUrl
.openConnection();
conn.setDoInput(true);
conn.connect();
InputStream is = conn.getInputStream();
bitmap = BitmapFactory.decodeStream(is);
is.close();
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}Tips 3：How to get image url?
Step 1：find a image network：https://image.baidu.com
Step 2：search something like cats：https://image.baidu.com/search/index?tn=baiduimage&ipn=r&ct=201326592&cl=2&lm=-1&st=-1&fm=result&fr=&sf=1&fmq=1580973198457_R&pv=&ic=&nc=1&z=&hd=&latest=©right=&se=1&showtab=0&fb=0&width=&height=&face=0&istype=2&ie=utf-8&sid=&word=%E7%8C%AB
Step 4：press F12 or FN + F12 to find the html file of the website
Step 5：find <img id="..." ... src="..." ...> in the html file
Step 6：double click src to copy to url of the image：https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1581578052&di=cb4ccb9774c2128dc471fa78afb17dd1&imgtype=jpg&er=1&src=http%3A%2F%2Fn.sinaimg.cn%2Fsinacn15%2F275%2Fw640h435%2F20181010%2Fcaba-hkrzvkw4936632.jpg
Step 7：download the image into Bitmap using the code above
Advance Tip：try to minimize the total effort of revising your code if the requirement changes from downloading image from url into decoding images from a String（Something related to objected oriented analysis and design~）