2.8.1. Conditional judgment ¶
v-if ¶
The conditional judgment uses the v-if instruction, and the expression of the instruction will only be displayed when it returns true :
v-if instruction ¶
Use in an element v-if directive:
<divid="app"><pv-if="seen">Now you see mep>div><script>const app = {
data() { return { seen: true /\* Change to false, the information cannot be displayed \*/ } } }
Vue.createApp(app).mount('#app')script>
Here, the v-if instruction will determine whether to insert the p element based on the value of the expression seen ( true or false ).
Because v-if is an instruction, it must be added to an element. If there are multiple elements, they can be wrapped around the element, the final rendering result will not contain any elements. And use v-if on top. The final rendering result will not include the element. v-if instruction ¶
In element using the v-if directive: <divid="app"><templatev-if="seen"><h1>websiteh1><p>Googlep><p>Runoobp><p>Taobaop>template>div><script>const
app = { data() { return { seen: true /\* Change to false, the information cannot be displayed \*/ }
} } Vue.createApp(app).mount('#app')script>
v-else ¶
You can use the v-else instruction to add an “else” block to the v-if :
v-else instruction ¶
Randomly generate a number, determine whether it is greater than 0.5, and then output the corresponding information:
<divid="app"><divv-if="Math.random() > 0.5">Random number greater than
0.5div><divv-else>Random number less than or equal to
0.5div>div><script>Vue.createApp(app).mount('#app')script>
v-else-if ¶
v-else-if that is, v-if of else-if block, which can be used many times in chain:
v-else instruction ¶
Determine the value of the variable type :
<divid="app"><divv-if="type === 'A'">Adiv><divv-else-if="type ===
'B'">Btype === 'C'">CNot
A/B/Cdiv>div><script>const app = { data() { return { type: "C" } } }
Vue.createApp(app).mount('#app')script>
</div>
<p>
<code class="docutils literal notranslate">
<span class="pre">
v-else
</span>
</code>
、
<code class="docutils literal notranslate">
<span class="pre">
v-else-if
</span>
</code>
have to follow.
<code class="docutils literal notranslate">
<span class="pre">
v-if
</span>
</code>
or
<code class="docutils literal notranslate">
<span class="pre">
v-else-if
</span>
</code>
After that.
</p>
v-show ¶
We can also use v-show directive to display elements according to conditions:
v-show instruction ¶
Hello!
-
1. Geographical Information Systems in the World Wide Web Era
4
-
2. Basic technology of WebGIS
4
-
3. Geographic Web Services
5
-
4. aggregation of geographical information
4
-
5. mobile GIS
5
-
6. Geographic information portal
3
-
7. New generation national spatial data infrastructure and GIS
4
-
8. Application of WebGIS in E-Commerce
3
-
9. Application of WebGIS in E-government
3
-
10. Hotspots and frontiers of WebGIS
2
-
1. Angularjs2
8
-
1. SVG tutorial
19
-
1. Memcached
20
-
1. C# tutorial
61
-
1. Sqlite
47
-
2. Go
43
-
2. Docker
59
-
2. Vue3
19
-
2. Servlet
21
-
3. React
23
-
3. SOAP tutorial
10
-
3. Android
18
-
3. Mongodb
44
-
3. Kotlin
18
-
4. Lua
31
-
4. MySQL tutorial
34
-
4. Appml
12
-
5. Perl
45
-
5. Postgresql
41
-
web
15
-
5. Web Services tutorial
6
-
6. Ruby
41
-
6. Design-pattern
35
-
7. Django
18
-
7. Rust
22
-
6. WSDL tutorial
8
-
8. Foundation
39
-
9. Ios
43
-
8. Css3
26
-
9. Swift
43
-
11. HTML tutorial-(HTML5 Standard)
54
-
12. Http
6
-
13. Regex
6
-
14. Regexp
7
Principles, Technologies, and Methods of Geographic Information Systems
102
In recent years, Geographic Information Systems (GIS) have undergone rapid development in both theoretical and practical dimensions. GIS has been widely applied for modeling and decision-making support across various fields such as urban management, regional planning, and environmental remediation, establishing geographic information as a vital component of the information era. The introduction of the “Digital Earth” concept has further accelerated the advancement of GIS, which serves as its technical foundation. Concurrently, scholars have been dedicated to theoretical research in areas like spatial cognition, spatial data uncertainty, and the formalization of spatial relationships. This reflects the dual nature of GIS as both an applied technology and an academic discipline, with the two aspects forming a mutually reinforcing cycle of progress.
-
1. Introduction to Geographic Information Systems
6
-
2. From the Real World to the Bit World
3
-
3. Spatial Data Model
7
-
4. Spatial Reference Systems and Map Projections
5
-
5. Data in GIS
4
-
6. Spatial data acquisition
2
-
7. Spatial Data Management
6
-
8. Spatial analysis
8
-
9. Digital Terrain Model (DTM) and Terrain Analysis
5
-
10. Spatial modeling and spatial decision support
6
-
11. Spatial data representation and map making
6
-
12. 3S Integration Technology
5
-
13. Network Geographic Information System
4
-
14. Examples of Geographic Information System Application
8
-
15. Organization and Management of Geographic Information System Application Projects
10
-
16. Geographic Information system Software Engineering Technology
7
-
17. Geographic Information System Standards
3
-
18. Geographic Information System and Society
3
-
19. Earth Information Science and Digital Earth
4