1# UIAbility Launch Type
2
3
4The launch type of the [UIAbility](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md) component refers to the state of the UIAbility instance at startup. Three launch types are available:
5
6
7- [Singleton](#singleton)
8
9- [Multiton](#multiton)
10
11- [Specified](#specified)
12
13
14## Singleton
15
16**singleton** is the default launch type.
17
18Each time [startAbility()](../reference/apis-ability-kit/js-apis-inner-application-uiAbilityContext.md#uiabilitycontextstartability) is called, if a [UIAbility](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md) instance of this type already exists in the application process, the instance is reused. In other words, UIAbility of this type can have only one instance in the system, meaning that only one mission is displayed in the system application Recents.
19
20**Figure 1** Demonstration effect in singleton mode
21
22![uiability-launch-type1](figures/uiability-launch-type1.gif)  
23
24> **NOTE**
25>
26> If [startAbility()](../reference/apis-ability-kit/js-apis-inner-application-uiAbilityContext.md#uiabilitycontextstartability) is called to start an existing UIAbility instance in singleton mode, that instance is started, and no new UIAbility instance is created. In this case, the [onNewWant()](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md#uiabilityonnewwant) callback is invoked, but the [onCreate()](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md#uiabilityoncreate) and [onWindowStageCreate()](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md#uiabilityonwindowstagecreate) callbacks are not.
27
28To use the singleton mode, set **launchType** in the [module.json5 file](../quick-start/module-configuration-file.md) to **singleton**.
29
30
31```json
32{
33  "module": {
34    // ...
35    "abilities": [
36      {
37        "launchType": "singleton",
38        // ...
39      }
40    ]
41  }
42}
43```
44
45
46## Multiton
47
48In multiton mode, each time [startAbility()](../reference/apis-ability-kit/js-apis-inner-application-uiAbilityContext.md#uiabilitycontextstartability) is called, a new [UIAbility](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md) instance is created in the application process. Multiple missions are displayed for UIAbility of this type in Recents.
49
50**Figure 2** Demonstration effect in multiton mode
51
52![uiability-launch-type2](figures/uiability-launch-type2.gif)  
53
54To use the multiton mode, set **launchType** in the [module.json5 file](../quick-start/module-configuration-file.md) to **multiton**.
55
56
57```json
58{
59  "module": {
60    // ...
61    "abilities": [
62      {
63        "launchType": "multiton",
64        // ...
65      }
66    ]
67  }
68}
69```
70
71
72## Specified
73
74The **specified** mode is used in some special scenarios. For example, in a document application, you may want a document instance to be created each time you create a document, and you may also want to use the same document instance when you open an existing document.
75
76**Figure 3** Demonstration effect in specified mode
77
78![uiability-launch-type3](figures/uiability-launch-type3.gif)  
79
80In the following example, there are two [UIAbility](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md) components: EntryAbility and SpecifiedAbility (with the launch type **specified**). To start SpecifiedAbility from EntryAbility, proceed as follows:
81
821. In SpecifiedAbility, set **launchType** in the [module.json5 file](../quick-start/module-configuration-file.md) to **specified**.
83
84   ```json
85   {
86     "module": {
87       // ...
88       "abilities": [
89         {
90           "launchType": "specified",
91           // ...
92         }
93       ]
94     }
95   }
96   ```
97
982. Create a unique string key for the SpecifiedAbility instance. Each time [startAbility()](../reference/apis-ability-kit/js-apis-inner-application-uiAbilityContext.md#uiabilitycontextstartability) is called, the application, based on the key, identifies the UIAbility instance used to respond to the request. In EntryAbility, add a custom parameter, for example, **instanceKey**, to the [want](../reference/apis-ability-kit/js-apis-app-ability-want.md) parameter in [startAbility()](../reference/apis-ability-kit/js-apis-inner-application-uiAbilityContext.md#uiabilitycontextstartability) to distinguish the UIAbility instances.
99
100   ```ts
101    // Configure a unique key for each UIAbility instance.
102    // For example, in the document usage scenario, use the document path as the key.
103    import { common, Want } from '@kit.AbilityKit';
104    import { hilog } from '@kit.PerformanceAnalysisKit';
105    import { BusinessError } from '@kit.BasicServicesKit';
106
107    const TAG: string = '[Page_StartModel]';
108    const DOMAIN_NUMBER: number = 0xFF00;
109
110    function getInstance(): string {
111      return 'KEY';
112    }
113
114    @Entry
115    @Component
116    struct Page_StartModel {
117      private KEY_NEW = 'KEY';
118
119      build() {
120        Row() {
121          Column() {
122            // ...
123            Button()// ...
124              .onClick(() => {
125                let context: common.UIAbilityContext = getContext(this) as common.UIAbilityContext;
126                // context is the UIAbilityContext of the initiator UIAbility.
127                let want: Want = {
128                  deviceId: '', // An empty deviceId indicates the local device.
129                  bundleName: 'com.samples.stagemodelabilitydevelop',
130                  abilityName: 'SpecifiedFirstAbility',
131                  moduleName: 'entry', // moduleName is optional.
132                  parameters: {
133                    // Custom information.
134                    instanceKey: this.KEY_NEW
135                  }
136                };
137                context.startAbility(want).then(() => {
138                  hilog.info(DOMAIN_NUMBER, TAG, 'Succeeded in starting SpecifiedAbility.');
139                }).catch((err: BusinessError) => {
140                  hilog.error(DOMAIN_NUMBER, TAG, `Failed to start SpecifiedAbility. Code is ${err.code}, message is ${err.message}`);
141                })
142                this.KEY_NEW = this.KEY_NEW + 'a';
143              })
144            // ...
145            Button()// ...
146              .onClick(() => {
147                let context: common.UIAbilityContext = getContext(this) as common.UIAbilityContext;
148                // context is the UIAbilityContext of the initiator UIAbility.
149                let want: Want = {
150                  deviceId: '', // An empty deviceId indicates the local device.
151                  bundleName: 'com.samples.stagemodelabilitydevelop',
152                  abilityName: 'SpecifiedSecondAbility',
153                  moduleName: 'entry', // moduleName is optional.
154                  parameters: {
155                    // Custom information.
156                    instanceKey: getInstance()
157                  }
158                };
159                context.startAbility(want).then(() => {
160                  hilog.info(DOMAIN_NUMBER, TAG, 'Succeeded in starting SpecifiedAbility.');
161                }).catch((err: BusinessError) => {
162                  hilog.error(DOMAIN_NUMBER, TAG, `Failed to start SpecifiedAbility. Code is ${err.code}, message is ${err.message}`);
163                })
164                this.KEY_NEW = this.KEY_NEW + 'a';
165              })
166            // ...
167          }
168          .width('100%')
169        }
170        .height('100%')
171      }
172    }
173   ```
174   
1753. Before SpecifiedAbility is started, the [onAcceptWant()](../reference/apis-ability-kit/js-apis-app-ability-abilityStage.md#abilitystageonacceptwant) callback of the corresponding AbilityStage instance is invoked to obtain the key of the target [UIAbility](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md). If a UIAbility instance matching the key exists, the system starts the UIAbility instance and invokes its [onNewWant()](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md#uiabilityonnewwant) callback. Otherwise, the system creates a new UIAbility instance and invokes its [onCreate()](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md#uiabilityoncreate) and [onWindowStageCreate()](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md#uiabilityonwindowstagecreate) callbacks.
176
177   In the sample code, the [onAcceptWant()](../reference/apis-ability-kit/js-apis-app-ability-abilityStage.md#abilitystageonacceptwant) callback uses the passed [want](../reference/apis-ability-kit/js-apis-app-ability-want.md) parameter to obtain the custom parameter **instanceKey**. The service logic returns a key string based on the **instanceKey** parameter to identify the UIAbility instance. If the returned key maps to a started UIAbility instance, the system pulls the UIAbility instance back to the foreground and gives it the focus. If the returned key does not map to a started UIAbility instance, the system creates a new UIAbility instance and starts it.
178
179   ```ts
180    import { AbilityStage, Want } from '@kit.AbilityKit';
181
182    export default class MyAbilityStage extends AbilityStage {
183      onAcceptWant(want: Want): string {
184        // In the AbilityStage instance of the callee, a key string corresponding to a UIAbility instance is returned for UIAbility whose launch type is specified.
185        // In this example, SpecifiedAbility of module1 is returned.
186        if (want.abilityName === 'SpecifiedFirstAbility' || want.abilityName === 'SpecifiedSecondAbility') {
187          // The returned key string is a custom string.
188          if (want.parameters) {
189            return `SpecifiedAbilityInstance_${want.parameters.instanceKey}`;
190          }
191        }
192        // ...
193        return 'MyAbilityStage';
194      }
195    }
196   ```
197
198   > **NOTE**
199   >
200   > - If [startAbility()](../reference/apis-ability-kit/js-apis-inner-application-uiAbilityContext.md#uiabilitycontextstartability) is called to start an existing UIAbility instance in specified mode, and the [onAcceptWant()](../reference/apis-ability-kit/js-apis-app-ability-abilityStage.md#abilitystageonacceptwant) callback of [AbilityStage](../reference/apis-ability-kit/js-apis-app-ability-abilityStage.md) matches that UIAbility instance, that instance is started, and no new UIAbility instance is created. In this case, the **onNewWant()** callback is invoked, but the **onCreate()** and **onWindowStageCreate()** callbacks are not.
201   >
202   > - AbilityStage is not automatically generated by default in the project of DevEco Studio. For details about how to create an AbilityStage file, see [AbilityStage Component Container](abilitystage.md).
203
204For example, in the document application, different keys are bound to different document instances. Each time a document is created, a new key (for example, file path) is passed in, and a new [UIAbility](../reference/apis-ability-kit/js-apis-app-ability-uiAbility.md) instance is created when the UIAbility is started in [AbilityStage](../reference/apis-ability-kit/js-apis-app-ability-abilityStage.md). However, when an existing document is opened, the same UIAbility instance is started again in AbilityStage.
205
206The following steps are used as an example.
207
208   1. Open file A. A UIAbility instance, UIAbility instance 1, is started.
209   2. Close the process of file A in Recents. UIAbility instance 1 is destroyed. Return to the home screen and open file A again. A new UIAbility instance, UIAbility instance 2, is started.
210   3. Return to the home screen and open file B. A new UIAbility instance, UIAbility instance 3, is started.
211   4. Return to the home screen and open file A again. UIAbility instance 2 is started. This is because the system automatically matches the key with the UIAbility instance and starts the UIAbility instance that has a matching key. In this example, UIAbility instance 2 has the same key as file A. Therefore, the system pulls back UIAbility instance 2 and focuses it without creating a new instance.
212