javascript - 如何检查 goBack() 函数在 react 导航中是否可行？

Question

我有一个后退按钮，可以让用户返回一个屏幕，但是当没有屏幕可以返回时，我希望它做些别的事情，所以这是我的代码:

<Button onPress={()=>{
   if(CanGoBack){ // imaginary 'CanGoBack' variable
     this.props.navigation.goBack()
   }else{
     this.doSomething()
   }
}}/>

我怎样才能做到这一点？

Answer 1

Note this answer was originally written for react-navigation v3.3.0. You should check the current documentation for react-navigation to make sure that this is still supported and if there are any changes/easier methods.

React-Navigation v3

this.props.navigation 中有一个名为dangerouslyGetParent 的函数。

它在 documentation 中陈述了以下内容:

Another good use case for this is to find the index of the activeroute in the parent's route list. So in the case of a stack if you areat index 0 then you may not want to render a back button, but ifyou're somewhere else in the list then you would render a back button.

所以我们可以使用下面的方法来获取路由的索引

this.props.navigation.dangerouslyGetParent().state.index

所以我们可以在您的 Button 的 onPress 中使用它以下列方式检查我们是否回到了路线的起点。

<Button onPress={() => {
  // get the index of the route
  let index = this.props.navigation.dangerouslyGetParent().state.index;
  // handle the index we get
  if (index > 0) {
    this.props.navigation.goBack();
  } else {
    this.doSomething();
  }
}}/>

---

React-Navigation v5 更新

来自documentation ，我们可以看到 dangerouslyGetParent 仍然存在。

This method returns the navigation prop from the parent navigator thatthe current navigator is nested in. For example, if you have a stacknavigator and a tab navigator nested inside the stack, then you canuse dangerouslyGetParent inside a screen of the tab navigator to getthe navigation prop passed from the stack navigator.

所以可以在v5中对v3使用上述方法。

---

v5 中的 canGoBack()

还有一个未记录的 api，称为 canGoBack()。这可以通过以下方式从导航 Prop 访问:

this.props.navigation.canGoBack()

如果您能够返回堆栈，此属性将返回一个 bool 值。这意味着我们可以通过以下方式更新我们为 v3 所做的代码。

<Button onPress={() => {
  // check to see if it is possible to go back
  let canGoBack = this.props.navigation.canGoBack();
  // handle what we do it we can/cannot go back
  if (canGoBack) {
    this.props.navigation.goBack();
  } else {
    this.doSomething();
  }
}}/>

但是，由于这是一个未记录的 API，它很可能会更改，因此依赖它可能会有风险。

---

v6 中的 canGoBack()

现在看来 canGoBack 已经记录在案了，您可以找到信息 here

This method returns a boolean indicating whether there's any navigation history available in the current navigator, or in any parent navigators. You can use this to check if you can call navigation.goBack():

if (navigation.canGoBack()) {
  navigation.goBack();
}

Don't use this method for rendering content as this will not trigger a re-render. This is only intended for use inside callbacks, event listeners etc.