等待映射内的所有异步函数完成执行

Question

我想在映射内完成所有异步函数的执行，然后更改组件的状态。我给你留了一个减少的代码部分，以防你能帮助我。我所要做的就是在每次用户取消时显示我自己的权限屏幕。为了简化，我有这个：const permissions = {    cameraRoll: {        iconType: "ionicon",        iconName: "ios-images",        title: "Enable camera roll",        subtitle:          "To upload content from your Gallery, you have to granted the camera roll permission",        buttonText: "Enable camera roll",        checkPermission: checkCameraRollPermission,        requirePermission: requireCameraRollPermission,      },    };}const checkCameraRollPermission = async () => {    const { status, canAskAgain } = await Permissions.getAsync(      Permissions.CAMERA_ROLL    );    return { status, canAskAgain };  };  const requireCameraRollPermission = async () => {    const { status, canAskAgain } = await Permissions.askAsync(      Permissions.CAMERA_ROLL    );    return { status, canAskAgain };  };/* I HAVE TO WAIT FOR ALL THE FUNCTIONS TO FINISH EXECUTIONFOR EACH OBJECT ON THE MAP BUT THIS IS NOT WORKING :( */getMissingPermissions = () => {    // Only check permissions on the foreground    if (AppState.currentState.match(/active/)) {      // We have to empty the current missing permssions and recalculate them      const permissionsArray = [];      Promise.all(        Object.keys(permissions).map((key) => {          permissions[key].checkPermission().then(({ status }) => {            if (status !== "granted") {              permissionsArray.push(permissions[key]);            }          });        })      ).then(() => {        this.setState({          missingPermissions: permissionsArray,        });      });    }  };有什么想法吗？谢谢

Answer 1

您需要以数组的形式提供承诺。目前，您没有从地图中返回任何内容，这是导致问题的原因。Promise.all

此外，代替使用 permissionsArray 变量，您可以简单地从嵌套 promise 中返回所需的值，该值将在响应中可用Promise.all(...).then(...)

getMissingPermissions = () => {

    // Only check permissions on the foreground

    if (AppState.currentState.match(/active/)) {

      // We have to empty the current missing permssions and recalculate them

      Promise.all(

        Object.keys(permissions).map((key) => {

          return permissions[key].checkPermission().then(({ status }) => {

            if (status !== "granted") {

              return permissions[key];

            }

            return;

          });

        })

      ).then((res) => {

        const permissionsArray = res.filter(Boolean)// Filter out undefined values

        this.setState({

          missingPermissions: permissionsArray,

        });

      });

    }

  };