如何将相册选择的图片生成PixelMap
====================

*   方法一：
    
    1.  创建图库选择器实例，调用select()接口拉起photoPicker界面选择图片。选择成功后，返回PhotoSelectResult结果集。
    2.  通过photoAccessHelper模块的getAssets接口获取媒体文件的URI。
    3.  调用getThumbnail获取缩略图。
    
    参考代码如下：
    
    import { photoAccessHelper } from '@kit.MediaLibraryKit';
    import { BusinessError } from '@kit.BasicServicesKit';
    import { dataSharePredicates } from '@kit.ArkData';
    import { common } from '@kit.AbilityKit';
    
    const context = AppStorage.get("context") as common.UIAbilityContext;
    @Entry
    @Component
    struct WebComponent {
      build() {
        Column() {
          Button('选择图片').onClick(() => {
            try {
              let uris: Array<string> = \[\];
              let PhotoSelectOptions = new photoAccessHelper.PhotoSelectOptions();
              PhotoSelectOptions.MIMEType = photoAccessHelper.PhotoViewMIMETypes.IMAGE\_TYPE;
              PhotoSelectOptions.maxSelectNumber = 1;
              let photoPicker = new photoAccessHelper.PhotoViewPicker();
              photoPicker.select(PhotoSelectOptions).then((PhotoSelectResult: photoAccessHelper.PhotoSelectResult) => {
                console.info('photoPicker.select successfully, PhotoSelectResult uri: ' + JSON.stringify(PhotoSelectResult));
                uris = PhotoSelectResult.photoUris;
                let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(context);
                let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates();
               _ // Configure query conditions, use PhotoViewPicker to select the URI of the image to be queried_
                predicates.equalTo('uri', uris\[0\]);
                let fetchOptions: photoAccessHelper.FetchOptions = {
                  fetchColumns: \[\],
                  predicates: predicates
                };
                phAccessHelper.getAssets(fetchOptions, async (err, fetchResult) => {
                  if (fetchResult !== undefined) {
                    console.info('fetchResult success');
                    let photoAsset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject();
                    if (photoAsset !== undefined) {
                    _  // Get Thumbnail_
                      photoAsset.getThumbnail((err, pixelMap) => {
                        if (err == undefined) {
                          console.info('getThumbnail successful ' + JSON.stringify(pixelMap));
                        } else {
                          console.error('getThumbnail fail', err);
                        }
                      });
                      console.info('photoAsset.displayName : ' + photoAsset.displayName);
                    }
                  } else {
                    console.error(\`fetchResult fail with error: ${err.code}, ${err.message}\`);
                  }
                });
              }).catch((err: BusinessError) => {
                console.error('photoPicker.select failed with err: ' + JSON.stringify(err));
              });
            } catch (error) {
              let err: BusinessError = error as BusinessError;
              console.error('photoPicker failed with err: ' + JSON.stringify(err));
            }
          })
        }
      }
    }
    
*   方法二：
    
    1.  创建图库选择器实例，调用select()接口拉起photoPicker界面进行图片选择。图片选择成功后，返回PhotoSelectResult结果集。
    2.  待界面从图库返回后，使用 fileIo.openSync 接口通过 URI 打开文件并获取文件描述符（fd）。注意，接口的权限参数应设置为 fileIo.OpenMode.READ\_ONLY。
    3.  通过 image 使用 image.createImageSource 接口创建图片源实例。
    4.  根据 imageSource 创建 pixelMap。
    
    参考代码如下：
    
    import { photoAccessHelper } from '@kit.MediaLibraryKit';
    import { BusinessError } from '@kit.BasicServicesKit';
    import { image } from '@kit.ImageKit';
    import { fileIo } from '@kit.CoreFileKit';
    
    @Entry
    @Component
    struct WebComponent {
      build() {
        Column() {
          Button('Select Picture').onClick(() => {
            try {
              let uris: Array<string> = \[\];
              let PhotoSelectOptions = new photoAccessHelper.PhotoSelectOptions();
              PhotoSelectOptions.MIMEType = photoAccessHelper.PhotoViewMIMETypes.IMAGE\_TYPE;
              PhotoSelectOptions.maxSelectNumber = 1;
              let photoPicker = new photoAccessHelper.PhotoViewPicker();
              photoPicker.select(PhotoSelectOptions).then((PhotoSelectResult: photoAccessHelper.PhotoSelectResult) => {
                uris = PhotoSelectResult.photoUris;
                let file = fileIo.openSync(uris\[0\], fileIo.OpenMode.READ\_ONLY);
                console.info('file fd: ' + file.fd);
                let buffer = new ArrayBuffer(4096);
                let readLen = fileIo.readSync(file.fd, buffer);
                console.info('readSync data to file succeed and buffer size is:' + readLen);
                const imageSource: image.ImageSource = image.createImageSource(file.fd);
                let decodingOptions: image.DecodingOptions = {
                  editable: true,
                  desiredPixelFormat: 3,
                }
                imageSource.createPixelMap(decodingOptions, (err: BusinessError, pixelMap: image.PixelMap) => {
                  if (err !== undefined) {
                    console.error(\`Failed to create pixelMap.code is ${err.code},message is ${err.message}\`);
                  } else {
                    console.info('Succeeded in creating pixelMap object.');
                  }
                })
              }).catch((err: BusinessError) => {
                console.error(\`Invoke photoPicker.select failed, code is ${err.code}, message is ${err.message}\`);
              })
            } catch (error) {
              let err: BusinessError = error as BusinessError;
              console.error('photoPicker failed with err: ' + JSON.stringify(err));
            }
          })
        }
      }
    }