前一段时间做项目，频繁使用到上传图片组件，而且只上传一个封面，于是想着自定义一个图片封面上传组件。先来看一下效果：
              
第一张图片是上传之前，第二张图片是上传成功后，第3张图片是鼠标放上去之后的效果！
 
首先整理需求，图片上传我们使用照片墙的方式，只能上传一张图片，图片上传成功后不能继续上传，如果想要更换图片，则需要将图片删除后重新上传。点击图片上面的放大镜可以查看大图。需要限制图片上传的格式，图片的大小。

组件代码：

<template>
  <div class="upload">
    <el-upload
      :class="{'hidden':mFileList.length > 0}"
      list-type="picture-card"
      :on-remove="handleRemove"
      :action="action"
      :before-upload="beforeUploadHandle"
      :on-success="successHandle"
      :on-change="changeHandle"
      :limit="1"
      :accept="accept"
      :on-exceed="handleExceed"
      :file-list="fileList"
      :on-preview="handlePictureCardPreview"
    >
      <i class="el-icon-plus"></i>
    </el-upload>
    <el-dialog :visible.sync="dialogVisible">
      <img width="100%" :src="dialogImageUrl" alt="" />
    </el-dialog>
  </div>
</template>

<script>
export default {
  props: {
    action: {
      type: String,
      default: "",
    },
    accept: {
      type: String,
      default: "",
    },
    fileList:{
      type: Array,
      default: () => [],
    },
  },
  watch: {
    fileList(newValue, oldValue) {
      this.mFileList = newValue
    }
  },
  data() {
    return {
      dialogVisible: false, //图片放大 www.duidaima.com
      fileImg: "", //上传图片
      dialogImageUrl: "", //图片地址
      mFileList:this.fileList,
    };
  },
  methods: {
    handleRemove(file, fileList) {
      this.$emit("upload-remove", file);
    },
    handlePictureCardPreview(file) {
      this.dialogImageUrl = file.url;
      this.dialogVisible = true;
    },
    // 上传之前
    beforeUploadHandle(file) {
      if (file.type !== "image/jpeg" && file.type !== "image/png") {
        this.$message({
          message: "只支持jpg、png格式的图片！",
          type: "warning",
        });
        return false;
      }
      const isLt2M = file.size / 1024 / 1024 < 2;
      if (!isLt2M) {
        this.$message({
          message: "上传文件大小不能超过 2MB!",
          type: "warning",
        });
        return false;
      }
    },
    // 上传成功
    successHandle(response, file, fileList) {
      this.mFileList = fileList;
      if (response && response.code === 200) {
        this.$message.success("图片上传成功！");
        this.$emit("upload-success", response, file);
      } else {
        this.$message.error(response.msg);
      }
    },
    changeHandle(file, fileList) {
      if(file.response && file.response.code == 500) {
         this.$emit("upload-error",file);
      }
    },
    handleExceed(files, fileList) {
        this.$message.warning("只能上传1张图片！");
      },
  },
};
</script>
<style lang="scss">
.upload .hidden .el-upload--picture-card {
  display: none;
}
</style>

调用组件代码：

<template>
  <div class="upload">
    <el-upload
      :class="{'hidden':mFileList.length > 0}"
      list-type="picture-card"
      :on-remove="handleRemove"
      :action="action"
      :before-upload="beforeUploadHandle"
      :on-success="successHandle"
      :on-change="changeHandle"
      :limit="1"
      :accept="accept"
      :on-exceed="handleExceed"
      :file-list="fileList"
      :on-preview="handlePictureCardPreview"
    >
      <i class="el-icon-plus"></i>
    </el-upload>
    <el-dialog :visible.sync="dialogVisible">
      <img width="100%" :src="dialogImageUrl" alt="" />
    </el-dialog>
  </div>
</template>

<script>
export default {
  props: {
    action: {
      type: String,
      default: "",
    },
    accept: {
      type: String,
      default: "",
    },
    fileList:{
      type: Array,
      default: () => [],
    },
  },
  watch: {
    fileList(newValue, oldValue) {
      this.mFileList = newValue
    }
  },
  data() {
    return {
      dialogVisible: false, //图片放大
      fileImg: "", //上传图片
      dialogImageUrl: "", //图片地址
      mFileList:this.fileList,
    };
  },
  methods: {
    handleRemove(file, fileList) {
      this.$emit("upload-remove", file);
    },
    handlePictureCardPreview(file) {
      this.dialogImageUrl = file.url;
      this.dialogVisible = true;
    },
    // 上传之前
    beforeUploadHandle(file) {
      if (file.type !== "image/jpeg" && file.type !== "image/png") {
        this.$message({
          message: "只支持jpg、png格式的图片！",
          type: "warning",
        });
        return false;
      }
      const isLt2M = file.size / 1024 / 1024 < 2;
      if (!isLt2M) {
        this.$message({
          message: "上传文件大小不能超过 2MB!",
          type: "warning",
        });
        return false;
      }
    },
    // 上传成功
    successHandle(response, file, fileList) {
      this.mFileList = fileList;
      if (response && response.code === 200) {
        this.$message.success("图片上传成功！");
        this.$emit("upload-success", response, file);
      } else {
        this.$message.error(response.msg);
      }
    },
    changeHandle(file, fileList) {
      if(file.response && file.response.code == 500) {
         this.$emit("upload-error",file);
      }
    },
    handleExceed(files, fileList) {
        this.$message.warning("只能上传1张图片！");
      },
  },
};
</script>
<style lang="scss">
.upload .hidden .el-upload--picture-card {
  display: none;
}
</style>

点击上传后的图片上的放大镜，显示图片大图: