初始化项目

data/src/main/ets/grid/LobBuffer.ets

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+/**
+ * 大字段（LOB）分块缓冲（1.7.7）。
+ *
+ * 大文本/二进制按固定大小分块加载与编辑：
+ * - 只请求可视范围内的块，避免一次性读取整列；
+ * - 记录已加载块，read 拼接时若跨未加载块则抛错（提示先加载）。
+ */
+export class LobBuffer {
+  private readonly totalSize: number;
+  private readonly chunkSize: number;
+  private readonly loaded: Map<number, string> = new Map<number, string>();
+
+  constructor(totalSize: number, chunkSize: number) {
+    if (chunkSize < 1) {
+      throw new Error('chunkSize must be >= 1');
+    }
+    this.totalSize = totalSize < 0 ? 0 : totalSize;
+    this.chunkSize = chunkSize;
+  }
+
+  size(): number {
+    return this.totalSize;
+  }
+
+  chunkCount(): number {
+    return Math.ceil(this.totalSize / this.chunkSize);
+  }
+
+  chunkLength(index: number): number {
+    if (index < 0 || index >= this.chunkCount()) {
+      return 0;
+    }
+    const start: number = index * this.chunkSize;
+    const remaining: number = this.totalSize - start;
+    return remaining < this.chunkSize ? remaining : this.chunkSize;
+  }
+
+  /** 覆盖 [offset, offset+length) 需要的块号。 */
+  chunksFor(offset: number, length: number): number[] {
+    if (this.totalSize === 0 || length <= 0) {
+      return [];
+    }
+    const start: number = offset < 0 ? 0 : offset;
+    const end: number = Math.min(this.totalSize, start + length);
+    if (end <= start) {
+      return [];
+    }
+    const first: number = Math.floor(start / this.chunkSize);
+    const last: number = Math.floor((end - 1) / this.chunkSize);
+    const out: number[] = [];
+    for (let index = first; index <= last; index++) {
+      out.push(index);
+    }
+    return out;
+  }
+
+  setChunk(index: number, data: string): void {
+    if (index < 0 || index >= this.chunkCount()) {
+      return;
+    }
+    this.loaded.set(index, data);
+  }
+
+  isLoaded(index: number): boolean {
+    return this.loaded.has(index);
+  }
+
+  loadedChunks(): number {
+    return this.loaded.size;
+  }
+
+  loadedBytes(): number {
+    let bytes: number = 0;
+    this.loaded.forEach((data: string, index: number) => {
+      bytes += data.length;
+    });
+    return bytes;
+  }
+
+  /** 是否需要加载（覆盖范围内有未加载块）。 */
+  needsLoad(offset: number, length: number): boolean {
+    const chunks: number[] = this.chunksFor(offset, length);
+    for (let i = 0; i < chunks.length; i++) {
+      if (!this.loaded.has(chunks[i])) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /** 读取区间；跨未加载块时抛错。 */
+  read(offset: number, length: number): string {
+    const start: number = offset < 0 ? 0 : offset;
+    const end: number = Math.min(this.totalSize, start + length);
+    if (end <= start) {
+      return '';
+    }
+    const chunks: number[] = this.chunksFor(start, end - start);
+    for (let i = 0; i < chunks.length; i++) {
+      if (!this.loaded.has(chunks[i])) {
+        throw new Error('chunk ' + chunks[i] + ' not loaded');
+      }
+    }
+    let out: string = '';
+    for (let i = 0; i < chunks.length; i++) {
+      out += this.loaded.get(chunks[i]) as string;
+    }
+    const sliceStart: number = start - chunks[0] * this.chunkSize;
+    const sliceEnd: number = sliceStart + (end - start);
+    return out.substring(sliceStart, sliceEnd);
+  }
+
+  /** 全部块已加载。 */
+  isComplete(): boolean {
+    return this.chunkCount() === 0 || this.loaded.size === this.chunkCount();
+  }
+}