CloseGuard 類別

定義

[Android.Runtime.Register("android/util/CloseGuard", ApiSince=30, DoNotGenerateAcw=true)]
public sealed class CloseGuard : Java.Lang.Object

[<Android.Runtime.Register("android/util/CloseGuard", ApiSince=30, DoNotGenerateAcw=true)>]
type CloseGuard = class
    inherit Object

繼承

Object

JavaObject

Object

CloseGuard

屬性

RegisterAttribute

備註

CloseGuard 是一種用來標記資源隱式終結子清理的機制，這些資源本應由明確的 Close 方法（在 Effective Java 中的「明確終止方法」）來清理。

簡單的範例：

{@code
              class Foo {

                  private final CloseGuard guard = new CloseGuard();

                  ...

                  public Foo() {
                      ...;
                      guard.open("cleanup");
                  }

                  public void cleanup() {
                     guard.close();
                     ...;
                     if (Build.VERSION.SDK_INT >= 28) {
                         Reference.reachabilityFence(this);
                     }
                     // For full correctness in the absence of a close() call, other methods may also need
                     // reachabilityFence() calls.
                  }

                  protected void finalize() throws Throwable {
                      try {
                          // Note that guard could be null if the constructor threw.
                          if (guard != null) {
                              guard.warnIfOpen();
                          }
                          cleanup();
                      } finally {
                          super.finalize();
                      }
                  }
              }
            }

在物件建構後明確分配資源時，CloseGuard 保護可以延後。 例如：

{@code
              class Bar {

                  private final CloseGuard guard = new CloseGuard();

                  ...

                  public Bar() {
                      ...;
                  }

                  public void connect() {
                     ...;
                     guard.open("cleanup");
                  }

                  public void cleanup() {
                     guard.close();
                     ...;
                     if (Build.VERSION.SDK_INT >= 28) {
                         Reference.reachabilityFence(this);
                     }
                     // For full correctness in the absence of a close() call, other methods may also need
                     // reachabilityFence() calls.
                  }

                  protected void finalize() throws Throwable {
                      try {
                          // Note that guard could be null if the constructor threw.
                          if (guard != null) {
                              guard.warnIfOpen();
                          }
                          cleanup();
                      } finally {
                          super.finalize();
                      }
                  }
              }
            }

在建構子中使用時，呼叫 open 應發生在建構子的結尾，因為導致建構子突然終止的例外將意味著使用者無法明確參考該物件來清理。 在方法中使用時，呼叫 open 應在資源取得後立即發生。

Java 文件 android.util.CloseGuard。

本頁部分內容為基於 Open Source Project 所創建與分享的作品，並依授權條款所描述的使用進行修改。