Use a cancellable handler when loading, storing and refreshing caches

This closes #685.

1 files changed, 112 insertions, 0 deletions

diff --git a/main/src/cgeo/geocaching/utils/CancellableHandler.java b/main/src/cgeo/geocaching/utils/CancellableHandler.java
new file mode 100644
index 0000000..0b490d8
--- /dev/null
+++ b/main/src/cgeo/geocaching/utils/CancellableHandler.java
@@ -0,0 +1,112 @@
+package cgeo.geocaching.utils;
+
+import android.os.Handler;
+import android.os.Message;
+
+/**
+ * Handler with a cancel policy. Once cancelled, the handler will not handle
+ * any more cancel or regular message.
+ */
+public abstract class CancellableHandler extends Handler {
+
+    private boolean cancelled = false;
+
+    private static class CancelHolder {
+        final Object payload;
+
+        CancelHolder(final Object payload) {
+            this.payload = payload;
+        }
+    }
+
+    @Override
+    final public void handleMessage(final Message message) {
+        if (cancelled) {
+            return;
+        }
+
+        if (message.obj instanceof CancelHolder) {
+            cancelled = true;
+            handleCancel(((CancelHolder) message.obj).payload);
+        } else {
+            handleRegularMessage(message);
+        }
+    }
+
+    /**
+     * Handle a non-cancel message.<br>
+     * Subclasses must implement this to handle messages.
+     *
+     * @param message
+     *            the message to handle
+     */
+    abstract protected void handleRegularMessage(final Message message);
+
+    /**
+     * Handle a cancel message.
+     *
+     * @param extra
+     *            the additional payload given by the canceller
+     */
+    protected void handleCancel(final Object extra) {
+    }
+
+    /**
+     * Get a cancel message that can later be sent to this handler to cancel it.
+     *
+     * @return a cancel message
+     */
+    public Message cancelMessage() {
+        return cancelMessage(null);
+    }
+
+    /**
+     * Get a cancel message with an additional parameter that can later be sent to
+     * this handler to cancel it.
+     *
+     * @param extra
+     *            the extra parameter to give to the cancel handler
+     * @return a cancel message
+     */
+    public Message cancelMessage(final Object extra) {
+        return this.obtainMessage(0, new CancelHolder(extra));
+    }
+
+    /**
+     * Cancel the current handler. This can be called from any thread.
+     */
+    public void cancel() {
+        cancel(null);
+    }
+
+    /**
+     * Cancel the current handler. This can be called from any thread.
+     *
+     * @param extra
+     *            the extra parameter to give to the cancel handler
+     */
+    public void cancel(final Object extra) {
+        cancelMessage(extra).sendToTarget();
+    }
+
+    /**
+     * Check if the current handler has been cancelled.
+     *
+     * @return true if the handler has been cancelled
+     */
+    public boolean isCancelled() {
+        return cancelled;
+    }
+
+    /**
+     * Check if a handler has been cancelled.
+     *
+     * @param handler
+     *            a handler, or null
+     * @return true if the handler is not null and has been cancelled
+     */
+    public static boolean isCancelled(final CancellableHandler handler) {
+        return handler != null && handler.isCancelled();
+    }
+
+}