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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 volatile 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();
}
}
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