获取当前的activity

ActivityStackManager.java

import android.app.Activity;

import java.lang.ref.WeakReference;
import java.util.Stack;

/**
 * 获取当前的activity
 * 两种思路：    1.弱引用持有当前activity
 *              2.使用栈维护所有的activity，然后获取栈顶的activity
 * 参考：https://www.jianshu.com/p/77f754446009
 */
public class ActivityStackManager {
    private Stack<Activity> activities = new Stack<Activity>();
    private WeakReference<Activity> sCurrentActivityWeakRef;

    public Activity getCurrentActivity() {
        Activity currentActivity = null;
        if (sCurrentActivityWeakRef != null) {
            currentActivity = sCurrentActivityWeakRef.get();
        }
        return currentActivity;
    }

    public void setCurrentActivity(Activity activity) {
        sCurrentActivityWeakRef = new WeakReference<Activity>(activity);
    }

    public Activity getTopActivity(){
        if (activities != null && activities.size() > 0) {
            return activities.peek();
        }
        return null;
    }

    public void setTopActivity(Activity activity){
        if (activities != null && activities.size() > 0) {
            if (activities.search(activity) == -1) {
                activities.push(activity);
                return;
            }

            int location = activities.search(activity);
            if (location != 1) {
                activities.remove(activity);
                activities.push(activity);
            }
        }
    }
}