有时候，需要获取当前位于栈顶的activity的实例。这里介绍2种方法，以及各自适用的场景。最后有demo测试数据以供参考
第一种方法：获取栈顶activity的实例 应用场景：项目中，activity都继承于一个BaseActivity，在这个base中，有个广播接收器，收到广播，就弹出一个dialog。现打开多个activity，这个时候，通过三方推送等方法，发出一个广播，base接收到。因为只需要在栈顶的activity弹出，而不是每个activity都弹出，所以，需要获取栈顶activity的实例（即上下文，传给dialog的构造方法），而不能简单的传个this，否则，会导致每个activity都有dialog弹出。
获取方法： 在application中：
public class MyApplication extends Application { PRivate static MyApplication mInstance; private Activity app_activity = null; @Override public void onCreate() { super.onCreate(); mInstance = this; initGlobeActivity(); } private void initGlobeActivity() { registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() { @Override public void onActivityCreated(Activity activity, Bundle savedInstanceState) { app_activity = activity; Log.e("onActivityCreated===", app_activity + ""); } @Override public void onActivityDestroyed(Activity activity) { app_activity = activity; Log.e("onActivityDestroyed===", app_activity + ""); } /** Unused implementation **/ @Override public void onActivityStarted(Activity activity) { app_activity = activity; Log.e("onActivityStarted===", app_activity + ""); } @Override public void onActivityResumed(Activity activity) { app_activity = activity; Log.e("onActivityResumed===", app_activity + ""); } @Override public void onActivityPaused(Activity activity) { app_activity = activity; Log.e("onActivityPaused===", app_activity + ""); } @Override public void onActivityStopped(Activity activity) { app_activity = activity; Log.e("onActivityStopped===", app_activity + ""); } @Override public void onActivitySaveInstanceState(Activity activity, Bundle outState) { } }); } /** * 获取实例 * @return */ public static MyApplication getInstance() { return mInstance; } /** * 公开方法，外部可通过 MyApplication.getInstance().getCurrentActivity() 获取到当前最上层的activity */ public Activity getCurrentActivity() { return app_activity; }}注意：initGlobeActivity()、getInstance()、getCurrentActivity() 这3个方法
使用方法： 在base的展示dialog方法中：
Activity currentActivity = MyApplication.getInstance().getCurrentActivity();Dialog dialog = new Dialog(currentActivity, R.style.PushDialog);————————————————————————————————–
第二种方法：获取栈顶activity的完整包名 应用场景：仅仅为了判断当前activity是不是在栈顶，以便决定要不要弹toast等等。 注意：获取到的仅仅是完整包名，判断当前activity在不在栈顶，需要用到String方法中的contains方法等。这个时候需要注意，以免出错。如：栈顶activity名为AB，里面包含A，就认为A是在栈顶，就出错了。最好这个activity的名字很特殊，和其他的没有重合部分
在工具类中创建方法：
/** * 获得栈中最顶层的Activity * * @param context * @return */ public static String getTopActivity(Context context) { android.app.ActivityManager manager = (android.app.ActivityManager) context.getSystemService(context.ACTIVITY_SERVICE); List<ActivityManager.RunningTaskInfo> runningTaskInfos = manager.getRunningTasks(1); if (runningTaskInfos != null) { return (runningTaskInfos.get(0).topActivity).toString(); } else return null; }使用：
String topActivity_1 = Util.getTopActivity(this);Log.e("topActivity_1", topActivity_1);测试数据： 现有3个activity：MainActivity_1、MainActivity_2、MainActivity_3 第一个中有按钮，点击跳转到第二个，第二个中有按钮，点击跳转到第三个 代码：
package com.chen.demo;import android.app.Activity;import android.os.Bundle;import android.view.Window;/** * 基础Activity */public abstract class BaseActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //不显示title requestWindowFeature(Window.FEATURE_NO_TITLE); initview(); } abstract void initview();}package com.chen.demo;import android.content.Intent;import android.util.Log;import android.view.View;import android.widget.TextView;public class MainActivity_1 extends BaseActivity { TextView tv; @Override void initview() { setContentView(R.layout.activity_main_1); String topActivity_1 = Util.getTopActivity(this); Log.e("topActivity_1", topActivity_1); tv = (TextView) findViewById(R.id.tv); tv.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { MainActivity_1.this.startActivity(new Intent(MainActivity_1.this, MainActivity_2.class)); } }); }}import android.content.Intent;import android.util.Log;import android.view.View;import android.widget.TextView;public class MainActivity_2 extends BaseActivity { TextView tv_2; @Override void initview() { setContentView(R.layout.activity_main_2); String topActivity_2 = Util.getTopActivity(this); Log.e("topActivity_2", topActivity_2); tv_2 = (TextView) findViewById(R.id.tv_2); tv_2.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { MainActivity_2.this.startActivity(new Intent(MainActivity_2.this, MainActivity_3.class)); } }); }}package com.chen.demo;import android.util.Log;public class MainActivity_3 extends BaseActivity { @Override void initview() { setContentView(R.layout.activity_main_3); String topActivity_3 = Util.getTopActivity(this); Log.e("topActivity_3", topActivity_3); }}日志：
程序刚启动02-24 10:56:12.997 13043-13043/com.chen.demo E/onActivityCreated===: com.chen.demo.MainActivity_1@eff3d7802-24 10:56:13.030 13043-13043/com.chen.demo E/topActivity_1: ComponentInfo{com.chen.demo/com.chen.demo.MainActivity_1}02-24 10:56:13.032 13043-13043/com.chen.demo E/onActivityStarted===: com.chen.demo.MainActivity_1@eff3d7802-24 10:56:13.032 13043-13043/com.chen.demo E/onActivityResumed===: com.chen.demo.MainActivity_1@eff3d78点击MainActivity_1中按钮去往MainActivity_202-24 10:56:47.692 13043-13043/com.chen.demo E/onActivityPaused===: com.chen.demo.MainActivity_1@eff3d7802-24 10:56:47.718 13043-13043/com.chen.demo E/onActivityCreated===: com.chen.demo.MainActivity_2@53c82a702-24 10:56:47.722 13043-13043/com.chen.demo E/topActivity_2: ComponentInfo{com.chen.demo/com.chen.demo.MainActivity_2}02-24 10:56:47.724 13043-13043/com.chen.demo E/onActivityStarted===: com.chen.demo.MainActivity_2@53c82a702-24 10:56:47.724 13043-13043/com.chen.demo E/onActivityResumed===: com.chen.demo.MainActivity_2@53c82a702-24 10:56:48.099 13043-13043/com.chen.demo E/onActivityStopped===: com.chen.demo.MainActivity_1@eff3d78点击MainActivity_2中按钮去往MainActivity_302-24 10:57:21.984 13043-13043/com.chen.demo E/onActivityPaused===: com.chen.demo.MainActivity_2@53c82a702-24 10:57:21.999 13043-13043/com.chen.demo E/onActivityCreated===: com.chen.demo.MainActivity_3@f2b18ec02-24 10:57:22.003 13043-13043/com.chen.demo E/topActivity_3: ComponentInfo{com.chen.demo/com.chen.demo.MainActivity_3}02-24 10:57:22.003 13043-13043/com.chen.demo E/onActivityStarted===: com.chen.demo.MainActivity_3@f2b18ec02-24 10:57:22.003 13043-13043/com.chen.demo E/onActivityResumed===: com.chen.demo.MainActivity_3@f2b18ec02-24 10:57:22.382 13043-13043/com.chen.demo E/onActivityStopped===: com.chen.demo.MainActivity_2@53c82a7新闻热点
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