2种判断（获取）栈顶activity的方法

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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);

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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

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