ActivityManager(三)--判断应用程序从后台回到前台

MainActivity如下:

package cc.testbackgroundtofront;

import java.util.List;
import android.app.Activity;
import android.app.ActivityManager;
import android.app.ActivityManager.RunningTaskInfo;
import android.content.ComponentName;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.widget.Toast;
/**
 * Demo描述:
 * 判断应用从后台回到前台
 * 即按下Home键后重新进入到应用
 */
public class MainActivity extends Activity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
	}

	@Override
	protected void onResume() {
		super.onResume();

	}

	@Override
	protected void onRestart() {
		super.onRestart();
		SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
		boolean isCurrentRunningForeground = prefs.getBoolean("isCurrentRunningForeground", false);
		if (!isCurrentRunningForeground) {
			Toast.makeText(MainActivity.this, "从后台回来", Toast.LENGTH_SHORT).show();
		}
	}
	@Override
	protected void onStop() {
		super.onStop();
		try {
			Thread.sleep(1000);
			new Thread(){
				public void run() {
					boolean isCurrentRunningForeground=isRunningForeground();
					SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
					Editor editor=prefs.edit();
					editor.putBoolean("isCurrentRunningForeground", isCurrentRunningForeground);
					editor.commit();
				};
			}.start();
		} catch (Exception e) {

		}
	}

	public boolean isRunningForeground(){
		String packageName=getPackageName(this);
		String topActivityClassName=getTopActivityName(this);
		System.out.println("packageName="+packageName+",topActivityClassName="+topActivityClassName);
		if (packageName!=null&&topActivityClassName!=null&&topActivityClassName.startsWith(packageName)) {
			System.out.println("---> isRunningForeGround");
			return true;
		} else {
			System.out.println("---> isRunningBackGround");
			return false;
		}
	}

	public  String getTopActivityName(Context context){
		String topActivityClassName=null;
		 ActivityManager activityManager =
		(ActivityManager)(context.getSystemService(android.content.Context.ACTIVITY_SERVICE )) ;
		 //android.app.ActivityManager.getRunningTasks(int maxNum)
		 //int maxNum--->The maximum number of entries to return in the list
		 //即最多取得的运行中的任务信息(RunningTaskInfo)数量
	     List<RunningTaskInfo> runningTaskInfos = activityManager.getRunningTasks(1) ;
	     if(runningTaskInfos != null){
	    	 ComponentName f=runningTaskInfos.get(0).topActivity;
	    	 topActivityClassName=f.getClassName();

	     }
	     //按下Home键盘后 topActivityClassName=com.android.launcher2.Launcher
	     return topActivityClassName;
	}

	public String getPackageName(Context context){
		 String packageName = context.getPackageName();
		 return packageName;
	}

}

main.xml如下:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="判断应用是否是由后台回到前台"
        android:layout_centerInParent="true"
     />

</RelativeLayout>