一般Activity 切换到后台

@Override
    public void onBackPressed() {
        ResolveInfo launcherResolve=queryCurrentLauncher();
        Intent intent=new Intent();
        intent.addCategory(Intent.ACTION_MAIN);
        ComponentName componentName=new ComponentName(launcherResolve.activityInfo.packageName,launcherResolve.activityInfo.name);
        intent.setComponent(componentName);
        startActivitySafely(intent);
    }
    private void startActivitySafely(Intent intent){
        try{
            startActivity(intent);
            Toast.makeText(this, "切换到后台成功", Toast.LENGTH_SHORT).show();
        }catch (Exception e){
            Toast.makeText(this, "切换到后台失败", Toast.LENGTH_SHORT).show();
            e.printStackTrace();
        }
    }

    private ResolveInfo queryCurrentLauncher() {
        Intent launcherIntent = new Intent(Intent.ACTION_MAIN);
        launcherIntent.addCategory(Intent.CATEGORY_HOME);
        launcherIntent.addCategory(Intent.CATEGORY_DEFAULT);
        List<ResolveInfo> launcherInfoList = getPackageManager().queryIntentActivities(launcherIntent, PackageManager.MATCH_DEFAULT_ONLY);

        ResolveInfo launcherResolveInfo = null;
        ActivityManager activityManager = (ActivityManager) getSystemService(Service.ACTIVITY_SERVICE);
        List<ActivityManager.RunningTaskInfo> tasks = activityManager.getRunningTasks(30);
        Iterator<ActivityManager.RunningTaskInfo> itInfo = tasks.iterator();
        while (itInfo.hasNext()) {
            ActivityManager.RunningTaskInfo info = itInfo.next();
            for (ResolveInfo resolveInfo : launcherInfoList) {
                String name1 = info.topActivity.getClassName();
                String namme2 = resolveInfo.activityInfo.name;
                if (name1.equals(namme2)) {
                    //获取当前使用的桌面
                    launcherResolveInfo = resolveInfo;
                    return launcherResolveInfo;
                }
            }
        }
        return launcherResolveInfo;
    }