Intent启动另一个App的三种方法

一、

Intent intent = new Intent();
PackageManager packageManager = getPackageManager();
intent = packageManager.getLaunchIntentForPackage("com.etwod.weidian");
startActivity(intent);

二、

Intent intent = new Intent(Intent.ACTION_MAIN);  
intent.addCategory(Intent.CATEGORY_LAUNCHER);              
ComponentName cn = new ComponentName("com.etwod.weidian", "com.weidian.activity.WelcomeActivity");//包名，全路径类名              
intent.setComponent(cn);  
startActivity(intent);

三、

private void doStartApplicationWithPackageName(String packagename) {  

        // 通过包名获取此APP详细信息，包括Activities、services、versioncode、name等等  
        PackageInfo packageinfo = null;  
        try {  
            packageinfo = getPackageManager().getPackageInfo(packagename, 0);  
        } catch (NameNotFoundException e) {  
            e.printStackTrace();  
        }  
        if (packageinfo == null) {  
            return;  
        }  

        // 创建一个类别为CATEGORY_LAUNCHER的该包名的Intent  
        Intent resolveIntent = new Intent(Intent.ACTION_MAIN, null);  
        resolveIntent.addCategory(Intent.CATEGORY_LAUNCHER);  
        resolveIntent.setPackage(packageinfo.packageName);  

        // 通过getPackageManager()的queryIntentActivities方法遍历  
        List<ResolveInfo> resolveinfoList = getPackageManager()  
                .queryIntentActivities(resolveIntent, 0);  

        ResolveInfo resolveinfo = resolveinfoList.iterator().next();  
        if (resolveinfo != null) {  
            // packagename = 参数packname  
            String packageName = resolveinfo.activityInfo.packageName;  
            // 这个就是我们要找的该APP的LAUNCHER的Activity[组织形式：packagename.mainActivityname]  
            String className = resolveinfo.activityInfo.name;  
            // LAUNCHER Intent  
            Intent intent = new Intent(Intent.ACTION_MAIN);  
            intent.addCategory(Intent.CATEGORY_LAUNCHER);  

            // 设置ComponentName参数1:packagename参数2:MainActivity路径  
            ComponentName cn = new ComponentName(packageName, className);  

            intent.setComponent(cn);  
            startActivity(intent);  
        }  
    }