1. 查看系统是否已经安装某个应用

private boolean appInstalledOrNot(String uri) {
    PackageManager pm = getPackageManager();
    boolean appInstalled;
    try {
        pm.getPackageInfo(uri, 0);
        appInstalled = true;
    }
    catch (PackageManager.NameNotFoundException e) {
        appInstalled = false;
    }
    return appInstalled;
}

 uri是指AndroidManifest.xml文件中的package，是安卓应用的标识符。

2. 判断安装的版本号

private int getAPKVersion(String uri) {
    Integer version = -1;

    PackageManager packageManager=getPackageManager();
    try {
    	//0 means all the flags are turned off
        PackageInfo Info=packageManager.getPackageInfo(uri, 0);

        //like 5
        version = Info.versionCode;

        //like 1.0.5
        versionName = Info.versionName;

    } catch (PackageManager.NameNotFoundException e) {
        Log.e("error", e.getMessage());
    }

    return version;
}

3. 安装

基本思路：apk放到assets目录下，安装时先写到sd，再调用intent安装

private void installScannerPlugin() {
    AssetManager assetManager = getAssets();

    InputStream in;
    OutputStream out;

    try {
        in = assetManager.open("BarcodeScanner.apk");
        out = new FileOutputStream(Environment.getExternalStorageDirectory()
                + File.separator + "BarcodeScanner.apk");

        byte[] buffer = new byte[1024];

        int len;
        while((len = in.read(buffer)) != -1) {
            out.write(buffer, 0, len);
        }

        in.close();

        out.flush();
        out.close();

        Intent intent = new Intent(Intent.ACTION_VIEW);

        intent.setDataAndType(Uri.fromFile(new File(Environment.getExternalStorageDirectory()
                        + File.separator + "BarcodeScanner.apk")),
                "application/vnd.android.package-archive");

        startActivity(intent);

    } catch(Exception e) {
        e.printStackTrace();
    }
}

 需要权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

注意：如果是APP通过自动下载apk安装升级，在安装时务必要加上

installIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

 否则安装完成之后将没有“完成”和“打开”这样的选项提供选择，程序直接退出。