Intent 安装应用，兼容6.0+

【step1】在res文件夹中创建xml文件夹，创建 provider_paths.xml，内容如下

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <paths>
   <!--     &lt;!&ndash;相当于Context.getFilesDir() + /path/&ndash;&gt;
        <files-path name="name" path="path" />
       &lt;!&ndash; 物理路径相当于Context.getCacheDir() + /path/&ndash;&gt;
        <cache-path name="name" path="path" />
        &lt;!&ndash;物理路径相当于Environment.getExternalStorageDirectory() + /path/&ndash;&gt;
        <external-path name="name" path="path" />
       &lt;!&ndash; 物理路径相当于Context.getExternalFilesDir(String) + /path/&ndash;&gt;
        <external-files-path name="name" path="path" />
       &lt;!&ndash; 物理路径相当于Context.getExternalCacheDir() + /path/&ndash;&gt;
        <external-cache-path name="name" path="path" />-->
        <external-path name="files_root" path="storage/emulated/" />
        <external-path name="external_files" path="."/>
    </paths>
</resources>

【step2】在Mainifest.xml中添加如下内容：

 <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="${applicationId}.provider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/provider_paths"/>
        </provider>

还要配置SD卡读写权限

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

【step3】安装核心代码如下(这里使用了RxPermissions动态权限申请框架)：

rxPermissions.request(Manifest.permission.WRITE_EXTERNAL_STORAGE,
                        Manifest.permission.READ_EXTERNAL_STORAGE)
                        .subscribe(granted -> {
                            if (granted) {
                                install();
                            } else {
                                Toast.makeText(MainActivity.this, "拒绝了相关权限", Toast.LENGTH_SHORT).show();
                            }
                        });

private void install() {
        String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/";
        File file = new File(path, "app.apk");

        Log.e("tag", path);
        Intent intent = new Intent(Intent.ACTION_VIEW);
        // 判断版本大于等于7.0
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            Log.e("tag", "---1111->>" + file.getPath());
            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            // 给目标应用一个临时授权
            intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
            intent.addFlags(Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
            Uri data = FileProvider.getUriForFile(MainActivity.this, BuildConfig.APPLICATION_ID + ".provider", file);
            intent.setDataAndType(data, "application/vnd.android.package-archive");
        } else {
            Log.e("tag", "--2222-->>");
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            //intent.setDataAndType(Uri.parse("file://" + path), "application/vnd.android.package-archive");
            intent.setDataAndType(Uri.fromFile(file), "application/vnd.android.package-archive");
        }
        startActivity(intent);
    }

大功告成！！！