Android 7.0 安装apk

背景：
Android 7.0后直接把文件的Uri暴露给其它APP会抛出android.os.FileUriExposedException异常，只能通过FileProvider的方式向其它APP暴露文件。

具体步骤
1.在Manifest中声明provider

<manifest>
    ...
    <application>
        ...
        <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/<file_paths_name>" />
        ...
    </application>
</manifest>

2.在res/xml目录下创建<file_paths_name>.xml，替provider指明对外公开的目录。只有在该xml中引入的目录下的文件才能对外分享成功，如果一个文件不在声明的目录中，分享给外部APP的时候回抛出异常java.lang.IllegalArgumentException: Failed to find configured root that contains...

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <files-path name="file" path="files/"/>
    <files-path name="images" path="images/"/>
    <external-path  name="external_file" path="/"/>
</paths>

3.获取文件对外的uri

    private Uri getUriForFile(File file) {
        Uri uri = null;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            uri = FileProvider.getUriForFile(this, getPackageName() + ".provider", file);
        } else {
            uri = Uri.fromFile(file);
        }
        return uri;
    }

4.安装apk

    private void installApk() {
        File dir = Environment.getExternalStorageDirectory();
        File apkFile = new File(dir, "test.apk");
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(getUriForFile(apkFile), "application/vnd.android.package-archive");
        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION); // 这一行代码不要漏掉，否则外部还是无法读取到文件
        startActivity(intent);
    }

参考：
https://developer.android.com/reference/android/support/v4/content/FileProvider.html#Permissions