Android Installing APK.txt

If you want install application programmatically in Android 10, You need to give permission to install app for your application
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Steps 1: Give permission in Manifest
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<uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

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Step 2: Write provider in Android Manifest
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<provider
        android:name="androidx.core.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>

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Step 3: Create file in XML folder named as provider_paths.xml and write
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<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path
        name="files_root"
        path="Android/data/${applicationId}" />
    <external-path
        name="external_files"
        path="." />
</paths>

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Step 4: Give runtime permission for apk installation and storage permissions
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//installtion permission

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                if (!getPackageManager().canRequestPackageInstalls()) {
                    startActivityForResult(new Intent(Settings.ACTION_MANAGE_UNKNOWN_APP_SOURCES).setData(Uri.parse(String.format("package:%s", getPackageName()))), 1234);
                } else {
                }
    }

    //Storage Permission

    if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE,Manifest.permission.READ_EXTERNAL_STORAGE}, 1);
            }

            if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
    }

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Step 5: Call install apk function
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void installAPK(){

    String PATH = Environment.getExternalStorageDirectory() + "/" + "apkname.apk";
    File file = new File(PATH);
    if(file.exists()) {
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(uriFromFile(getApplicationContext(), new File(PATH)), "application/vnd.android.package-archive");
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        try {
            getApplicationContext().startActivity(intent);
        } catch (ActivityNotFoundException e) {
            e.printStackTrace();
            Log.e("TAG", "Error in opening the file!");
        }
    }else{
        Toast.makeText(getApplicationContext(),"installing",Toast.LENGTH_LONG).show();
    }
}
Uri uriFromFile(Context context, File file) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
        return FileProvider.getUriForFile(context, BuildConfig.APPLICATION_ID + ".provider", file);
    } else {
        return Uri.fromFile(file);
    }
}